linux-kernel - Re: [PATCH 2/2] x86/fineibt: Poison ENDBR at +0

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20230621085104.GH2046280@hirez.programming.kicks-ass.net>
Date:   Wed, 21 Jun 2023 10:51:04 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Kees Cook <keescook@...omium.org>, x86@...nel.org,
        alyssa.milburn@...ux.intel.com, linux-kernel@...r.kernel.org,
        jpoimboe@...nel.org, joao@...rdrivepizza.com,
        tim.c.chen@...ux.intel.com
Subject: Re: [PATCH 2/2] x86/fineibt: Poison ENDBR at +0

On Tue, Jun 20, 2023 at 05:04:50PM -0700, Sami Tolvanen wrote:
> On Tue, Jun 20, 2023 at 2:55 PM Kees Cook <keescook@...omium.org> wrote:
> >
> > On Thu, Jun 15, 2023 at 09:35:48PM +0200, Peter Zijlstra wrote:
> > > Alyssa noticed that when building the kernel with CFI_CLANG+IBT and
> > > booting on IBT enabled hardware obtain FineIBT, the indirect functions
> > > look like:
> > >
> > >   __cfi_foo:
> > >       endbr64
> > >       subl    $hash, %r10d
> > >       jz      1f
> > >       ud2
> > >       nop
> > >   1:
> > >   foo:
> > >       endbr64
> > >
> > > This is because clang currently does not supress ENDBR emission for
> > > functions it provides a __cfi prologue symbol for.
> >
> > Should this be considered a bug in Clang?
> 
> The endbr is needed with KCFI if we have FineIBT disabled for some
> reason. There's some discussion here:
> 
> https://github.com/ClangBuiltLinux/linux/issues/1735
> 
> However, since the kernel handles FineIBT patching, it might be
> cleaner to let it also poison the extra endbr.

That's what I get for replying before reading all replies. Anyway, we're
in agreement.