AI Trajectory

null

{
  "EnableConfigs": [
    "KVM",
    "KVM_INTEL"
  ],
  "FocusSymbols": [
    "nested_vmx_enter_non_root_mode",
    "nested_vmx_check_restored_vmcs12",
    "vmx_handle_exit"
  ],
  "KMSANReasoning": "The patch fixes an issue in KVM's nested virtualization where a failure in `nested_get_vmcs12_pages` could leave the vCPU in guest mode with stale host physical addresses (HPAs) mapped in vmcs02. If userspace resumed the vCPU, hardware could access these stale HPAs, leading to memory corruption or use-after-free-like behavior. The fix re-arms the `KVM_REQ_GET_NESTED_STATE_PAGES` request to ensure KVM retries the mapping.\n\nThis issue is related to stale pointers and invalid memory accesses, not uninitialized memory. The patch does not introduce any new data structures, allocations, or data copied to userspace that could expose uninitialized memory. Standard KASAN or other memory corruption detectors are more appropriate for catching use-after-free or invalid access bugs. Therefore, a dedicated KMSAN fuzzing session is not necessary.",
  "NeedsKMSAN": false,
  "Reasoning": "The patch fixes a bug in KVM's nested VMX implementation where a failure to map VMCS12 pages would leave the vCPU in guest mode with stale host physical addresses. This is a functional change in core virtualization logic that is reachable from userspace via KVM ioctls (e.g., KVM_SET_NESTED_STATE or VM-Enter). Fuzzing is highly recommended.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 68936ee3d7a0fb9f82a7de6dbf2ebd29dcd9c164\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Thu Aug 13 05:42:42 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c\nindex ddf6df7bee93b..9e9bd6c541baa 100644\n--- a/arch/x86/kvm/vmx/nested.c\n+++ b/arch/x86/kvm/vmx/nested.c\n@@ -3453,7 +3453,7 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)\n \t\t * state which can lead to a load of wrong PDPTRs.\n \t\t */\n \t\tif (CC(!load_pdptrs(vcpu, vcpu-\u003earch.cr3)))\n-\t\t\treturn false;\n+\t\t\tgoto fail;\n \t}\n \n \n@@ -3469,7 +3469,7 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)\n \t\t\tvcpu-\u003erun-\u003einternal.suberror =\n \t\t\t\tKVM_INTERNAL_ERROR_EMULATION;\n \t\t\tvcpu-\u003erun-\u003einternal.ndata = 0;\n-\t\t\treturn false;\n+\t\t\tgoto fail;\n \t\t}\n \t}\n \n@@ -3525,6 +3525,20 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)\n \t\texec_controls_clearbit(vmx, CPU_BASED_USE_MSR_BITMAPS);\n \n \treturn true;\n+\n+fail:\n+\t/*\n+\t * Re-arm the request so that KVM retries the mapping instead of running\n+\t * L2 with a stale vmcs02.  Bailing here leaves the vCPU in guest mode\n+\t * with vmcs02 loaded and its APIC-access, virtual-APIC and posted\n+\t * interrupt descriptor addresses still pointing at the host pages that\n+\t * were mapped for the *previous* nested VM-Enter, which have since been\n+\t * unmapped and unpinned by nested_put_vmcs12_pages().  KVM returns to\n+\t * userspace without leaving guest mode, so if userspace resumes the\n+\t * vCPU, VM-Enter succeeds and hardware accesses those stale HPAs.\n+\t */\n+\tkvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);\n+\treturn false;\n }\n \n static bool vmx_get_nested_state_pages(struct kvm_vcpu *vcpu)\n"
}

best-expensive

null

{
  "EnableConfigs": [
    "KVM",
    "KVM_INTEL"
  ],
  "FocusSymbols": [
    "nested_vmx_enter_non_root_mode",
    "nested_vmx_check_restored_vmcs12",
    "vmx_handle_exit"
  ],
  "Reasoning": "The patch fixes a bug in KVM's nested VMX implementation where a failure to map VMCS12 pages would leave the vCPU in guest mode with stale host physical addresses. This is a functional change in core virtualization logic that is reachable from userspace via KVM ioctls (e.g., KVM_SET_NESTED_STATE or VM-Enter). Fuzzing is highly recommended.",
  "WorthFuzzing": true
}

You are an expert Linux kernel maintainer.
Your job is to review a provided patch series and determine
if it makes functional changes to the kernel that should be fuzzed.

IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on your internal knowledge of the kernel. You must actively
use your code access tools to examine the actual source code and confirm any assumptions.

Return WorthFuzzing=false if the patch only contains:
- Modifications to Documentation/, Kconfig files, or code comments.
- Purely decorative changes, such as logging (e.g., pr_err, printk) or tracepoints.
- Changes to numeric constants or macros that do not functionally alter execution flow.
- Code paths that are impossible to reach in virtualized environments like GCE or QEMU,
  even when utilizing software-emulated hardware (e.g., usb gadget, mac80211_hwsim).
- Code in vendor-specific PCIe switch, SmartNIC, or GPU drivers (e.g., mlxsw, pds_core, qed,
  ionic, amdgpu) that require physical PCIe hardware cards not emulated in standard QEMU.
- Driver .remove, .shutdown, or pci_unregister_driver teardown callbacks (e.g., igb_remove)
  that are executed only during PCI hot-unplug or sysfs driver unbind operations.

If it modifies reachable core kernel logic, drivers, or architectures, use your code search
tools to verify the code can be executed, then return WorthFuzzing=true.

When returning WorthFuzzing=true, you MUST ALSO:
1. Extract any specific kernel functions that should be heavily fuzzed into FocusSymbols.
   Avoid listing generic hot-path functions to prevent skewed test distributions.
   Prefer non-static, non-inlined API entrypoint functions over internal static helper functions
   (which are inlined by the compiler and do not have distinct symbol addresses).
2. Identify any specific CONFIG_ options required to properly test this new/modified feature.
   Go and look into the Kconfig files and check for ifdefs around the code, do not make assumptions.
   Also check "depends on" lines in Kconfig to include any non-standard parent subsystem configs
   needed for Kbuild to compile the code statically into vmlinux. List them in the EnableConfigs
   output array, and DO NOT add a 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4").
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

For your convenience, here is the diff of the changes:
commit 68936ee3d7a0fb9f82a7de6dbf2ebd29dcd9c164
Author: syz-cluster <triage@syzkaller.com>
Date:   Thu Aug 13 05:42:42 2026 +0000

    syz-cluster: applied patch under review

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index ddf6df7bee93b..9e9bd6c541baa 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3453,7 +3453,7 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
 		 * state which can lead to a load of wrong PDPTRs.
 		 */
 		if (CC(!load_pdptrs(vcpu, vcpu->arch.cr3)))
-			return false;
+			goto fail;
 	}
 
 
@@ -3469,7 +3469,7 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
 			vcpu->run->internal.suberror =
 				KVM_INTERNAL_ERROR_EMULATION;
 			vcpu->run->internal.ndata = 0;
-			return false;
+			goto fail;
 		}
 	}
 
@@ -3525,6 +3525,20 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
 		exec_controls_clearbit(vmx, CPU_BASED_USE_MSR_BITMAPS);
 
 	return true;
+
+fail:
+	/*
+	 * Re-arm the request so that KVM retries the mapping instead of running
+	 * L2 with a stale vmcs02.  Bailing here leaves the vCPU in guest mode
+	 * with vmcs02 loaded and its APIC-access, virtual-APIC and posted
+	 * interrupt descriptor addresses still pointing at the host pages that
+	 * were mapped for the *previous* nested VM-Enter, which have since been
+	 * unmapped and unpinned by nested_put_vmcs12_pages().  KVM returns to
+	 * userspace without leaving guest mode, so if userspace resumes the
+	 * vCPU, VM-Enter succeeds and hardware accesses those stale HPAs.
+	 */
+	kvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
+	return false;
 }
 
 static bool vmx_get_nested_state_pages(struct kvm_vcpu *vcpu)

gemini-3.1-pro-preview

null

null

							input: 2406
							output: 37
							thoughts: 189
						

**Analyzing a Potential KVM VMX Vulnerability**

Okay, so I've got this patch here that's poking around in `arch/x86/kvm/vmx/nested.c`.  It seems to be addressing a bug in `nested_get_vmcs12_pages`. The code now handles a failure by jumping to `fail`, re-arming the `KVM_REQ_GET_NESTED_STATE_PAGES` request, and then returning `false`. The change has to do with how the function handles errors when retrieving nested VMCS12 pages. The fact that it re-arms the request after failure and returns `false` is the key thing I'm focused on.

