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

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

[Alexey Dobriyan]

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.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 lib/buildid.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- 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))

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

[Andrew Morton]

On Fri, 21 Jun 2024 18:05:50 +0300 Alexey Dobriyan <adobriyan@gmail.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?

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

[Alexey Dobriyan]

On Fri, Jun 21, 2024 at 10:07:52AM -0700, Andrew Morton wrote:
> On Fri, 21 Jun 2024 18:05:50 +0300 Alexey Dobriyan <adobriyan@gmail.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.

Sure.

> And please drop the braces?

Bracers are good. It took hundred years to drop -Wdeclaration-after-statement,
I hope to see mandatory bracers by 2050.

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

[Alexey Dobriyan]

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@gmail.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
+	 * 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))

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

[Jiri Olsa]

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@gmail.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@kernel.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))

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

[Andrii Nakryiko]

On Mon, Jun 24, 2024 at 4:23 AM Jiri Olsa <olsajiri@gmail.com> wrote:
>
> 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@gmail.com>
> > ---
> >
> >  lib/buildid.c |   14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> >

LGTM, but let's please route this through the bpf-next/master tree.
Can you please send it to bpf@vger.kernel.org?

Acked-by: Andrii Nakryiko <andrii@kernel.org>

> > --- 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@kernel.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))
>