Adding more mitigation options at exit-to-userspace for VMSCAPE would usually require a series of checks to decide which mitigation to use. In this case, the mitigation is done by calling a function, which is decided at boot. So, adding more feature flags and multiple checks can be avoided by using static_call() to the mitigating function. Replace the flag-based mitigation selector with a static_call(). This also frees the existing X86_FEATURE_IBPB_EXIT_TO_USER. Suggested-by: Dave Hansen Signed-off-by: Pawan Gupta --- arch/x86/Kconfig | 1 + arch/x86/include/asm/cpufeatures.h | 2 +- arch/x86/include/asm/entry-common.h | 7 +++---- arch/x86/include/asm/nospec-branch.h | 3 +++ arch/x86/kernel/cpu/bugs.c | 5 ++++- arch/x86/kvm/x86.c | 2 +- 6 files changed, 13 insertions(+), 7 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index fa3b616af03a2d50eaf5f922bc8cd4e08a284045..066f62f15e67e85fda0f3fd66acabad9a9794ff8 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2706,6 +2706,7 @@ config MITIGATION_TSA config MITIGATION_VMSCAPE bool "Mitigate VMSCAPE" depends on KVM + select HAVE_STATIC_CALL default y help Enable mitigation for VMSCAPE attacks. VMSCAPE is a hardware security diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index 4091a776e37aaed67ca93b0a0cd23cc25dbc33d4..02871318c999f94ec8557e5fb0b8fb299960d454 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -496,7 +496,7 @@ #define X86_FEATURE_TSA_SQ_NO (21*32+11) /* AMD CPU not vulnerable to TSA-SQ */ #define X86_FEATURE_TSA_L1_NO (21*32+12) /* AMD CPU not vulnerable to TSA-L1 */ #define X86_FEATURE_CLEAR_CPU_BUF_VM (21*32+13) /* Clear CPU buffers using VERW before VMRUN */ -#define X86_FEATURE_IBPB_EXIT_TO_USER (21*32+14) /* Use IBPB on exit-to-userspace, see VMSCAPE bug */ +/* Free */ #define X86_FEATURE_ABMC (21*32+15) /* Assignable Bandwidth Monitoring Counters */ #define X86_FEATURE_MSR_IMM (21*32+16) /* MSR immediate form instructions */ diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h index 78b143673ca72642149eb2dbf3e3e31370fe6b28..783e7cb50caeb6c6fc68e0a5c75ab43e75e37116 100644 --- a/arch/x86/include/asm/entry-common.h +++ b/arch/x86/include/asm/entry-common.h @@ -4,6 +4,7 @@ #include #include +#include #include #include @@ -94,10 +95,8 @@ static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs, */ choose_random_kstack_offset(rdtsc()); - /* Avoid unnecessary reads of 'x86_predictor_flush_exit_to_user' */ - if (cpu_feature_enabled(X86_FEATURE_IBPB_EXIT_TO_USER) && - this_cpu_read(x86_predictor_flush_exit_to_user)) { - write_ibpb(); + if (unlikely(this_cpu_read(x86_predictor_flush_exit_to_user))) { + static_call_cond(vmscape_predictor_flush)(); this_cpu_write(x86_predictor_flush_exit_to_user, false); } } diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index df60f9cf51b84e5b75e5db70713188d2e6ad0f5d..15a2fa8f2f48a066e102263513eff9537ac1d25f 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -540,6 +540,9 @@ static inline void indirect_branch_prediction_barrier(void) :: "rax", "rcx", "rdx", "memory"); } +#include +DECLARE_STATIC_CALL(vmscape_predictor_flush, write_ibpb); + /* The Intel SPEC CTRL MSR base value cache */ extern u64 x86_spec_ctrl_base; DECLARE_PER_CPU(u64, x86_spec_ctrl_current); diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 233594ede19bf971c999f4d3cc0f6f213002c16c..cbb3341b9a19f835738eda7226323d88b7e41e52 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -200,6 +200,9 @@ DEFINE_STATIC_KEY_FALSE(switch_mm_cond_l1d_flush); DEFINE_STATIC_KEY_FALSE(cpu_buf_vm_clear); EXPORT_SYMBOL_GPL(cpu_buf_vm_clear); +DEFINE_STATIC_CALL_NULL(vmscape_predictor_flush, write_ibpb); +EXPORT_STATIC_CALL_GPL(vmscape_predictor_flush); + #undef pr_fmt #define pr_fmt(fmt) "mitigations: " fmt @@ -3274,7 +3277,7 @@ static void __init vmscape_update_mitigation(void) static void __init vmscape_apply_mitigation(void) { if (vmscape_mitigation == VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER) - setup_force_cpu_cap(X86_FEATURE_IBPB_EXIT_TO_USER); + static_call_update(vmscape_predictor_flush, write_ibpb); } #undef pr_fmt diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 60123568fba85c8a445f9220d3f4a1d11fd0eb77..7e55ef3b3203a26be1a138c8fa838a8c5aae0125 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11396,7 +11396,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) * set for the CPU that actually ran the guest, and not the CPU that it * may migrate to. */ - if (cpu_feature_enabled(X86_FEATURE_IBPB_EXIT_TO_USER)) + if (static_call_query(vmscape_predictor_flush)) this_cpu_write(x86_predictor_flush_exit_to_user, true); /* -- 2.34.1