From: Akshit Yadav <[email protected]> When a binary is patched or relocated such that the program header table is moved into a separate PT_LOAD segment (rather than sitting at the start of the first loadable segment), QEMU's AT_PHDR auxv entry becomes incorrect. The loader was computing AT_PHDR as load_addr + e_phoff, which assumes the headers are mapped 1:1 from file offset 0. This breaks when the headers are elsewhere.
The Linux kernel instead locates the PT_LOAD segment that contains e_phoff, then computes the in-memory address as p_vaddr + (e_phoff - p_offset). This correctly handles relocated headers. Fix by: 1. Add phdr_addr field to image_info to cache the resolved address. 2. Initialize to load_addr + e_phoff (fallback for headers outside any PT_LOAD). 3. In the PT_LOAD mapping loop, detect if the segment contains e_phoff and override with the segment-relative address. 4. Use info->phdr_addr for AT_PHDR instead of the incorrect formula. Signed-off-by: Akshit Yadav <[email protected]> Reviewed-by: Helge Deller <[email protected]> (cherry picked from commit 156e536a7b9700018aaa2437072c14e3376340a7) Signed-off-by: Michael Tokarev <[email protected]> diff --git a/linux-user/elfload.c b/linux-user/elfload.c index a791396ead..fdc84de4ba 100644 --- a/linux-user/elfload.c +++ b/linux-user/elfload.c @@ -2627,7 +2627,7 @@ static abi_ulong create_elf_tables(abi_ulong p, int argc, int envc, /* There must be exactly DLINFO_ITEMS entries here, or the assert * on info->auxv_len will trigger. */ - NEW_AUX_ENT(AT_PHDR, (abi_ulong)(info->load_addr + exec->e_phoff)); + NEW_AUX_ENT(AT_PHDR, (abi_ulong)(info->phdr_addr)); NEW_AUX_ENT(AT_PHENT, (abi_ulong)(sizeof (struct elf_phdr))); NEW_AUX_ENT(AT_PHNUM, (abi_ulong)(exec->e_phnum)); NEW_AUX_ENT(AT_PAGESZ, (abi_ulong)(TARGET_PAGE_SIZE)); @@ -3398,6 +3398,12 @@ static void load_elf_image(const char *image_name, const ImageSource *src, info->data_offset = load_bias; info->load_addr = load_addr; info->entry = ehdr->e_entry + load_bias; + /* + * Fallback for AT_PHDR if the program headers do not fall within + * any PT_LOAD segment (see the loop below, which overrides this with + * the correct in-memory address when a containing segment is found). + */ + info->phdr_addr = load_addr + ehdr->e_phoff; info->start_code = -1; info->end_code = 0; info->start_data = -1; @@ -3452,6 +3458,19 @@ static void load_elf_image(const char *image_name, const ImageSource *src, vaddr_ef = vaddr + eppnt->p_filesz; vaddr_em = vaddr + eppnt->p_memsz; + /* + * If this segment contains the program headers, record their + * in-memory address for AT_PHDR. This matches the kernel, which + * locates the headers via the containing PT_LOAD rather than + * assuming load_addr + e_phoff (false when the phdrs are not + * mapped 1:1 from file offset 0, e.g. relocated into their own + * segment by a binary patcher). + */ + if (eppnt->p_offset <= ehdr->e_phoff && + ehdr->e_phoff < eppnt->p_offset + eppnt->p_filesz) { + info->phdr_addr = vaddr + (ehdr->e_phoff - eppnt->p_offset); + } + /* * Some segments may be completely empty, with a non-zero p_memsz * but no backing file segment. diff --git a/linux-user/qemu.h b/linux-user/qemu.h index f2b16ef54b..a8ead75074 100644 --- a/linux-user/qemu.h +++ b/linux-user/qemu.h @@ -25,6 +25,7 @@ struct image_info { abi_ulong load_bias; abi_ulong load_addr; + abi_ulong phdr_addr; abi_ulong start_code; abi_ulong end_code; abi_ulong start_data; -- 2.47.3
