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

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Message-Id: <20240621100752.ea87e0868591dd3f49bbd271@linux-foundation.org>
Date: Fri, 21 Jun 2024 10:07:52 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Alexey Dobriyan <adobriyan@...il.com>
Cc: linux-kernel@...r.kernel.org, Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH] build-id: require program headers to be right after ELF
 header

On Fri, 21 Jun 2024 18:05:50 +0300 Alexey Dobriyan <adobriyan@...il.com> wrote:

> ELF spec doesn't require program header to be placed right after
> ELF header, but build-id code very much assumes such placement:
> 
> 	find_get_page(vma->vm_file->f_mapping, 0);
> 
> and later check against PAGE_SIZE.
> 
> Returns errors for now until someone rewrites build-id parser
> to be more correct.
>
> ...
>
> --- a/lib/buildid.c
> +++ b/lib/buildid.c
> @@ -73,6 +73,9 @@ static int get_build_id_32(const void *page_addr, unsigned char *build_id,
>  	Elf32_Phdr *phdr;
>  	int i;
>  
> +	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 +101,9 @@ static int get_build_id_64(const void *page_addr, unsigned char *build_id,
>  	Elf64_Phdr *phdr;
>  	int i;
>  
> +	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))

Well can we get comments in here eplaining the shortcoming?  That way
we're more likely to get a volunteer.

And please drop the braces?