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

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Date: Mon, 24 Jun 2024 13:23:00 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Alexey Dobriyan <adobriyan@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
	bpf@...r.kernel.org
Subject: Re: [PATCH v2] build-id: require program headers to be right after
 ELF header

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@...il.com>
> ---
> 
>  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@...nel.org>

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))