My initial thought is to dive into `nested_get_vmcs12_pages` and its associated function `vmx_get_nested_state_pages`. The context is KVM's x86 nested VMX code, so definitely worth a fuzzing campaign to see if any of these changes introduces new issues. The re-arming of the request after the failure seems like the most interesting part. I'll need to figure out what happens in the event of this "fail" condition.

I need to confirm the relevant configuration options. `CONFIG_KVM` and `CONFIG_KVM_INTEL` should do the trick. Now I'll head over to `arch/x86/kvm/Kconfig` to verify the configuration details.

{
  "Expression": "config KVM_INTEL",
  "PathPrefix": "arch/x86/kvm/Kconfig"
}

{
  "Output": "arch/x86/kvm/Kconfig=83=config KVM_SW_PROTECTED_VM\n--\narch/x86/kvm/Kconfig-95-\narch/x86/kvm/Kconfig:96:config KVM_INTEL\narch/x86/kvm/Kconfig-97-\ttristate \"KVM for Intel (and compatible) processors support\"\n--\narch/x86/kvm/Kconfig-106-\narch/x86/kvm/Kconfig:107:config KVM_INTEL_PROVE_VE\narch/x86/kvm/Kconfig-108-        bool \"Check that guests do not receive #VE exceptions\"\n--\narch/x86/kvm/Kconfig=122=config X86_SGX_KVM\n--\narch/x86/kvm/Kconfig-133-\narch/x86/kvm/Kconfig:134:config KVM_INTEL_TDX\narch/x86/kvm/Kconfig-135-\tbool \"Intel Trust Domain Extensions (TDX) support\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 3238
							output: 37
							thoughts: 51
						

Okay, here's my take on those thoughts, framed as my own:

**KVM Module Dependency Review**

Alright, so I'm diving into this KVM stuff again. I know `KVM_INTEL` is the key configuration option I'm after, that's a given. But wait, `KVM` itself is also essential, right? I can't just enable `KVM_INTEL` in isolation. I need to make sure I have the fundamental `KVM` support in place first.

Time to drill down. Let's get into the nitty-gritty and see what the dependencies are for `KVM_INTEL`. I'll head over to `arch/x86/kvm/Kconfig` in the kernel source. That's where I'll find the definitive answer regarding its dependencies and what other configuration options need to be set or enabled. No point in assuming; better to verify the relationships directly within the Kconfig files.

{
  "Expression": "config KVM_INTEL",
  "PathPrefix": "arch/x86/kvm/Kconfig"
}

{
  "Output": "arch/x86/kvm/Kconfig=83=config KVM_SW_PROTECTED_VM\n--\narch/x86/kvm/Kconfig-95-\narch/x86/kvm/Kconfig:96:config KVM_INTEL\narch/x86/kvm/Kconfig-97-\ttristate \"KVM for Intel (and compatible) processors support\"\n--\narch/x86/kvm/Kconfig-106-\narch/x86/kvm/Kconfig:107:config KVM_INTEL_PROVE_VE\narch/x86/kvm/Kconfig-108-        bool \"Check that guests do not receive #VE exceptions\"\n--\narch/x86/kvm/Kconfig=122=config X86_SGX_KVM\n--\narch/x86/kvm/Kconfig-133-\narch/x86/kvm/Kconfig:134:config KVM_INTEL_TDX\narch/x86/kvm/Kconfig-135-\tbool \"Intel Trust Domain Extensions (TDX) support\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 3828
							output: 38
							thoughts: 23
						

Here's a summary of my thought process, as requested:

**Diving into KVM Configuration**

Okay, time to get my hands dirty. I need to understand something specific about KVM's x86 configuration. To get a handle on it, I'm going to jump straight into the source code – specifically, the Kconfig file for the x86 architecture. I'm thinking the relevant section will be around line 96 in `arch/x86/kvm/Kconfig`. That usually gives me a good starting point for exploring features and dependencies in this area. Time to fire up the editor and see what's what! I’m hoping to find the relevant configuration options.

{
  "File": "arch/x86/kvm/Kconfig",
  "FirstLine": 90,
  "LineCount": 20
}

{
  "Contents": "  90:\t\t  protected VMs are purely a development and testing vehicle for\n  91:\t\t  KVM_CREATE_GUEST_MEMFD.  Attempting to run a \"real\" VM workload as a\n  92:\t\t  software-protected VM will fail miserably.\n  93:\t\n  94:\t\t  If unsure, say \"N\".\n  95:\t\n  96:\tconfig KVM_INTEL\n  97:\t\ttristate \"KVM for Intel (and compatible) processors support\"\n  98:\t\tdepends on KVM \u0026\u0026 IA32_FEAT_CTL\n  99:\t\tselect X86_FRED if X86_64\n 100:\t\thelp\n 101:\t\t  Provides support for KVM on processors equipped with Intel's VT\n 102:\t\t  extensions, a.k.a. Virtual Machine Extensions (VMX).\n 103:\t\n 104:\t\t  To compile this as a module, choose M here: the module\n 105:\t\t  will be called kvm-intel.\n 106:\t\n 107:\tconfig KVM_INTEL_PROVE_VE\n 108:\t        bool \"Check that guests do not receive #VE exceptions\"\n 109:\t        depends on KVM_INTEL \u0026\u0026 EXPERT\n"
}

gemini-3.1-pro-preview

null

null

							input: 4371
							output: 45
							thoughts: 117
						

**Analyzing the KVM Patch**

Okay, so I see this patch involves `KVM` and specifically `KVM_INTEL`, which is important context. My initial instinct is to zero in on the core changes, and the function that's being modified is `nested_get_vmcs12_pages`. Right, so this patch affects that specific function.

Let me confirm, is `nested_get_vmcs12_pages` static? Ah, yes, it is. Wait a second, the diff confirms that it’s `static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)`.

Now, I need to understand the impact of this change. To do that, I need to trace the call paths to figure out how `nested_get_vmcs12_pages` is actually being used. I need to find all of its callers now.

{
  "Expression": "nested_get_vmcs12_pages",
  "PathPrefix": "arch/x86/kvm/vmx/nested.c"
}

{
  "Output": "arch/x86/kvm/vmx/nested.c=912=static int nested_vmx_check_apicv_controls(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/vmx/nested.c-938-\t * the descriptor address has been already checked\narch/x86/kvm/vmx/nested.c:939:\t * in nested_get_vmcs12_pages.\narch/x86/kvm/vmx/nested.c-940-\t *\n--\narch/x86/kvm/vmx/nested.c=2431=static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct loaded_vmcs *vmcs01,\n--\narch/x86/kvm/vmx/nested.c-2481-\t/*\narch/x86/kvm/vmx/nested.c:2482:\t * This bit will be computed in nested_get_vmcs12_pages, because\narch/x86/kvm/vmx/nested.c-2483-\t * we do not have access to L1's MSR bitmap yet.  For now, keep\n--\narch/x86/kvm/vmx/nested.c=3413=static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/nested.c-3441-\narch/x86/kvm/vmx/nested.c:3442:static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)\narch/x86/kvm/vmx/nested.c-3443-{\n--\narch/x86/kvm/vmx/nested.c=3544=static bool vmx_get_nested_state_pages(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/nested.c-3564-\narch/x86/kvm/vmx/nested.c:3565:\tif (is_guest_mode(vcpu) \u0026\u0026 !nested_get_vmcs12_pages(vcpu))\narch/x86/kvm/vmx/nested.c-3566-\t\treturn false;\n--\narch/x86/kvm/vmx/nested.c=3643=enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/vmx/nested.c-3695-\tif (from_vmentry) {\narch/x86/kvm/vmx/nested.c:3696:\t\tif (unlikely(!nested_get_vmcs12_pages(vcpu))) {\narch/x86/kvm/vmx/nested.c-3697-\t\t\tvmx_switch_vmcs(vcpu, \u0026vmx-\u003evmcs01);\n--\narch/x86/kvm/vmx/nested.c-3730-\t\t * need to perform gpa to hpa translation). Request a call\narch/x86/kvm/vmx/nested.c:3731:\t\t * to nested_get_vmcs12_pages before the next VM-entry.  The MSRs\narch/x86/kvm/vmx/nested.c-3732-\t\t * have already been set at vmentry time and should not be reset.\n--\narch/x86/kvm/vmx/nested.c=6912=static int vmx_set_nested_state(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/vmx/nested.c-7014-\t\t * restored yet. EVMCS will be mapped from\narch/x86/kvm/vmx/nested.c:7015:\t\t * nested_get_vmcs12_pages().\narch/x86/kvm/vmx/nested.c-7016-\t\t */\n"
}

gemini-3.1-pro-preview

null

null

							input: 5769
							output: 47
							thoughts: 76
						

Here's my thinking process:

**Diving into the VMX Code**

Okay, so I see `vmx_get_nested_state_pages` and `nested_vmx_enter_non_root_mode` are calling each other, interesting. I need to understand how these functions interact. First, I'll take a quick look at `vmx_get_nested_state_pages` to see if it's static, and yes, it is. That's good to know for scoping and potential inlining. Now, let's turn our attention to `nested_vmx_enter_non_root_mode` itself. I need to trace its logic and understand its role in this nested virtualization scenario.

{
  "Expression": "nested_vmx_enter_non_root_mode",
  "PathPrefix": "arch/x86/kvm/vmx/nested.c"
}

{
  "Output": "arch/x86/kvm/vmx/nested.c=3630=static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/vmx/nested.c-3642- */\narch/x86/kvm/vmx/nested.c:3643:enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,\narch/x86/kvm/vmx/nested.c-3644-\t\t\t\t\t\t\tbool from_vmentry)\n--\narch/x86/kvm/vmx/nested.c=3798=static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)\n--\narch/x86/kvm/vmx/nested.c-3877-\tvmx-\u003enested.has_preemption_timer_deadline = false;\narch/x86/kvm/vmx/nested.c:3878:\tstatus = nested_vmx_enter_non_root_mode(vcpu, true);\narch/x86/kvm/vmx/nested.c-3879-\tif (unlikely(status != NVMX_VMENTRY_SUCCESS))\n--\narch/x86/kvm/vmx/nested.c-3885-\t/*\narch/x86/kvm/vmx/nested.c:3886:\t * Must happen outside of nested_vmx_enter_non_root_mode() as it will\narch/x86/kvm/vmx/nested.c-3887-\t * also be used as part of restoring nVMX state for\n--\narch/x86/kvm/vmx/nested.c=6912=static int vmx_set_nested_state(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/vmx/nested.c-7079-\tvmx-\u003enested.force_msr_bitmap_recalc = true;\narch/x86/kvm/vmx/nested.c:7080:\tret = nested_vmx_enter_non_root_mode(vcpu, false);\narch/x86/kvm/vmx/nested.c-7081-\tif (ret)\n"
}

gemini-3.1-pro-preview

null

null

							input: 6649
							output: 41
							thoughts: 55
						

Here's my summary, as if I were thinking these thoughts:

**Analyzing Potential Non-Static Functions in Nested VMX**

Okay, so `nested_vmx_enter_non_root_mode`... I thought it might be static, but the grep results say otherwise. That's unusual. It's time to dig deeper. If that one isn't static, maybe there's a pattern, or a logical reason for this. Let's shift our focus and investigate `nested_vmx_run` and `vmx_set_nested_state`. They're likely related, and the scope of these functions will probably provide valuable context. I need to understand why `nested_vmx_enter_non_root_mode` is *not* static, and these related functions should hopefully shed some light. This could indicate a subtle design choice, and I need to be prepared for the implications that aren't immediately obvious, potentially in how the VM exits the VMX context.

{
  "Expression": "nested_vmx_run",
  "PathPrefix": "arch/x86/kvm/vmx/nested.c"
}

{
  "Output": "arch/x86/kvm/vmx/nested.c=3643=enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/vmx/nested.c-3794-/*\narch/x86/kvm/vmx/nested.c:3795: * nested_vmx_run() handles a nested entry, i.e., a VMLAUNCH or VMRESUME on L1\narch/x86/kvm/vmx/nested.c-3796- * for running an L2 nested guest.\narch/x86/kvm/vmx/nested.c-3797- */\narch/x86/kvm/vmx/nested.c:3798:static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)\narch/x86/kvm/vmx/nested.c-3799-{\n--\narch/x86/kvm/vmx/nested.c=5648=static int handle_vmlaunch(struct kvm_vcpu *vcpu)\narch/x86/kvm/vmx/nested.c-5649-{\narch/x86/kvm/vmx/nested.c:5650:\treturn nested_vmx_run(vcpu, true);\narch/x86/kvm/vmx/nested.c-5651-}\n--\narch/x86/kvm/vmx/nested.c=5654=static int handle_vmresume(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/nested.c-5656-\narch/x86/kvm/vmx/nested.c:5657:\treturn nested_vmx_run(vcpu, false);\narch/x86/kvm/vmx/nested.c-5658-}\n"
}

gemini-3.1-pro-preview

null

null

							input: 7463
							output: 43
							thoughts: 32
						

Here's my take on the thought process, as if it were my own:

**Investigating VMX State Transitions**

Okay, so I'm looking at `handle_vmlaunch` and `handle_vmresume`, and the first thing that jumps out is that they're defined as `static`. Right, that's not unusual for handlers like this, but it's a good reminder of their scope within the module. Now, I need to understand how these routines interact with the nested virtualization state. The key here is likely going to be how the hardware manages the state across those calls. Time to check `vmx_set_nested_state`. That function is probably where the magic happens.

{
  "Expression": "vmx_set_nested_state",
  "PathPrefix": "arch/x86/kvm/vmx/nested.c"
}

{
  "Output": "arch/x86/kvm/vmx/nested.c=6890=int nested_vmx_check_restored_vmcs12(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/nested.c-6911-\narch/x86/kvm/vmx/nested.c:6912:static int vmx_set_nested_state(struct kvm_vcpu *vcpu,\narch/x86/kvm/vmx/nested.c-6913-\t\t\t\tstruct kvm_nested_state __user *user_kvm_nested_state,\n--\narch/x86/kvm/vmx/nested.c=7497=struct kvm_x86_nested_ops vmx_nested_ops = {\n--\narch/x86/kvm/vmx/nested.c-7504-\t.get_state = vmx_get_nested_state,\narch/x86/kvm/vmx/nested.c:7505:\t.set_state = vmx_set_nested_state,\narch/x86/kvm/vmx/nested.c-7506-\t.get_nested_state_pages = vmx_get_nested_state_pages,\n"
}

gemini-3.1-pro-preview

null

null

							input: 8018
							output: 47
							thoughts: 92
						

**Analyzing the Nested VMX Operations**

Okay, so I'm diving into how `vmx_nested_ops` functions, specifically its dependence on `vmx_get_nested_state_pages` and `vmx_set_nested_state`. My goal here is to understand the entry points, the external interfaces for this module. I'll need to identify non-static functions within `arch/x86/kvm/vmx/nested.c` that act as these entry points.

Let me see... Ah, there's `nested_vmx_enter_non_root_mode`. That looks promising. Now, I need to quickly confirm that it isn't declared as a static function, since that would make it inaccessible from outside this file. Hopefully, it's exposed for use. This will give me a clear entry point to trace the execution flow.

{
  "Expression": "nested_vmx_enter_non_root_mode",
  "PathPrefix": "arch/x86/kvm/vmx/nested.c"
}

{
  "Output": "arch/x86/kvm/vmx/nested.c=3630=static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/vmx/nested.c-3642- */\narch/x86/kvm/vmx/nested.c:3643:enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,\narch/x86/kvm/vmx/nested.c-3644-\t\t\t\t\t\t\tbool from_vmentry)\n--\narch/x86/kvm/vmx/nested.c=3798=static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)\n--\narch/x86/kvm/vmx/nested.c-3877-\tvmx-\u003enested.has_preemption_timer_deadline = false;\narch/x86/kvm/vmx/nested.c:3878:\tstatus = nested_vmx_enter_non_root_mode(vcpu, true);\narch/x86/kvm/vmx/nested.c-3879-\tif (unlikely(status != NVMX_VMENTRY_SUCCESS))\n--\narch/x86/kvm/vmx/nested.c-3885-\t/*\narch/x86/kvm/vmx/nested.c:3886:\t * Must happen outside of nested_vmx_enter_non_root_mode() as it will\narch/x86/kvm/vmx/nested.c-3887-\t * also be used as part of restoring nVMX state for\n--\narch/x86/kvm/vmx/nested.c=6912=static int vmx_set_nested_state(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/vmx/nested.c-7079-\tvmx-\u003enested.force_msr_bitmap_recalc = true;\narch/x86/kvm/vmx/nested.c:7080:\tret = nested_vmx_enter_non_root_mode(vcpu, false);\narch/x86/kvm/vmx/nested.c-7081-\tif (ret)\n"
}

gemini-3.1-pro-preview

null

null

							input: 8945
							output: 44
							thoughts: 48
						

**My Initial Assessment**

Okay, so I'm looking at this `nested_vmx_enter_non_root_mode` function and the first thing that jumps out is that it's *not* a static function. That's a key observation. Now, I have to consider the implications of that... If it's not static, the bigger question becomes: is this function exposed for use outside the `nested.c` file itself? Is it declared in a header or used by another module?

