Commit 60592fb6 authored May 12, 2023 by Fangrui Song Committed by Kees Cook May 16, 2023

coredump, vmcore: Set p_align to 4 for PT_NOTE

Tools like readelf/llvm-readelf use p_align to parse a PT_NOTE program
header as an array of 4-byte entries or 8-byte entries. Currently, there
are workarounds[1] in place for Linux to treat p_align==0 as 4. However,
it would be more appropriate to set the correct alignment so that tools
do not have to rely on guesswork. FreeBSD coredumps set p_align to 4 as
well.

[1]: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=82ed9683ec099d8205dc499ac84febc975235af6
[2]: https://reviews.llvm.org/D150022



Signed-off-by: Fangrui Song <maskray@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230512022528.3430327-1-maskray@google.com

parent f1fcbaa1

fs/binfmt_elf.c

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -1517,7 +1517,7 @@ static void fill_elf_note_phdr(struct elf_phdr *phdr, int sz, loff_t offset)
	phdr->p_filesz = sz;		phdr->p_filesz = sz;
	phdr->p_memsz = 0;		phdr->p_memsz = 0;
	phdr->p_flags = 0;		phdr->p_flags = 0;
	phdr->p_align = 0;		phdr->p_align = 4;
	}		}

	static void fill_note(struct memelfnote note, const char name, int type,		static void fill_note(struct memelfnote note, const char name, int type,

fs/binfmt_elf_fdpic.c

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -1269,7 +1269,7 @@ static inline void fill_elf_note_phdr(struct elf_phdr *phdr, int sz, loff_t offs
	phdr->p_filesz = sz;		phdr->p_filesz = sz;
	phdr->p_memsz = 0;		phdr->p_memsz = 0;
	phdr->p_flags = 0;		phdr->p_flags = 0;
	phdr->p_align = 0;		phdr->p_align = 4;
	return;		return;
	}		}

fs/proc/vmcore.c

+2 −2

Original line number	Original line	Diff line number	Diff line
	@@ -877,7 +877,7 @@ static int __init merge_note_headers_elf64(char elfptr, size_t elfsz,
	phdr.p_offset = roundup(note_off, PAGE_SIZE);		phdr.p_offset = roundup(note_off, PAGE_SIZE);
	phdr.p_vaddr = phdr.p_paddr = 0;		phdr.p_vaddr = phdr.p_paddr = 0;
	phdr.p_filesz = phdr.p_memsz = phdr_sz;		phdr.p_filesz = phdr.p_memsz = phdr_sz;
	phdr.p_align = 0;		phdr.p_align = 4;

	/* Add merged PT_NOTE program header*/		/* Add merged PT_NOTE program header*/
	tmp = elfptr + sizeof(Elf64_Ehdr);		tmp = elfptr + sizeof(Elf64_Ehdr);
	@@ -1068,7 +1068,7 @@ static int __init merge_note_headers_elf32(char elfptr, size_t elfsz,
	phdr.p_offset = roundup(note_off, PAGE_SIZE);		phdr.p_offset = roundup(note_off, PAGE_SIZE);
	phdr.p_vaddr = phdr.p_paddr = 0;		phdr.p_vaddr = phdr.p_paddr = 0;
	phdr.p_filesz = phdr.p_memsz = phdr_sz;		phdr.p_filesz = phdr.p_memsz = phdr_sz;
	phdr.p_align = 0;		phdr.p_align = 4;

	/* Add merged PT_NOTE program header*/		/* Add merged PT_NOTE program header*/
	tmp = elfptr + sizeof(Elf32_Ehdr);		tmp = elfptr + sizeof(Elf32_Ehdr);