It is invalid for KHO metadata or preserved memory regions to be located within the KHO scratch area, as this area is overwritten when the next kernel is loaded, and used early in boot by the next kernel. This can lead to memory corruption.
Adds checks to kho_preserve_* and KHO's internal metadata allocators (xa_load_or_alloc, new_chunk) to verify that the physical address of the memory does not overlap with any defined scratch region. If an overlap is detected, the operation will fail and a WARN_ON is triggered. To avoid performance overhead in production kernels, these checks are enabled only when CONFIG_KEXEC_HANDOVER_DEBUG is selected.
Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com --- kernel/liveupdate/Kconfig | 8 ++++ kernel/liveupdate/Makefile | 1 + kernel/liveupdate/kexec_handover.c | 52 ++++++++++++++------- kernel/liveupdate/kexec_handover_debug.c | 25 ++++++++++ kernel/liveupdate/kexec_handover_internal.h | 9 ++++ 5 files changed, 78 insertions(+), 17 deletions(-) create mode 100644 kernel/liveupdate/kexec_handover_debug.c
diff --git a/kernel/liveupdate/Kconfig b/kernel/liveupdate/Kconfig index cea287842475..851d1a22b4c5 100644 --- a/kernel/liveupdate/Kconfig +++ b/kernel/liveupdate/Kconfig @@ -27,4 +27,12 @@ config KEXEC_HANDOVER_DEBUGFS Also, enables inspecting the KHO fdt trees with the debugfs binary blobs.
+config KEXEC_HANDOVER_DEBUG + bool "Enable Kexec Handover debug checks" + depends on KEXEC_HANDOVER_DEBUGFS + help + This option enables extra sanity checks for the Kexec Handover + subsystem. Since, KHO performance is crucial in live update + scenarios and the extra code might be adding overhead it is + only optionally enabled. endmenu diff --git a/kernel/liveupdate/Makefile b/kernel/liveupdate/Makefile index fcdf163b4b0e..f52ce1ebcf86 100644 --- a/kernel/liveupdate/Makefile +++ b/kernel/liveupdate/Makefile @@ -1,4 +1,5 @@ # SPDX-License-Identifier: GPL-2.0
obj-$(CONFIG_KEXEC_HANDOVER) += kexec_handover.o +obj-$(CONFIG_KEXEC_HANDOVER_DEBUG) += kexec_handover_debug.o obj-$(CONFIG_KEXEC_HANDOVER_DEBUGFS) += kexec_handover_debugfs.o diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c index c87d00c40c82..ebfc31814d16 100644 --- a/kernel/liveupdate/kexec_handover.c +++ b/kernel/liveupdate/kexec_handover.c @@ -8,6 +8,7 @@
#define pr_fmt(fmt) "KHO: " fmt
+#include <linux/cleanup.h> #include <linux/cma.h> #include <linux/count_zeros.h> #include <linux/kexec.h> @@ -131,26 +132,26 @@ static struct kho_out kho_out = {
static void *xa_load_or_alloc(struct xarray *xa, unsigned long index, size_t sz) { - void *elm, *res; + void *res = xa_load(xa, index);
- elm = xa_load(xa, index); - if (elm) - return elm; + if (res) + return res; + + void *elm __free(kfree) = kzalloc(sz, GFP_KERNEL);
- elm = kzalloc(sz, GFP_KERNEL); if (!elm) return ERR_PTR(-ENOMEM);
+ if (WARN_ON(kho_scratch_overlap(virt_to_phys(elm), sz))) + return ERR_PTR(-EINVAL); + res = xa_cmpxchg(xa, index, NULL, elm, GFP_KERNEL); if (xa_is_err(res)) - res = ERR_PTR(xa_err(res)); - - if (res) { - kfree(elm); + return ERR_PTR(xa_err(res)); + else if (res) return res; - }
- return elm; + return no_free_ptr(elm); }
static void __kho_unpreserve_order(struct kho_mem_track *track, unsigned long pfn, @@ -350,15 +351,19 @@ static_assert(sizeof(struct khoser_mem_chunk) == PAGE_SIZE); static struct khoser_mem_chunk *new_chunk(struct khoser_mem_chunk *cur_chunk, unsigned long order) { - struct khoser_mem_chunk *chunk; + struct khoser_mem_chunk *chunk __free(kfree) = NULL;
