Re: [RFC][PATCH 6/6] objtool: Add IBT validation / fixups

Josh Poimboeuf
2021-11-24T19:30:45Z

On Mon, Nov 22, 2021 at 06:03:07PM +0100, Peter Zijlstra wrote:
> +static int validate_ibt_reloc(struct objtool_file *file, struct reloc *reloc, char **name)
> +{
> + struct instruction *dest;
> + struct section *sec;
> + unsigned long off;
> +
> + sec = reloc->sym->sec;
> + off = reloc->sym->offset + reloc->addend;
> +
> + dest = find_insn(file, sec, off);
> + if (!dest)
> + return 0;
> +
> + if (name && dest->func)
> + *name = dest->func->name;

I think these checks can be further narrowed down by only looking for
X86_64_64 relocs.

> + list_for_each_entry(insn, &file->endbr_list, call_node) {
> + if (ibt_seal) {
> + elf_write_insn(file->elf, insn->sec,
> + insn->offset, insn->len,
> + arch_nop_insn(insn->len));
> + }

Like the retpoline rewriting, I'd much rather have objtool create
annotations which the kernel can then read and patch itself.

e.g. have '.ibt.direct_call_sites' and '.ibt.unused_endbr_insns'
sections.

--
Josh