Integrate the LUO with the KHO framework to enable passing LUO state across a kexec reboot. This patch implements the lifecycle integration with KHO: 1. Incoming State: During early boot (`early_initcall`), LUO checks if KHO is active. If so, it retrieves the "LUO" subtree, verifies the "luo-v1" compatibility string, and reads the `liveupdate-number` to track the update count. 2. Outgoing State: During late initialization (`late_initcall`), LUO allocates a new FDT for the next kernel, populates it with the basic header (compatible string and incremented update number), and registers it with KHO (`kho_add_subtree`). 3. Finalization: The `liveupdate_reboot()` notifier is updated to invoke `kho_finalize()`. This ensures that all memory segments marked for preservation are properly serialized before the kexec jump. Signed-off-by: Pasha Tatashin Reviewed-by: Pratyush Yadav --- include/linux/kho/abi/luo.h | 58 ++++++++++++ kernel/liveupdate/luo_core.c | 154 ++++++++++++++++++++++++++++++- kernel/liveupdate/luo_internal.h | 22 +++++ 3 files changed, 233 insertions(+), 1 deletion(-) create mode 100644 include/linux/kho/abi/luo.h create mode 100644 kernel/liveupdate/luo_internal.h diff --git a/include/linux/kho/abi/luo.h b/include/linux/kho/abi/luo.h new file mode 100644 index 000000000000..2099b51929e5 --- /dev/null +++ b/include/linux/kho/abi/luo.h @@ -0,0 +1,58 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +/* + * Copyright (c) 2025, Google LLC. + * Pasha Tatashin + */ + +/** + * DOC: Live Update Orchestrator ABI + * + * This header defines the stable Application Binary Interface used by the + * Live Update Orchestrator to pass state from a pre-update kernel to a + * post-update kernel. The ABI is built upon the Kexec HandOver framework + * and uses a Flattened Device Tree to describe the preserved data. + * + * This interface is a contract. Any modification to the FDT structure, node + * properties, compatible strings, or the layout of the `__packed` serialization + * structures defined here constitutes a breaking change. Such changes require + * incrementing the version number in the relevant `_COMPATIBLE` string to + * prevent a new kernel from misinterpreting data from an old kernel. + * + * Changes are allowed provided the compatibility version is incremented; + * however, backward/forward compatibility is only guaranteed for kernels + * supporting the same ABI version. + * + * FDT Structure Overview: + * The entire LUO state is encapsulated within a single KHO entry named "LUO". + * This entry contains an FDT with the following layout: + * + * .. code-block:: none + * + * / { + * compatible = "luo-v1"; + * liveupdate-number = <...>; + * }; + * + * Main LUO Node (/): + * + * - compatible: "luo-v1" + * Identifies the overall LUO ABI version. + * - liveupdate-number: u64 + * A counter tracking the number of successful live updates performed. + */ + +#ifndef _LINUX_KHO_ABI_LUO_H +#define _LINUX_KHO_ABI_LUO_H + +/* + * The LUO FDT hooks all LUO state for sessions, fds, etc. + * In the root it also carries "liveupdate-number" 64-bit property that + * corresponds to the number of live-updates performed on this machine. + */ +#define LUO_FDT_SIZE PAGE_SIZE +#define LUO_FDT_KHO_ENTRY_NAME "LUO" +#define LUO_FDT_COMPATIBLE "luo-v1" +#define LUO_FDT_LIVEUPDATE_NUM "liveupdate-number" + +#endif /* _LINUX_KHO_ABI_LUO_H */ diff --git a/kernel/liveupdate/luo_core.c b/kernel/liveupdate/luo_core.c index 30ad8836360b..9f9fe9a81b29 100644 --- a/kernel/liveupdate/luo_core.c +++ b/kernel/liveupdate/luo_core.c @@ -41,12 +41,26 @@ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt +#include +#include +#include #include +#include #include #include +#include +#include +#include +#include + +#include "kexec_handover_internal.h" +#include "luo_internal.h" static struct { bool enabled; + void *fdt_out; + void *fdt_in; + u64 liveupdate_num; } luo_global; static int __init early_liveupdate_param(char *buf) @@ -55,6 +69,129 @@ static int __init early_liveupdate_param(char *buf) } early_param("liveupdate", early_liveupdate_param); +static