{
  "Expression": "nested_vmx_enter_non_root_mode",
  "PathPrefix": "arch/x86/kvm/vmx/"
}

{
  "Output": "arch/x86/kvm/vmx/nested.c=3630=static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/vmx/nested.c-3642- */\narch/x86/kvm/vmx/nested.c:3643:enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,\narch/x86/kvm/vmx/nested.c-3644-\t\t\t\t\t\t\tbool from_vmentry)\n--\narch/x86/kvm/vmx/nested.c=3798=static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)\n--\narch/x86/kvm/vmx/nested.c-3877-\tvmx-\u003enested.has_preemption_timer_deadline = false;\narch/x86/kvm/vmx/nested.c:3878:\tstatus = nested_vmx_enter_non_root_mode(vcpu, true);\narch/x86/kvm/vmx/nested.c-3879-\tif (unlikely(status != NVMX_VMENTRY_SUCCESS))\n--\narch/x86/kvm/vmx/nested.c-3885-\t/*\narch/x86/kvm/vmx/nested.c:3886:\t * Must happen outside of nested_vmx_enter_non_root_mode() as it will\narch/x86/kvm/vmx/nested.c-3887-\t * also be used as part of restoring nVMX state for\n--\narch/x86/kvm/vmx/nested.c=6912=static int vmx_set_nested_state(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/vmx/nested.c-7079-\tvmx-\u003enested.force_msr_bitmap_recalc = true;\narch/x86/kvm/vmx/nested.c:7080:\tret = nested_vmx_enter_non_root_mode(vcpu, false);\narch/x86/kvm/vmx/nested.c-7081-\tif (ret)\n--\narch/x86/kvm/vmx/nested.h-10-/*\narch/x86/kvm/vmx/nested.h:11: * Status returned by nested_vmx_enter_non_root_mode():\narch/x86/kvm/vmx/nested.h-12- */\n--\narch/x86/kvm/vmx/nested.h=26=void nested_vmx_free_vcpu(struct kvm_vcpu *vcpu);\narch/x86/kvm/vmx/nested.h:27:enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,\narch/x86/kvm/vmx/nested.h-28-\t\t\t\t\t\t     bool from_vmentry);\n--\narch/x86/kvm/vmx/vmx.c=8420=int vmx_leave_smm(struct kvm_vcpu *vcpu, const union kvm_smram *smram)\n--\narch/x86/kvm/vmx/vmx.c-8434-\narch/x86/kvm/vmx/vmx.c:8435:\t\tret = nested_vmx_enter_non_root_mode(vcpu, false);\narch/x86/kvm/vmx/vmx.c-8436-\t\tif (ret != NVMX_VMENTRY_SUCCESS)\n"
}

gemini-3.1-pro-preview

null

null

							input: 10113
							output: 38
							thoughts: 90
						

Here's my thought process, as I analyze this code:

**Deep Dive into VMX Nesting**

Okay, so I see a crucial function, `vmx_leave_smm`, and it's calling something in `vmx.c`. My spidey-sense tells me this is related to nested VMX operation. Let's dig deeper into the symbol `nested_vmx_enter_non_root_mode`. I'm going to focus my initial analysis on that function.

Now, hold on. I also see `vmx_set_nested_state`. It's static, which is a bit of a red flag in this kind of situation, but it's assigned to `vmx_nested_ops.set_state`. That `vmx_nested_ops` structure is probably where the real action is happening, so I need to check it out. I'll need to understand how it's used to manage the nested VMX environment. I'm going to make sure to check its declaration, and how the `set_state` is used.

{
  "Expression": "vmx_nested_ops",
  "PathPrefix": "arch/x86/kvm/vmx/"
}

{
  "Output": "arch/x86/kvm/vmx/main.c=880=struct kvm_x86_ops vt_x86_ops __initdata = {\n--\narch/x86/kvm/vmx/main.c-997-\narch/x86/kvm/vmx/main.c:998:\t.nested_ops = \u0026vmx_nested_ops,\narch/x86/kvm/vmx/main.c-999-\n--\narch/x86/kvm/vmx/nested.c=7476=static gpa_t vmx_translate_nested_gpa(struct kvm_vcpu *vcpu, gpa_t gpa,\n--\narch/x86/kvm/vmx/nested.c-7496-\narch/x86/kvm/vmx/nested.c:7497:struct kvm_x86_nested_ops vmx_nested_ops = {\narch/x86/kvm/vmx/nested.c-7498-\t.leave_nested = vmx_leave_nested,\n--\narch/x86/kvm/vmx/nested.h=312=static inline bool nested_cpu_has_no_hw_errcode_cc(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/nested.h-320-\narch/x86/kvm/vmx/nested.h:321:extern struct kvm_x86_nested_ops vmx_nested_ops;\narch/x86/kvm/vmx/nested.h-322-\n"
}

gemini-3.1-pro-preview

null

null

							input: 10897
							output: 42
							thoughts: 438
						

**Analyzing Nested VMX Entry Points**

Okay, so I'm diving into this nested VMX code. My initial thought is to figure out the key entry points for fuzzing. I see that `vmx_nested_ops` is used in `main.c` to initialize `vt_x86_ops.nested_ops`. That's a good starting point. I need to understand what's in the symbol table and what's not.

Let's see, `vmx_set_nested_state` is static, which means it might be inlined. I need to confirm whether it's exported and whether syzkaller can reach it. I'll check `nested_vmx_run`, which is also static; it is unlikely to be in the symbol table. `handle_vmlaunch` is also static, so I can probably ignore that, too. The question now is, are there any non-static functions that call `nested_get_vmcs12_pages`? Aha! `nested_vmx_enter_non_root_mode` is *non-static* and it calls that function. That's a strong candidate.

Let's quickly check other functions that might be relevant. `nested_vmx_check_apicv_controls` is static, `prepare_vmcs02_early` is static, `nested_get_evmcs_page` is static, and `vmx_get_nested_state_pages` is static. They're all probably internal helpers.

Now, about `vmx_set_nested_state`. It's static, but it's assigned to a function pointer! That means it won't be inlined. But it *could* still be a hidden symbol, so syzkaller might be able to reach it. That's good to keep in mind, even though it's static. But, based on the prompt, it sounds like I should focus on the non-static functions. `nested_vmx_enter_non_root_mode` is definitely a better focus since it is non-static and not inlined.

I need to expand my search for more non-static functions related to nested VMX. I need to keep searching for any other possible entry points that I might have missed.

{
  "Expression": "^int nested_vmx_",
  "PathPrefix": "arch/x86/kvm/vmx/nested.c"
}

{
  "Output": "arch/x86/kvm/vmx/nested.c=6881=void vmx_leave_nested(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/nested.c-6889-\narch/x86/kvm/vmx/nested.c:6890:int nested_vmx_check_restored_vmcs12(struct kvm_vcpu *vcpu)\narch/x86/kvm/vmx/nested.c-6891-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 12018
							output: 46
							thoughts: 17
						

Here's my attempt at summarizing the thought process, tailored for an expert audience and written in the first person:

**Kernel Investigation: VMX Context & Potential Nesting**

Okay, so I need to quickly identify potential areas of concern within the kernel's VMX handling. My initial instinct is to zero in on any code paths related to nested virtualization, or anything that resembles that type of architecture. The immediate search strategy involves looking for function names or code blocks that might contain `^void nested_vmx_`, or something equally descriptive. I'm deliberately using a wildcard (`^`) at the beginning to grab anything that *precedes* the phrase - in effect looking for potential wrappers or supporting functions that call the function of interest. The goal is to rapidly locate code segments involved with VMX management, and in particular, see if there are any indications of a "nested" execution model. This rapid check should give me a quick signal if I need to dig deeper in that area.

