linux-kernel - Re: [PATCH v2 5/8] x86/speculation: Add basic support for IBPB

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 for Android: free password hash cracker in your pocket

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

Date:   Sun, 21 Jan 2018 19:31:00 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Borislav Petkov <bp@...en8.de>,
        KarimAllah Ahmed <karahmed@...zon.com>
Cc:     arjan@...ux.intel.com, tglx@...utronix.de, karahmed@...zon.de,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        tim.c.chen@...ux.intel.com, peterz@...radead.org,
        pbonzini@...hat.com, ak@...ux.intel.com,
        torvalds@...ux-foundation.org, gregkh@...ux-foundation.org
Subject: Re: [PATCH v2 5/8] x86/speculation: Add basic support for IBPB

On Sun, 2018-01-21 at 20:01 +0100, Borislav Petkov wrote:
> 
> so execution runs directly into the MSR write and the JMP is gone.
> 
> So I don't see indirect branches anywhere...

Wait until the wind changes.

Congratulations, you've just turned a potential GCC missed optimisation
into a kernel bug. We don't *care* that it's unlikely that GCC will
miss that optimisation. The point is that it doesn't *have* to do it,
and we don't *check*.

cf. https://lkml.org/lkml/2018/1/12/176

... after which Peter went off and implemented that check, which is all
fine and dandy but let's not rely on backporting that too.
Download attachment "smime.p7s" of type "application/x-pkcs7-signature" (5213 bytes)