int __init luo_early_startup(void) +{ + phys_addr_t fdt_phys; + int err, ln_size; + const void *ptr; + + if (!kho_is_enabled()) { + if (liveupdate_enabled()) + pr_warn("Disabling liveupdate because KHO is disabled\n"); + luo_global.enabled = false; + return 0; + } + + /* Retrieve LUO subtree, and verify its format. */ + err = kho_retrieve_subtree(LUO_FDT_KHO_ENTRY_NAME, &fdt_phys); + if (err) { + if (err != -ENOENT) { + pr_err("failed to retrieve FDT '%s' from KHO: %pe\n", + LUO_FDT_KHO_ENTRY_NAME, ERR_PTR(err)); + return err; + } + + return 0; + } + + luo_global.fdt_in = phys_to_virt(fdt_phys); + err = fdt_node_check_compatible(luo_global.fdt_in, 0, + LUO_FDT_COMPATIBLE); + if (err) { + pr_err("FDT '%s' is incompatible with '%s' [%d]\n", + LUO_FDT_KHO_ENTRY_NAME, LUO_FDT_COMPATIBLE, err); + + return -EINVAL; + } + + ln_size = 0; + ptr = fdt_getprop(luo_global.fdt_in, 0, LUO_FDT_LIVEUPDATE_NUM, + &ln_size); + if (!ptr || ln_size != sizeof(luo_global.liveupdate_num)) { + pr_err("Unable to get live update number '%s' [%d]\n", + LUO_FDT_LIVEUPDATE_NUM, ln_size); + + return -EINVAL; + } + + luo_global.liveupdate_num = get_unaligned((u64 *)ptr); + pr_info("Retrieved live update data, liveupdate number: %lld\n", + luo_global.liveupdate_num); + + return 0; +} + +static int __init liveupdate_early_init(void) +{ + int err; + + err = luo_early_startup(); + if (err) { + luo_global.enabled = false; + luo_restore_fail("The incoming tree failed to initialize properly [%pe], disabling live update\n", + ERR_PTR(err)); + } + + return err; +} +early_initcall(liveupdate_early_init); + +/* Called during boot to create outgoing LUO fdt tree */ +static int __init luo_fdt_setup(void) +{ + const u64 ln = luo_global.liveupdate_num + 1; + void *fdt_out; + int err; + + fdt_out = kho_alloc_preserve(LUO_FDT_SIZE); + if (IS_ERR(fdt_out)) { + pr_err("failed to allocate/preserve FDT memory\n"); + return PTR_ERR(fdt_out); + } + + err = fdt_create(fdt_out, LUO_FDT_SIZE); + err |= fdt_finish_reservemap(fdt_out); + err |= fdt_begin_node(fdt_out, ""); + err |= fdt_property_string(fdt_out, "compatible", LUO_FDT_COMPATIBLE); + err |= fdt_property(fdt_out, LUO_FDT_LIVEUPDATE_NUM, &ln, sizeof(ln)); + err |= fdt_end_node(fdt_out); + err |= fdt_finish(fdt_out); + if (err) + goto exit_free; + + err = kho_add_subtree(LUO_FDT_KHO_ENTRY_NAME, fdt_out); + if (err) + goto exit_free; + luo_global.fdt_out = fdt_out; + + return 0; + +exit_free: + kho_unpreserve_free(fdt_out); + pr_err("failed to prepare LUO FDT: %d\n", err); + + return err; +} + +/* + * late initcall because it initializes the outgoing tree that is needed only + * once userspace starts using /dev/liveupdate. + */ +static int __init luo_late_startup(void) +{ + int err; + + if (!liveupdate_enabled()) + return 0; + + err = luo_fdt_setup(); + if (err) + luo_global.enabled = false; + + return err; +} +late_initcall(luo_late_startup); + /* Public Functions */ /** @@ -69,7 +206,22 @@ early_param("liveupdate", early_liveupdate_param); */ int liveupdate_reboot(void) { - return 0; + int err; + + if (!liveupdate_enabled()) + return 0; + + err = kho_finalize(); + if (err) { + pr_err("kho_finalize failed %d\n", err); + /* + * kho_finalize() may return libfdt errors, to aboid passing to + * userspace unknown errors, change this to EAGAIN. + */ + err = -EAGAIN; + } + + return err; } /** diff --git a/kernel/liveupdate/luo_internal.h b/kernel/liveupdate/luo_internal.h new file mode 100644 index 000000000000..8612687b2000 --- /dev/null +++ b/kernel/liveupdate/luo_internal.h @@ -0,0 +1,22 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +/* + * Copyright (c) 2025, Google LLC. + * Pasha Tatashin + */ + +#ifndef _LINUX_LUO_INTERNAL_H +#define _LINUX_LUO_INTERNAL_H + +#include + +/* + * Handles a deserialization failure: devices and memory is in unpredictable + * state. + * + * Continuing the boot process after a failure is dangerous because it could + * lead to leaks of private data. + */ +#define luo_restore_fail(__fmt, ...) panic(__fmt, ##__VA_ARGS__) + +#endif /* _LINUX_LUO_INTERNAL_H */ -- 2.52.0.460.gd25c4c69ec-goog