chunk = kzalloc(PAGE_SIZE, GFP_KERNEL); if (!chunk) - return NULL; + return ERR_PTR(-ENOMEM); + + if (WARN_ON(kho_scratch_overlap(virt_to_phys(chunk), PAGE_SIZE))) + return ERR_PTR(-EINVAL); + chunk->hdr.order = order; if (cur_chunk) KHOSER_STORE_PTR(cur_chunk->hdr.next, chunk); - return chunk; + return no_free_ptr(chunk); }
static void kho_mem_ser_free(struct khoser_mem_chunk *first_chunk) @@ -379,14 +384,17 @@ static int kho_mem_serialize(struct kho_out *kho_out) struct khoser_mem_chunk *chunk = NULL; struct kho_mem_phys *physxa; unsigned long order; + int ret = -ENOMEM;
xa_for_each(&kho_out->track.orders, order, physxa) { struct kho_mem_phys_bits *bits; unsigned long phys;
chunk = new_chunk(chunk, order); - if (!chunk) + if (IS_ERR(chunk)) { + ret = PTR_ERR(chunk); goto err_free; + }
if (!first_chunk) first_chunk = chunk; @@ -396,8 +404,10 @@ static int kho_mem_serialize(struct kho_out *kho_out)
if (chunk->hdr.num_elms == ARRAY_SIZE(chunk->bitmaps)) { chunk = new_chunk(chunk, order); - if (!chunk) + if (IS_ERR(chunk)) { + ret = PTR_ERR(chunk); goto err_free; + } }
elm = &chunk->bitmaps[chunk->hdr.num_elms]; @@ -414,7 +424,7 @@ static int kho_mem_serialize(struct kho_out *kho_out)
err_free: kho_mem_ser_free(first_chunk); - return -ENOMEM; + return ret; }
static void __init deserialize_bitmap(unsigned int order, @@ -737,6 +747,9 @@ int kho_preserve_folio(struct folio *folio) const unsigned int order = folio_order(folio); struct kho_mem_track *track = &kho_out.track;
+ if (WARN_ON(kho_scratch_overlap(pfn << PAGE_SHIFT, PAGE_SIZE << order))) + return -EINVAL; + return __kho_preserve_order(track, pfn, order); } EXPORT_SYMBOL_GPL(kho_preserve_folio); @@ -784,6 +797,11 @@ int kho_preserve_pages(struct page *page, unsigned int nr_pages) unsigned long failed_pfn = 0; int err = 0;
+ if (WARN_ON(kho_scratch_overlap(start_pfn << PAGE_SHIFT, + nr_pages << PAGE_SHIFT))) { + return -EINVAL; + } + while (pfn < end_pfn) { const unsigned int order = min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn)); diff --git a/kernel/liveupdate/kexec_handover_debug.c b/kernel/liveupdate/kexec_handover_debug.c new file mode 100644 index 000000000000..7986dcc63047 --- /dev/null +++ b/kernel/liveupdate/kexec_handover_debug.c @@ -0,0 +1,25 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * kexec_handover_debug.c - kexec handover optional debug functionality + * Copyright (C) 2025 Google LLC, Pasha Tatashin pasha.tatashin@soleen.com + */ + +#define pr_fmt(fmt) "KHO: " fmt + +#include "kexec_handover_internal.h" + +bool kho_scratch_overlap(phys_addr_t phys, size_t size) +{ + phys_addr_t scratch_start, scratch_end; + unsigned int i; + + for (i = 0; i < kho_scratch_cnt; i++) { + scratch_start = kho_scratch[i].addr; + scratch_end = kho_scratch[i].addr + kho_scratch[i].size - 1; + + if (phys <= scratch_end && (phys + size) > scratch_start) + return true; + } + + return false; +} diff --git a/kernel/liveupdate/kexec_handover_internal.h b/kernel/liveupdate/kexec_handover_internal.h index b3fc1957affa..92798346fa5a 100644 --- a/kernel/liveupdate/kexec_handover_internal.h +++ b/kernel/liveupdate/kexec_handover_internal.h @@ -44,4 +44,13 @@ static inline void kho_debugfs_fdt_remove(struct kho_debugfs *dbg, void *fdt) { } #endif /* CONFIG_KEXEC_HANDOVER_DEBUGFS */
+#ifdef CONFIG_KEXEC_HANDOVER_DEBUG +bool kho_scratch_overlap(phys_addr_t phys, size_t size); +#else +static inline bool kho_scratch_overlap(phys_addr_t phys, size_t size) +{ + return false; +} +#endif /* CONFIG_KEXEC_HANDOVER_DEBUG */ + #endif /* LINUX_KEXEC_HANDOVER_INTERNAL_H */