linux-kernel - Re: [PATCH] x86/fpu/xstate: Fix PKRU covert channel

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: <c71199d1-93b3-ff51-f571-34d60cd36c1c@intel.com>
Date:   Thu, 31 Aug 2023 12:12:22 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jim Mattson <jmattson@...gle.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org
Cc:     Tavis Ormandy <taviso@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Kyle Huey <me@...ehuey.com>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Feng Tang <feng.tang@...el.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>
Subject: Re: [PATCH] x86/fpu/xstate: Fix PKRU covert channel

On 8/30/23 21:32, Jim Mattson wrote:
> When XCR0[9] is set, PKRU can be read and written from userspace with
> XSAVE and XRSTOR, even when CR4.PKE is clear.
> 
> Clear XCR0[9] when protection keys are disabled.
> 
> Reported-by: Tavis Ormandy <taviso@...gle.com>
> Signed-off-by: Jim Mattson <jmattson@...gle.com>

Is there any way to trigger this other than "nopku" on the command-line?

I'm not sure how scary this particular covert channel is, but it does
make sense to do this even if it's only to avoid wasting XSAVE space on
a feature that nobody can use (for things other than covert channels).

Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>