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

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().

Link: https://lkml.kernel.org/r/d58bc281-6ca7-467a-9a64-40fa214bd63e@p183
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: Alexey Dobriyan

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))