{
  "Expression": "^[a-z_]+ nested_vmx_",
  "PathPrefix": "arch/x86/kvm/vmx/nested.c"
}

{
  "Output": "arch/x86/kvm/vmx/nested.c=336=static void free_nested(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/nested.c-384- */\narch/x86/kvm/vmx/nested.c:385:void nested_vmx_free_vcpu(struct kvm_vcpu *vcpu)\narch/x86/kvm/vmx/nested.c-386-{\n--\narch/x86/kvm/vmx/nested.c=662=static inline\t\t\t\t\t\t\t\t\t\\\narch/x86/kvm/vmx/nested.c:663:void nested_vmx_set_msr_##rw##_intercept(struct vcpu_vmx *vmx,\t\t\t\\\narch/x86/kvm/vmx/nested.c-664-\t\t\t\t\t unsigned long *msr_bitmap_l1,\t\t\\\n--\narch/x86/kvm/vmx/nested.c=6197=static int handle_vmfunc(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/nested.c-6251- */\narch/x86/kvm/vmx/nested.c:6252:bool nested_vmx_check_io_bitmaps(struct kvm_vcpu *vcpu, unsigned int port,\narch/x86/kvm/vmx/nested.c-6253-\t\t\t\t int size)\n--\narch/x86/kvm/vmx/nested.c=6566=static bool nested_vmx_l1_wants_exit(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/vmx/nested.c-6705- */\narch/x86/kvm/vmx/nested.c:6706:bool nested_vmx_reflect_vmexit(struct kvm_vcpu *vcpu)\narch/x86/kvm/vmx/nested.c-6707-{\n--\narch/x86/kvm/vmx/nested.c=6881=void vmx_leave_nested(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/nested.c-6889-\narch/x86/kvm/vmx/nested.c:6890:int nested_vmx_check_restored_vmcs12(struct kvm_vcpu *vcpu)\narch/x86/kvm/vmx/nested.c-6891-{\n--\narch/x86/kvm/vmx/nested.c=6912=static int vmx_set_nested_state(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/vmx/nested.c-7093-\narch/x86/kvm/vmx/nested.c:7094:void nested_vmx_set_vmcs_shadowing_bitmap(void)\narch/x86/kvm/vmx/nested.c-7095-{\n--\narch/x86/kvm/vmx/nested.c=7352=static void nested_vmx_setup_cr_fixed(struct nested_vmx_msrs *msrs)\n--\narch/x86/kvm/vmx/nested.c-7381- */\narch/x86/kvm/vmx/nested.c:7382:void nested_vmx_setup_ctls_msrs(struct vmcs_config *vmcs_conf, u32 ept_caps)\narch/x86/kvm/vmx/nested.c-7383-{\n--\narch/x86/kvm/vmx/nested.c-7418-\narch/x86/kvm/vmx/nested.c:7419:void nested_vmx_hardware_unsetup(void)\narch/x86/kvm/vmx/nested.c-7420-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 13312
							output: 32
							thoughts: 74
						

Here's my summary, as I see it:

**Digging into KVM Nested Virtualization**

Okay, so `nested_vmx_enter_non_root_mode` is looking solid, that seems to be functioning as expected. But now I'm thinking about the bigger picture. What about `vmx_set_nested_state`? It's marked as static, which is interesting, but it's *the* entry point for that `KVM_SET_NESTED_STATE` ioctl. It feels like I need to understand that piece better in relation to what I'm looking at. I'll need to double check how this integrates. Let me go take a look at `kvm_x86_nested_ops`, it should have the information I need on how these pieces are integrated.

{
  "Expression": "set_state",
  "PathPrefix": "arch/x86/kvm/"
}

{
  "Output": "arch/x86/kvm/lapic.c=3293=int kvm_apic_get_state(struct kvm_vcpu *vcpu, struct kvm_lapic_state *s)\n--\narch/x86/kvm/lapic.c-3305-\narch/x86/kvm/lapic.c:3306:int kvm_apic_set_state(struct kvm_vcpu *vcpu, struct kvm_lapic_state *s)\narch/x86/kvm/lapic.c-3307-{\n--\narch/x86/kvm/lapic.h=136=int kvm_apic_get_state(struct kvm_vcpu *vcpu, struct kvm_lapic_state *s);\narch/x86/kvm/lapic.h:137:int kvm_apic_set_state(struct kvm_vcpu *vcpu, struct kvm_lapic_state *s);\narch/x86/kvm/lapic.h-138-int kvm_lapic_find_highest_irr(struct kvm_vcpu *vcpu);\n--\narch/x86/kvm/svm/nested.c=2165=struct kvm_x86_nested_ops svm_nested_ops = {\n--\narch/x86/kvm/svm/nested.c-2172-\t.get_state = svm_get_nested_state,\narch/x86/kvm/svm/nested.c:2173:\t.set_state = svm_set_nested_state,\narch/x86/kvm/svm/nested.c-2174-\t.hv_inject_synthetic_vmexit_post_tlb_flush = svm_hv_inject_synthetic_vmexit_post_tlb_flush,\n--\narch/x86/kvm/vmx/nested.c=7497=struct kvm_x86_nested_ops vmx_nested_ops = {\n--\narch/x86/kvm/vmx/nested.c-7504-\t.get_state = vmx_get_nested_state,\narch/x86/kvm/vmx/nested.c:7505:\t.set_state = vmx_set_nested_state,\narch/x86/kvm/vmx/nested.c-7506-\t.get_nested_state_pages = vmx_get_nested_state_pages,\n--\narch/x86/kvm/x86.c=5310=static int kvm_vcpu_ioctl_set_lapic(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/x86.c-5317-\narch/x86/kvm/x86.c:5318:\tr = kvm_apic_set_state(vcpu, s);\narch/x86/kvm/x86.c-5319-\tif (r)\n--\narch/x86/kvm/x86.c=6189=long kvm_arch_vcpu_ioctl(struct file *filp,\n--\narch/x86/kvm/x86.c-6561-\t\tr = -EINVAL;\narch/x86/kvm/x86.c:6562:\t\tif (!kvm_x86_ops.nested_ops-\u003eset_state)\narch/x86/kvm/x86.c-6563-\t\t\tbreak;\n--\narch/x86/kvm/x86.c-6584-\t\tidx = srcu_read_lock(\u0026vcpu-\u003ekvm-\u003esrcu);\narch/x86/kvm/x86.c:6585:\t\tr = kvm_x86_ops.nested_ops-\u003eset_state(vcpu, user_kvm_nested_state, \u0026kvm_state);\narch/x86/kvm/x86.c-6586-\t\tsrcu_read_unlock(\u0026vcpu-\u003ekvm-\u003esrcu, idx);\n"
}

gemini-3.1-pro-preview

null

null

							input: 14643
							output: 38
							thoughts: 169
						

**My Line of Inquiry into VM Exit Handling**

Okay, so I'm tracing this `kvm_arch_vcpu_ioctl` call, and it ultimately lands in `kvm_x86_ops.nested_ops->set_state`. Given my understanding of the KVM architecture, that immediately raises a flag. I know `vmx_set_nested_state` is a static function, which means I can use `kvm_arch_vcpu_ioctl` as a pretty good focus point, although it is a hot-path generic function.

Now, where does `vmx_set_nested_state` lead? Right, `nested_vmx_enter_non_root_mode` is called from both `vmx_set_nested_state` and `nested_vmx_run`. Interesting, is `nested_vmx_run` also static? Yep, it is. And how about `handle_vmlaunch`? Also static, as expected.

My line of thinking now is to try and identify *non-static* functions that handle VM exits, and if `vmx_handle_exit` is non-static, it should be promising. And indeed, `vmx_handle_exit` is not static.

