LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	x86@kernel.org, joao@overdrivepizza.com, hjl.tools@gmail.com,
	andrew.cooper3@citrix.com, linux-kernel@vger.kernel.org,
	ndesaulniers@google.com, samitolvanen@google.com
Subject: Re: [RFC][PATCH 6/6] objtool: Add IBT validation / fixups
Date: Tue, 8 Feb 2022 21:09:00 -0800	[thread overview]
Message-ID: <20220209050900.vb676ocdrt6gsomf@treble> (raw)
In-Reply-To: <202202081542.F685EC23@keescook>

On Tue, Feb 08, 2022 at 03:43:27PM -0800, Kees Cook wrote:
> On Wed, Nov 24, 2021 at 11:30:37AM -0800, Josh Poimboeuf wrote:
> > 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.
> 
> Why have the kernel do that work at every boot when it can be known at
> link time?

True, but:

- The kernel is already doing several other flavors of boot-time
  self-patching.  IMO it's better to consolidate such craziness in one
  place (or a limited number of places) if we can.  It seems more
  robust, and limits confusion about who's patching what and when.

- Patching text at link time has pitfalls and I'd like to avoid (as much
  as reasonably possible) objtool having the ability to brick the
  kernel.

-- 
Josh


  reply	other threads:[~2022-02-09  5:27 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-22 17:03 [RFC][PATCH 0/6] x86: Kernel IBT beginnings Peter Zijlstra
2021-11-22 17:03 ` [RFC][PATCH 1/6] x86: Annotate _THIS_IP_ Peter Zijlstra
2021-11-23 13:53   ` Mark Rutland
2021-11-23 14:14     ` Peter Zijlstra
2021-11-24 18:18       ` Josh Poimboeuf
2021-11-22 17:03 ` [RFC][PATCH 2/6] x86: Base IBT bits Peter Zijlstra
2022-02-08 23:32   ` Kees Cook
2021-11-22 17:03 ` [RFC][PATCH 3/6] x86: Add ENDBR to IRET-to-Self Peter Zijlstra
2021-11-22 18:09   ` Peter Zijlstra
2022-02-08 23:33     ` Kees Cook
2021-11-22 17:03 ` [RFC][PATCH 4/6] objtool: Read the _THIS_IP_ hints Peter Zijlstra
2021-11-22 17:03 ` [RFC][PATCH 5/6] x86: Sprinkle ENDBR dust Peter Zijlstra
2021-11-23 14:00   ` Mark Rutland
2021-11-23 14:21     ` Peter Zijlstra
2022-02-08 23:38     ` Kees Cook
2021-11-22 17:03 ` [RFC][PATCH 6/6] objtool: Add IBT validation / fixups Peter Zijlstra
2021-11-24 19:30   ` Josh Poimboeuf
2022-02-08 23:43     ` Kees Cook
2022-02-09  5:09       ` Josh Poimboeuf [this message]
2022-02-09 11:41       ` Peter Zijlstra
2022-02-09 11:45         ` Peter Zijlstra
2021-12-24  2:05   ` joao
2022-02-08 23:42     ` Kees Cook
2022-02-09  2:21       ` Joao Moreira
2022-02-09  4:05         ` Kees Cook
2022-02-09  5:18           ` Joao Moreira
2022-02-11 13:38             ` Peter Zijlstra
2022-02-14 21:38               ` Sami Tolvanen
2022-02-14 22:25                 ` Peter Zijlstra
2022-02-15 16:56                   ` Sami Tolvanen
2022-02-15 20:03                     ` Kees Cook
2022-02-15 21:05                       ` Peter Zijlstra
2022-02-15 23:05                         ` Kees Cook
2022-02-15 23:38                           ` Joao Moreira
2022-02-16 12:24                         ` Peter Zijlstra
2022-02-15 20:53                     ` Peter Zijlstra
2022-02-15 22:45               ` Joao Moreira
2022-02-16  0:57               ` Andrew Cooper
2022-03-02  3:06               ` Peter Collingbourne
2022-03-02  3:32                 ` Joao Moreira
2022-06-08 17:53                 ` Fāng-ruì Sòng
2022-06-09  0:05                   ` Sami Tolvanen
2021-11-23  7:58 ` [RFC][PATCH 0/6] x86: Kernel IBT beginnings Christoph Hellwig
2021-11-23  9:02   ` Peter Zijlstra
2022-02-08 23:48 ` Kees Cook
2022-02-09  0:09 ` Nick Desaulniers

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20220209050900.vb676ocdrt6gsomf@treble \
    --to=jpoimboe@redhat.com \
    --cc=andrew.cooper3@citrix.com \
    --cc=hjl.tools@gmail.com \
    --cc=joao@overdrivepizza.com \
    --cc=keescook@chromium.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=ndesaulniers@google.com \
    --cc=peterz@infradead.org \
    --cc=samitolvanen@google.com \
    --cc=x86@kernel.org \
    --subject='Re: [RFC][PATCH 6/6] objtool: Add IBT validation / fixups' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).