linux-kernel - Re: [PATCH v3 1/3] x86/fpu: Make XCR0 accessors immune to unwanted compiler reordering

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: <ee82ed75-03f5-1962-6888-11491c9569c8@intel.com>
Date:   Fri, 1 Apr 2022 10:58:05 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Chang S. Bae" <chang.seok.bae@...el.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-pm@...r.kernel.org
Cc:     tglx@...utronix.de, dave.hansen@...ux.intel.com,
        peterz@...radead.org, bp@...en8.de, rafael@...nel.org,
        ravi.v.shankar@...el.com
Subject: Re: [PATCH v3 1/3] x86/fpu: Make XCR0 accessors immune to unwanted
 compiler reordering

On 3/24/22 19:22, Chang S. Bae wrote:
> Some old GCC versions (4.9.x and 5.x) have an issue that incorrectly
> reordering volatile asm statements with each other [1]. While this bug was
> fixed on later versions (8.1, 7.3, and 6.5), and the kernel's current XCR0
> read/write do not appear to be impacted, it is preventive to ensure them on
> the program order.

I thought you *actually* saw xgetbv() be reordered, though.  Was that on
a buggy compiler?