linux-kernel - Re: [PATCH 1/2] x86/cfi: Fix ret_from

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Message-ID: <20230621201357.GQ38236@hirez.programming.kicks-ass.net>
Date:   Wed, 21 Jun 2023 22:13:57 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     x86@...nel.org, alyssa.milburn@...ux.intel.com,
        linux-kernel@...r.kernel.org, samitolvanen@...gle.com,
        jpoimboe@...nel.org, joao@...rdrivepizza.com,
        tim.c.chen@...ux.intel.com
Subject: Re: [PATCH 1/2] x86/cfi: Fix ret_from_fork indirect calls

On Wed, Jun 21, 2023 at 08:33:56PM +0200, Peter Zijlstra wrote:
> On Wed, Jun 21, 2023 at 08:16:59PM +0200, Peter Zijlstra wrote:
> > On Wed, Jun 21, 2023 at 11:08:46AM -0700, Kees Cook wrote:
> > 
> > > Ah yeah, it should be direct-called only. I keep forgetting about the
> > > endbr removal pass.
> > > 
> > > > I can't seem to manage to have it clobber it's __cfi hash value. Ideally
> > > > we'd have an attribute to force the thing to 0 or something.
> > > 
> > > Doesn't objtool have logic to figure out this is only ever
> > > direct-called?
> > 
> > It does; let me also use that same thing to clobber the kCFI hashes for
> > these functions.
> 
> Completely untested... gotta go put the kids to bed. I'll try later.

With a few minor edits it seems to actually boot too. I'll go write up a
Changelog tomorrow. Now I've got to discover how Drizzt's adventure
continues ;-)