On 12/03/26 2:00 pm, Sourabh Jain wrote:
update_backup_region_phdr() in file_load_64.c iterates over all the program headers in the kdump kernel’s elfcorehdr and updates the p_offset of the program header whose physical address starts at 0. However, the loop logic is incorrect because the program header pointer is not updated during iteration. Since elfcorehdr typically contains PT_NOTE entries first, the PT_LOAD program header with physical address 0 is never reached. As a result, its p_offset is not updated to point to the backup region. Because of this behavior, the capture kernel exports the first 64 KB of the crashed kernel’s memory at offset 0, even though that memory actually lives in the backup region. When a crash happens, purgatory copies the first 64 KB of the crashed kernel’s memory into the backup region so the capture kernel can safely use it. This has not caused problems so far because the first 64 KB is usually identical in both the crashed and capture kernels. However, this is just an assumption and is not guaranteed to always hold true. Fix update_backup_region_phdr() to correctly update the p_offset of the program header with a starting physical address of 0 by correcting the logic used to iterate over the program headers.
Thanks for fixing this. Looks good to me. Reviewed-by: Hari Bathini <[email protected]>
Fixes: cb350c1f1f86 ("powerpc/kexec_file: Prepare elfcore header for crashing kernel") Cc: Hari Bathini <[email protected]> Cc: Madhavan Srinivasan <[email protected]> Cc: Mahesh Salgaonkar <[email protected]> Cc: Michael Ellerman <[email protected]> Cc: Ritesh Harjani (IBM) <[email protected]> Cc: Shivang Upadhyay <[email protected]> Reviewed-by: Aditya Gupta <[email protected]> Signed-off-by: Sourabh Jain <[email protected]> --- arch/powerpc/kexec/file_load_64.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/powerpc/kexec/file_load_64.c b/arch/powerpc/kexec/file_load_64.c index e7ef8b2a2554..e631cf2eda2c 100644 --- a/arch/powerpc/kexec/file_load_64.c +++ b/arch/powerpc/kexec/file_load_64.c @@ -391,7 +391,7 @@ static void update_backup_region_phdr(struct kimage *image, Elf64_Ehdr *ehdr) unsigned int i;phdr = (Elf64_Phdr *)(ehdr + 1);- for (i = 0; i < ehdr->e_phnum; i++) { + for (i = 0; i < ehdr->e_phnum; i++, phdr++) { if (phdr->p_paddr == BACKUP_SRC_START) { phdr->p_offset = image->arch.backup_start; kexec_dprintk("Backup region offset updated to 0x%lx\n",