{
  "Expression": "vmx_handle_exit",
  "PathPrefix": "arch/x86/kvm/vmx/"
}

{
  "Output": "arch/x86/kvm/vmx/main.c=159=static int vt_handle_exit(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/vmx/main.c-164-\narch/x86/kvm/vmx/main.c:165:\treturn vmx_handle_exit(vcpu, fastpath);\narch/x86/kvm/vmx/main.c-166-}\n--\narch/x86/kvm/vmx/main.c=880=struct kvm_x86_ops vt_x86_ops __initdata = {\n--\narch/x86/kvm/vmx/main.c-993-\t.check_intercept = vmx_check_intercept,\narch/x86/kvm/vmx/main.c:994:\t.handle_exit_irqoff = vmx_handle_exit_irqoff,\narch/x86/kvm/vmx/main.c-995-\n--\narch/x86/kvm/vmx/vmx.c=5409=static int handle_exception_nmi(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/vmx.c-5474-\t * MMIO, it is better to report an internal error.\narch/x86/kvm/vmx/vmx.c:5475:\t * See the comments in vmx_handle_exit.\narch/x86/kvm/vmx/vmx.c-5476-\t */\n--\narch/x86/kvm/vmx/vmx.c=6258=static int handle_bus_lock_vmexit(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/vmx.c-6262-\t * VM-Exits. Unconditionally set the flag here and leave the handling to\narch/x86/kvm/vmx/vmx.c:6263:\t * vmx_handle_exit().\narch/x86/kvm/vmx/vmx.c-6264-\t */\n--\narch/x86/kvm/vmx/vmx.c=6491=void dump_vmcs(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/vmx.c-6695- */\narch/x86/kvm/vmx/vmx.c:6696:static int __vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)\narch/x86/kvm/vmx/vmx.c-6697-{\n--\narch/x86/kvm/vmx/vmx.c-6854-\narch/x86/kvm/vmx/vmx.c:6855:int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)\narch/x86/kvm/vmx/vmx.c-6856-{\narch/x86/kvm/vmx/vmx.c:6857:\tint ret = __vmx_handle_exit(vcpu, exit_fastpath);\narch/x86/kvm/vmx/vmx.c-6858-\n--\narch/x86/kvm/vmx/vmx.c=7168=static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/vmx/vmx.c-7183-\narch/x86/kvm/vmx/vmx.c:7184:void vmx_handle_exit_irqoff(struct kvm_vcpu *vcpu)\narch/x86/kvm/vmx/vmx.c-7185-{\n--\narch/x86/kvm/vmx/x86_ops.h=29=void vmx_vcpu_put(struct kvm_vcpu *vcpu);\narch/x86/kvm/vmx/x86_ops.h:30:int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath);\narch/x86/kvm/vmx/x86_ops.h:31:void vmx_handle_exit_irqoff(struct kvm_vcpu *vcpu);\narch/x86/kvm/vmx/x86_ops.h-32-int vmx_skip_emulated_instruction(struct kvm_vcpu *vcpu);\n"
}

gemini-3.1-pro-preview

null

null

							input: 16318
							output: 36
							thoughts: 335
						

**Analyzing Non-Static Functions and a Potential Bug**

Okay, so I'm looking at this code and immediately I see a pattern: `vmx_handle_exit`, `nested_vmx_enter_non_root_mode`, `nested_vmx_check_restored_vmcs12`, `nested_vmx_reflect_vmexit`, `nested_vmx_check_io_bitmaps`, `nested_vmx_free_vcpu`, `nested_vmx_set_vmcs_shadowing_bitmap`, `nested_vmx_setup_ctls_msrs`, and `nested_vmx_hardware_unsetup` – they are all declared as non-static. This likely means they are intended for external use, probably part of an API or exposed for some other module to leverage.

My focus is drawn to this `nested_get_vmcs12_pages` function because I understand that it's the suspected culprit. And it's called by `vmx_get_nested_state_pages` and `nested_vmx_enter_non_root_mode`. I remember the overall architecture and recall the flow from a page fault. It seems `vmx_get_nested_state_pages` leads to `vmx_get_nested_state_pages` through the following chain: `kvm_mmu_do_page_fault` -> `kvm_mmu_page_fault` -> `kvm_mmu_do_page_fault` -> `kvm_mmu_get_page` and then… oh, right, it's assigned to `vmx_nested_ops.get_nested_state_pages`. Excellent, now I understand the path.

I need to see where else `get_nested_state_pages` is actually called to get a better sense of how widespread this problem might be. The issue could be very localized or impact other areas of the system that rely on this functionality. Let's see...

{
  "Expression": "get_nested_state_pages",
  "PathPrefix": "arch/x86/kvm/"
}

{
  "Output": "arch/x86/kvm/svm/nested.c=1950=static int svm_set_nested_state(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/svm/nested.c-2111-\narch/x86/kvm/svm/nested.c:2112:static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)\narch/x86/kvm/svm/nested.c-2113-{\n--\narch/x86/kvm/svm/nested.c=2165=struct kvm_x86_nested_ops svm_nested_ops = {\n--\narch/x86/kvm/svm/nested.c-2170-\t.triple_fault = nested_svm_triple_fault,\narch/x86/kvm/svm/nested.c:2171:\t.get_nested_state_pages = svm_get_nested_state_pages,\narch/x86/kvm/svm/nested.c-2172-\t.get_state = svm_get_nested_state,\n--\narch/x86/kvm/vmx/nested.c=3442=static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/nested.c-3543-\narch/x86/kvm/vmx/nested.c:3544:static bool vmx_get_nested_state_pages(struct kvm_vcpu *vcpu)\narch/x86/kvm/vmx/nested.c-3545-{\n--\narch/x86/kvm/vmx/nested.c=7497=struct kvm_x86_nested_ops vmx_nested_ops = {\n--\narch/x86/kvm/vmx/nested.c-7505-\t.set_state = vmx_set_nested_state,\narch/x86/kvm/vmx/nested.c:7506:\t.get_nested_state_pages = vmx_get_nested_state_pages,\narch/x86/kvm/vmx/nested.c-7507-\t.write_log_dirty = nested_vmx_write_pml_buffer,\n--\narch/x86/kvm/x86.c=11112=static int vcpu_enter_guest(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/x86.c-11134-\t\tif (kvm_check_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu)) {\narch/x86/kvm/x86.c:11135:\t\t\tif (unlikely(!kvm_x86_ops.nested_ops-\u003eget_nested_state_pages(vcpu))) {\narch/x86/kvm/x86.c-11136-\t\t\t\tr = 0;\n"
}

gemini-3.1-pro-preview

null

null

							input: 17898
							output: 34
							thoughts: 488
						

**My Assessment of the KVM Nested Virtualization Fix**

Okay, so `get_nested_state_pages` gets called within `vcpu_enter_guest` when we have a `KVM_REQ_GET_NESTED_STATE_PAGES` request. The patch is interesting because it explicitly re-arms that request within `nested_get_vmcs12_pages` in case of failure. Essentially, it's making sure KVM retries the mapping rather than running L2 with a potentially incorrect `vmcs02`. The key here is that without this, we'd bail out, leaving the vCPU in guest mode with an outdated `vmcs02`, and its addresses pointing to *host* pages that are no longer valid because `nested_put_vmcs12_pages()` has unmapped and unpinned them. KVM would return to userspace, and if that userspace thing resumes the vCPU, VM-Enter would succeed, but we'd have hardware accessing those stale HPAs – a definite recipe for disaster.

This is a clear, functional fix that I think is ripe for fuzzing. I need to focus on the key symbols, specifically `nested_vmx_enter_non_root_mode` and `vmx_handle_exit`. These seem like the critical entry and exit points in this nested virtualization context.

Let's see, are there any other functions that are potentially relevant that aren't static?
Okay, I'll also add these functions to the fuzzing focus list.
`nested_vmx_check_restored_vmcs12` and `nested_vmx_reflect_vmexit`

So I'm going to include in the fuzzing:
- `nested_vmx_enter_non_root_mode`
- `vmx_handle_exit`

Now, before I get carried away, let me just quickly verify the relevant Kconfig options to make sure I'm targeting the right builds. I know it's KVM and KVM_INTEL, but I should double check that there isn't anything else. Checking `arch/x86/kvm/Kconfig` now...

