Re: [PATCH v2] build-id: require program headers to be right after ELF header

From: Jiri Olsa
Date: Mon Jun 24 2024 - 07:23:18 EST


ccing bpf list

On Fri, Jun 21, 2024 at 09:39:33PM +0300, Alexey Dobriyan wrote:
> Neither ELF spec not ELF loader require program header to be placed
> right after ELF header, but build-id code very much assumes such placement:
>
> See
>
> find_get_page(vma->vm_file->f_mapping, 0);
>
> line and checks against PAGE_SIZE.
>
> Returns errors for now until someone rewrites build-id parser
> to be more inline with load_elf_binary().
>
> Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
> ---
>
> lib/buildid.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> --- a/lib/buildid.c
> +++ b/lib/buildid.c
> @@ -73,6 +73,13 @@ static int get_build_id_32(const void *page_addr, unsigned char *build_id,
> Elf32_Phdr *phdr;
> int i;
>
> + /*
> + * FIXME

nit, FIXME is usually on the same line as the rest of the comment,
otherwise looks good

Reviewed-by: Jiri Olsa <jolsa@xxxxxxxxxx>

thanks,
jirka


> + * Neither ELF spec nor ELF loader require that program headers
> + * start immediately after ELF header.
> + */
> + if (ehdr->e_phoff != sizeof(Elf32_Ehdr))
> + return -EINVAL;
> /* only supports phdr that fits in one page */
> if (ehdr->e_phnum >
> (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr))
> @@ -98,6 +105,13 @@ static int get_build_id_64(const void *page_addr, unsigned char *build_id,
> Elf64_Phdr *phdr;
> int i;
>
> + /*
> + * FIXME
> + * Neither ELF spec nor ELF loader require that program headers
> + * start immediately after ELF header.
> + */
> + if (ehdr->e_phoff != sizeof(Elf64_Ehdr))
> + return -EINVAL;
> /* only supports phdr that fits in one page */
> if (ehdr->e_phnum >
> (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr))