linux-kernel - Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64

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Date:   Thu, 29 Nov 2018 15:42:22 +0100 (CET)
From:   Jiri Kosina <jikos@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Andy Lutomirski <luto@...capital.net>,
        Andy Lutomirski <luto@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jason Baron <jbaron@...mai.com>,
        David Laight <David.Laight@...lab.com>,
        Borislav Petkov <bp@...en8.de>, julia@...com, jeyu@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation
 for x86-64

On Thu, 29 Nov 2018, Peter Zijlstra wrote:

> > int3 isn’t IST anymore, so the int3 instruction conditionally 
> > subtracts 8 from RSP and then pushes SS, etc. So my email was 
> > obviously wrong wrt “cs”, but you’re still potentially overwriting the 
> > int3 IRET frame.
> 
> ARGH!..
> 
> can't we 'fix' that again? The alternative is moving that IRET-frame and
> fixing everything up, which is going to be fragile, ugly and such
> things more.
> 
> Commit d8ba61ba58c8 ("x86/entry/64: Don't use IST entry for #BP stack")
> doesn't list any strong reasons for why it should NOT be an IST.

It's CVE-2018-8897.

-- 
Jiri Kosina
SUSE Labs