From: Joe Lawrence joe.lawrence@redhat.com
commit dc02368164bd0ec603e3f5b3dd8252744a667b8a upstream.
Commit e31694e0a7a7 ("objtool: Don't make .altinstructions writable") aligned objtool-created and kernel-created .altinstructions section flags, but there remains a minor discrepency in their use of a section entry size: objtool sets one while the kernel build does not.
While sh_entsize of sizeof(struct alt_instr) seems intuitive, this small deviation can cause failures with external tooling (kpatch-build).
Fix this by creating new .altinstructions sections with sh_entsize of 0 and then later updating sec->sh_size as alternatives are added to the section. An added benefit is avoiding the data descriptor and buffer created by elf_create_section(), but previously unused by elf_add_alternative().
Fixes: 9bc0bb50727c ("objtool/x86: Rewrite retpoline thunk calls") Signed-off-by: Joe Lawrence joe.lawrence@redhat.com Reviewed-by: Miroslav Benes mbenes@suse.cz Signed-off-by: Josh Poimboeuf jpoimboe@redhat.com Link: https://lore.kernel.org/r/20210822225037.54620-2-joe.lawrence@redhat.com Cc: Andy Lavr andy.lavr@gmail.com Cc: Peter Zijlstra peterz@infradead.org Cc: x86@kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Ben Hutchings ben@decadent.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- tools/objtool/arch/x86/decode.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/tools/objtool/arch/x86/decode.c +++ b/tools/objtool/arch/x86/decode.c @@ -611,7 +611,7 @@ static int elf_add_alternative(struct el sec = find_section_by_name(elf, ".altinstructions"); if (!sec) { sec = elf_create_section(elf, ".altinstructions", - SHF_ALLOC, size, 0); + SHF_ALLOC, 0, 0);
if (!sec) { WARN_ELF("elf_create_section");