linux-kernel - Re: [PATCH] x86/ibt: Implement FineIBT

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Message-ID: <202210182217.486CBA50@keescook>
Date:   Tue, 18 Oct 2022 22:18:08 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Joao Moreira <joao@...rdrivepizza.com>, x86@...nel.org,
        Sami Tolvanen <samitolvanen@...gle.com>,
        linux-kernel@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH] x86/ibt: Implement FineIBT

On Tue, Oct 18, 2022 at 10:30:27PM +0200, Peter Zijlstra wrote:
> On Tue, Oct 18, 2022 at 01:17:28PM -0700, Joao Moreira wrote:
> > > 
> > > > Tangent: why are these nop instead of 0xcc? These bytes aren't
> > > > executed
> > > > ever are they?
> > > 
> > > Because that's what the compiler gets us through
> > > -fpatchable-function-entry.
> > 
> > Is it useful to get the compiler to emit 0xcc with
> > -fpatchable-function-entry under any circumstance? I can probably change
> > that quickly if needed/useful.
> 
> Having it emit 0xcc for the bytes in front of the symbol might be
> interesting. It would mean a few kernel changes, but nothing too hard.

The world is pretty different with endbr, but I still always need big
nop areas as giant "jump anywhere in here" targets. ;)

-- 
Kees Cook