From 94f9cef0f51c0cb14495dab315266c0a3ae4ce9a Mon Sep 17 00:00:00 2001 From: Michal Clapinski Date: Tue, 2 Jun 2026 14:33:11 +0200 Subject: [PATCH 1/2] kexec_file: skip checksum verification when safe Checksum verification is needed 1. for crash kernels. In a crash, we can't be sure the kernel is intact. 2. if we're worried about relocating the kernel into a region used by some DMA that wasn't properly cancelled. If KHO is enabled then relocations will happen to KHO scratch, which is free from DMA regions. If we used CMA to allocate segments then relocations are not going to happen at all. Therefore, we can safely disable checksum verification in both of those cases. Instead of adding a new variable to purgatory, just skip adding regions and save the default value of SHA256 hash. Saves ~250ms on my 4.0 GHz CPU. This is an important saving for the live-update project. Signed-off-by: Michal Clapinski Reviewed-by: Pratyush Yadav (Google) Reviewed-by: Pasha Tatashin Acked-by: Baoquan He Link: https://patch.msgid.link/20260602123311.1841746-1-mclapinski@google.com Signed-off-by: Pasha Tatashin Signed-off-by: Mike Rapoport (Microsoft) --- kernel/kexec_file.c | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c index 2bfbb2d144e6..59fb9d71e9d8 100644 --- a/kernel/kexec_file.c +++ b/kernel/kexec_file.c @@ -27,6 +27,7 @@ #include #include #include +#include #include "kexec_internal.h" #ifdef CONFIG_KEXEC_SIG @@ -798,6 +799,16 @@ int kexec_add_buffer(struct kexec_buf *kbuf) return 0; } +static bool kexec_only_cma_segments(struct kimage *image) +{ + for (int i = 0; i < image->nr_segments; i++) { + if (!image->segment_cma[i]) + return false; + } + + return true; +} + /* Calculate and store the digest of segments */ static int kexec_calculate_store_digests(struct kimage *image) { @@ -822,6 +833,21 @@ static int kexec_calculate_store_digests(struct kimage *image) sha256_init(&sctx); + /* + * If KHO is enabled, the destinations are located in KHO scratch. + * KHO scratch can only contain early boot allocations and movable + * allocations. That means there is no risk of memory corruption by + * uncancelled DMA. + * + * If all segments were loaded into contiguous memory, there will be no + * relocations at all, so also no risk of corruption. + */ + if (image->type != KEXEC_TYPE_CRASH && + (kho_is_enabled() || kexec_only_cma_segments(image))) { + pr_debug("disabling checksum verification in purgatory\n"); + goto skip_checksum; + } + for (j = i = 0; i < image->nr_segments; i++) { struct kexec_segment *ksegment; @@ -867,6 +893,7 @@ static int kexec_calculate_store_digests(struct kimage *image) j++; } +skip_checksum: sha256_final(&sctx, digest); ret = kexec_purgatory_get_set_symbol(image, "purgatory_sha_regions", From 6a673b6c419a5b5bf7457f33b80a77f842057066 Mon Sep 17 00:00:00 2001 From: Thomas Huth Date: Fri, 19 Jun 2026 18:06:54 +0200 Subject: [PATCH 2/2] kexec: Replace __ASSEMBLY__ with __ASSEMBLER__ in header file While the GCC and Clang compilers already define __ASSEMBLER__ automatically when compiling assembly code, __ASSEMBLY__ is a macro that only gets defined by the Makefiles in the kernel. This can be very confusing when switching between userspace and kernelspace coding, or when dealing with uapi headers that rather should use __ASSEMBLER__ instead. So let's standardize now on the __ASSEMBLER__ macro that is provided by the compilers. Signed-off-by: Thomas Huth Acked-by: Pratyush Yadav Link: https://patch.msgid.link/20260619160654.75980-1-thuth@redhat.com Signed-off-by: Mike Rapoport (Microsoft) --- include/linux/kexec.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/kexec.h b/include/linux/kexec.h index 8a22bc9b8c6c..0af8ae4fdd08 100644 --- a/include/linux/kexec.h +++ b/include/linux/kexec.h @@ -13,7 +13,7 @@ #define IND_SOURCE (1 << IND_SOURCE_BIT) #define IND_FLAGS (IND_DESTINATION | IND_INDIRECTION | IND_DONE | IND_SOURCE) -#if !defined(__ASSEMBLY__) +#if !defined(__ASSEMBLER__) #include #include