{
  "Expression": "config KVM",
  "PathPrefix": "arch/x86/kvm/Kconfig"
}

{
  "Output": "arch/x86/kvm/Kconfig=18=if VIRTUALIZATION\narch/x86/kvm/Kconfig-19-\narch/x86/kvm/Kconfig:20:config KVM_X86\narch/x86/kvm/Kconfig-21-\tdef_tristate KVM if (KVM_INTEL != n || KVM_AMD != n)\n--\narch/x86/kvm/Kconfig-51-\narch/x86/kvm/Kconfig:52:config KVM\narch/x86/kvm/Kconfig-53-\ttristate \"Kernel-based Virtual Machine (KVM) support\"\n--\narch/x86/kvm/Kconfig-68-\narch/x86/kvm/Kconfig:69:config KVM_WERROR\narch/x86/kvm/Kconfig-70-\tbool \"Compile KVM with -Werror\"\n--\narch/x86/kvm/Kconfig-82-\narch/x86/kvm/Kconfig:83:config KVM_SW_PROTECTED_VM\narch/x86/kvm/Kconfig-84-\tbool \"Enable support for KVM software-protected VMs\"\n--\narch/x86/kvm/Kconfig-95-\narch/x86/kvm/Kconfig:96:config KVM_INTEL\narch/x86/kvm/Kconfig-97-\ttristate \"KVM for Intel (and compatible) processors support\"\n--\narch/x86/kvm/Kconfig-106-\narch/x86/kvm/Kconfig:107:config KVM_INTEL_PROVE_VE\narch/x86/kvm/Kconfig-108-        bool \"Check that guests do not receive #VE exceptions\"\n--\narch/x86/kvm/Kconfig=122=config X86_SGX_KVM\n--\narch/x86/kvm/Kconfig-133-\narch/x86/kvm/Kconfig:134:config KVM_INTEL_TDX\narch/x86/kvm/Kconfig-135-\tbool \"Intel Trust Domain Extensions (TDX) support\"\n--\narch/x86/kvm/Kconfig-145-\narch/x86/kvm/Kconfig:146:config KVM_AMD\narch/x86/kvm/Kconfig-147-\ttristate \"KVM for AMD processors support\"\n--\narch/x86/kvm/Kconfig-155-\narch/x86/kvm/Kconfig:156:config KVM_AMD_SEV\narch/x86/kvm/Kconfig-157-\tbool \"AMD Secure Encrypted Virtualization (SEV) support\"\n--\narch/x86/kvm/Kconfig-171-\narch/x86/kvm/Kconfig:172:config KVM_IOAPIC\narch/x86/kvm/Kconfig-173-\tbool \"I/O APIC, PIC, and PIT emulation\"\n--\narch/x86/kvm/Kconfig-181-\narch/x86/kvm/Kconfig:182:config KVM_SMM\narch/x86/kvm/Kconfig-183-\tbool \"System Management Mode emulation\"\n--\narch/x86/kvm/Kconfig-192-\narch/x86/kvm/Kconfig:193:config KVM_HYPERV\narch/x86/kvm/Kconfig-194-\tbool \"Support for Microsoft Hyper-V emulation\"\n--\narch/x86/kvm/Kconfig-206-\narch/x86/kvm/Kconfig:207:config KVM_XEN\narch/x86/kvm/Kconfig-208-\tbool \"Support for Xen hypercall interface\"\n--\narch/x86/kvm/Kconfig-215-\narch/x86/kvm/Kconfig:216:config KVM_PROVE_MMU\narch/x86/kvm/Kconfig-217-\tbool \"Prove KVM MMU correctness\"\n--\narch/x86/kvm/Kconfig-228-\narch/x86/kvm/Kconfig:229:config KVM_EXTERNAL_WRITE_TRACKING\narch/x86/kvm/Kconfig-230-\tbool\narch/x86/kvm/Kconfig-231-\narch/x86/kvm/Kconfig:232:config KVM_MAX_NR_VCPUS\narch/x86/kvm/Kconfig-233-\tint \"Maximum number of vCPUs per KVM guest\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 20105
							output: 46
							thoughts: 193
						

**My KVM Fuzzing Strategy**

Alright, let's get down to business. My focus is KVM fuzzing, and I know that `KVM` and `KVM_INTEL` are the key configurations. Therefore, I will set `EnableConfigs` to `["KVM", "KVM_INTEL"]`. That's the baseline.

Now, I need to identify the most promising entry points for fuzzing within the `arch/x86/kvm/vmx/nested.c` file. I'm looking for functions that aren't static and likely to be interesting from a fuzzing perspective. Okay, I see `nested_vmx_enter_non_root_mode`, `nested_vmx_reflect_vmexit`, and `nested_vmx_check_restored_vmcs12`. After review, I've decided `nested_vmx_enter_non_root_mode` and `nested_vmx_check_restored_vmcs12` have the most fuzzing potential. I will also include `vmx_handle_exit` in my testing strategy.

Let's quickly verify the details of `nested_vmx_check_restored_vmcs12` to ensure it's a good candidate.

{
  "Expression": "nested_vmx_check_restored_vmcs12",
  "PathPrefix": "arch/x86/kvm/vmx/"
}

{
  "Output": "arch/x86/kvm/vmx/nested.c=6881=void vmx_leave_nested(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/nested.c-6889-\narch/x86/kvm/vmx/nested.c:6890:int nested_vmx_check_restored_vmcs12(struct kvm_vcpu *vcpu)\narch/x86/kvm/vmx/nested.c-6891-{\n--\narch/x86/kvm/vmx/nested.c=6912=static int vmx_set_nested_state(struct kvm_vcpu *vcpu,\n--\narch/x86/kvm/vmx/nested.c-7073-\narch/x86/kvm/vmx/nested.c:7074:\tret = nested_vmx_check_restored_vmcs12(vcpu);\narch/x86/kvm/vmx/nested.c-7075-\tif (ret \u003c 0)\n--\narch/x86/kvm/vmx/nested.h=24=void nested_vmx_set_vmcs_shadowing_bitmap(void);\narch/x86/kvm/vmx/nested.h:25:int nested_vmx_check_restored_vmcs12(struct kvm_vcpu *vcpu);\narch/x86/kvm/vmx/nested.h-26-void nested_vmx_free_vcpu(struct kvm_vcpu *vcpu);\n--\narch/x86/kvm/vmx/vmx.c=8420=int vmx_leave_smm(struct kvm_vcpu *vcpu, const union kvm_smram *smram)\n--\narch/x86/kvm/vmx/vmx.c-8431-\t\t/* Triple fault if the state is invalid.  */\narch/x86/kvm/vmx/vmx.c:8432:\t\tif (nested_vmx_check_restored_vmcs12(vcpu) \u003c 0)\narch/x86/kvm/vmx/vmx.c-8433-\t\t\treturn 1;\n"
}

gemini-3.1-pro-preview

null

null

							input: 21206
							output: 168
							thoughts: 107
						

**My Analysis of VMX Module Symbol Usage**

Okay, so I've traced the usage of `nested_vmx_check_restored_vmcs12`, and confirmed that it's indeed called within `vmx_leave_smm` and `vmx_set_nested_state`. Excellent. This confirms my understanding of how those functions interact.

Given this, I need to keep a laser focus on these specific symbols for further analysis:

*   `nested_vmx_enter_non_root_mode`
*   `nested_vmx_check_restored_vmcs12`
*   `vmx_handle_exit`

That seems to be a solid list of key functions to scrutinize. I'm satisfied with this analysis. Let's get these results set and move on.

{
  "EnableConfigs": [
    "KVM",
    "KVM_INTEL"
  ],
  "FocusSymbols": [
    "nested_vmx_enter_non_root_mode",
    "nested_vmx_check_restored_vmcs12",
    "vmx_handle_exit"
  ],
  "Reasoning": "The patch fixes a bug in KVM's nested VMX implementation where a failure to map VMCS12 pages would leave the vCPU in guest mode with stale host physical addresses. This is a functional change in core virtualization logic that is reachable from userspace via KVM ioctls (e.g., KVM_SET_NESTED_STATE or VM-Enter). Fuzzing is highly recommended.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "KVM",
    "KVM_INTEL"
  ],
  "FocusSymbols": [
    "nested_vmx_enter_non_root_mode",
    "nested_vmx_check_restored_vmcs12",
    "vmx_handle_exit"
  ],
  "Reasoning": "The patch fixes a bug in KVM's nested VMX implementation where a failure to map VMCS12 pages would leave the vCPU in guest mode with stale host physical addresses. This is a functional change in core virtualization logic that is reachable from userspace via KVM ioctls (e.g., KVM_SET_NESTED_STATE or VM-Enter). Fuzzing is highly recommended.",
  "WorthFuzzing": true
}

{
  "WorthFuzzing": true
}

null

best-expensive

null

{
  "KMSANReasoning": "The patch fixes an issue in KVM's nested virtualization where a failure in `nested_get_vmcs12_pages` could leave the vCPU in guest mode with stale host physical addresses (HPAs) mapped in vmcs02. If userspace resumed the vCPU, hardware could access these stale HPAs, leading to memory corruption or use-after-free-like behavior. The fix re-arms the `KVM_REQ_GET_NESTED_STATE_PAGES` request to ensure KVM retries the mapping.\n\nThis issue is related to stale pointers and invalid memory accesses, not uninitialized memory. The patch does not introduce any new data structures, allocations, or data copied to userspace that could expose uninitialized memory. Standard KASAN or other memory corruption detectors are more appropriate for catching use-after-free or invalid access bugs. Therefore, a dedicated KMSAN fuzzing session is not necessary.",
  "NeedsKMSAN": false
}

You are an expert Linux kernel security engineer specializing in kernel memory
error detectors (KASAN and KMSAN). Your job is to review the provided patch series and
determine if the code changes justify spawning a dedicated KMSAN (KernelMemorySanitizer)
fuzzing session in addition to standard KASAN fuzzing.

CRITICAL DISTINCTION BETWEEN KASAN AND KMSAN:
- Standard KASAN kernel builds (upstream-apparmor-kasan.config) already enable
  a comprehensive suite of debugging tools and sanitizers, including KASAN
  (out-of-bounds accesses, use-after-free, double free, invalid free), LOCKDEP
  (locking bugs and deadlocks), UB-sanitizers, and memory corruption checks.
- KMSAN (KernelMemorySanitizer) detects reads of UNINITIALIZED memory (stack, heap,
  or page allocations) and kernel-to-user memory info-leaks.

Rule: THERE IS NO SENSE IN RUNNING A KMSAN SESSION IF A BUG CAN BE CAUGHT BY KASAN,
LOCKDEP, OR OTHER STANDARD BUG DETECTORS.
A dedicated KMSAN fuzzing session incurs significant resource costs. You must ONLY
set NeedsKMSAN=true if the code changes introduce or expose UNINITIALIZED MEMORY risks
that are detected ONLY by KMSAN.

Look holistically at the patch series and surrounding code. Even if no direct
uninitialized field accesses or new buffer allocations are added in the diff itself,
a patch may alter control flow, bounds checking, or data length calculations in ways
that change how the rest of the code operates on existing buffers (e.g. allowing
uninitialized stack/heap memory to be read, copied to user space, or used in control
flow). Do not hesitate to use your code access tools to inspect the surrounding code,
called functions, and callers.

Set NeedsKMSAN=true ONLY IF the patch introduces or modifies:
1. Kernel structures sent to user space (via copy_to_user, put_user, netlink skb
   attributes, ioctl output arguments, socket options, or BPF buffers) where fields
   or structure padding might not be fully initialized/zeroed.
2. Conditional logic or branching that depends on potentially uninitialized variables
   or struct fields.
3. Allocation or initialization of complex data structures where uninitialized fields
   could be read later in reachable code paths.
4. Bounds checks, lengths, or logic in a way that allows surrounding code to access
   uninitialized bytes of existing buffers.

Set NeedsKMSAN=false IF:
- The code changes primarily risk out-of-bounds access, array overflows, NULL pointer
  dereferences, locking deadlocks, or use-after-free bugs (these are already caught
  by KASAN, LOCKDEP, or standard bug detectors).
- All stack/heap structures touched or introduced by the patch are fully zeroed
  or initialized (e.g. using = {0}, memset, kzalloc) before being read or copied.
- The patch does not introduce any risk of uninitialized memory usage or info-leaks.

Use your code access tools to inspect the surrounding code if necessary, then provide
detailed KMSANReasoning contrasting KASAN vs KMSAN applicability for this patch.
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

For your convenience, here is the diff of the changes:
commit 68936ee3d7a0fb9f82a7de6dbf2ebd29dcd9c164
Author: syz-cluster <triage@syzkaller.com>
Date:   Thu Aug 13 05:42:42 2026 +0000

    syz-cluster: applied patch under review

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index ddf6df7bee93b..9e9bd6c541baa 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3453,7 +3453,7 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
 		 * state which can lead to a load of wrong PDPTRs.
 		 */
 		if (CC(!load_pdptrs(vcpu, vcpu->arch.cr3)))
-			return false;
+			goto fail;
 	}
 
 
@@ -3469,7 +3469,7 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
 			vcpu->run->internal.suberror =
 				KVM_INTERNAL_ERROR_EMULATION;
 			vcpu->run->internal.ndata = 0;
-			return false;
+			goto fail;
 		}
 	}
 
@@ -3525,6 +3525,20 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
 		exec_controls_clearbit(vmx, CPU_BASED_USE_MSR_BITMAPS);
 
 	return true;
+
+fail:
+	/*
+	 * Re-arm the request so that KVM retries the mapping instead of running
+	 * L2 with a stale vmcs02.  Bailing here leaves the vCPU in guest mode
+	 * with vmcs02 loaded and its APIC-access, virtual-APIC and posted
+	 * interrupt descriptor addresses still pointing at the host pages that
+	 * were mapped for the *previous* nested VM-Enter, which have since been
+	 * unmapped and unpinned by nested_put_vmcs12_pages().  KVM returns to
+	 * userspace without leaving guest mode, so if userspace resumes the
+	 * vCPU, VM-Enter succeeds and hardware accesses those stale HPAs.
+	 */
+	kvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
+	return false;
 }
 
 static bool vmx_get_nested_state_pages(struct kvm_vcpu *vcpu)

gemini-3.1-pro-preview

null

null

							input: 2403
							output: 220
							thoughts: 710
						

**KMSAN Assessment: No Need for Dedicated Fuzzing**

Okay, so I've been looking at this patch for `nested_get_vmcs12_pages`. It's pretty straightforward, actually. Basically, instead of just bailing out with `false` when it fails, it now re-arms a request to retry the mapping. The comment makes it clear this is to prevent L2 from running with a stale `vmcs02`. The core problem? Hardware accessing host physical addresses (HPAs) that were valid *before* a nested VM-Enter, but are now garbage because they've been unmapped. This leads to a classic memory corruption scenario – use-after-free, effectively. Not ideal!

My initial reaction was to consider KMSAN (Kernel Memory Sanitizer). But hold on... this is all about stale *addresses*, not uninitialized memory. `kvm_make_request` just sets a bit in `vcpu->requests`. It's not creating new data, allocating memory, or leaking data to userspace. The fix itself is merely re-arming the request, and the underlying issue is stale pointers, not uninitialized memory. This is exactly what KASAN is built for.

So, KMSAN is a non-starter here. KASAN, or something similar, would be the right tool to catch this kind of use-after-free or invalid memory access bug. While KASAN might not catch the hardware's direct access to stale HPAs (depending on the instrumentation), KMSAN definitely won't, since it targets uninitialized memory.

Therefore, this patch doesn't warrant a dedicated KMSAN fuzzing session. It's a memory corruption issue, plain and simple, and should be handled with the appropriate tools.

{
  "KMSANReasoning": "The patch fixes an issue in KVM's nested virtualization where a failure in `nested_get_vmcs12_pages` could leave the vCPU in guest mode with stale host physical addresses (HPAs) mapped in vmcs02. If userspace resumed the vCPU, hardware could access these stale HPAs, leading to memory corruption or use-after-free-like behavior. The fix re-arms the `KVM_REQ_GET_NESTED_STATE_PAGES` request to ensure KVM retries the mapping.\n\nThis issue is related to stale pointers and invalid memory accesses, not uninitialized memory. The patch does not introduce any new data structures, allocations, or data copied to userspace that could expose uninitialized memory. Standard KASAN or other memory corruption detectors are more appropriate for catching use-after-free or invalid access bugs. Therefore, a dedicated KMSAN fuzzing session is not necessary.",
  "NeedsKMSAN": false
}

{
  "KMSANReasoning": "The patch fixes an issue in KVM's nested virtualization where a failure in `nested_get_vmcs12_pages` could leave the vCPU in guest mode with stale host physical addresses (HPAs) mapped in vmcs02. If userspace resumed the vCPU, hardware could access these stale HPAs, leading to memory corruption or use-after-free-like behavior. The fix re-arms the `KVM_REQ_GET_NESTED_STATE_PAGES` request to ensure KVM retries the mapping.\n\nThis issue is related to stale pointers and invalid memory accesses, not uninitialized memory. The patch does not introduce any new data structures, allocations, or data copied to userspace that could expose uninitialized memory. Standard KASAN or other memory corruption detectors are more appropriate for catching use-after-free or invalid access bugs. Therefore, a dedicated KMSAN fuzzing session is not necessary.",
  "NeedsKMSAN": false
}