linux-kernel - Re: [PATCHv3] x86/selftests: add clobbers for int80 on x86

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 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]

Date:   Mon, 13 Feb 2017 14:18:36 -0800
From:   hpa@...or.com
To:     Andy Lutomirski <luto@...capital.net>,
        Dmitry Safonov <dsafonov@...tuozzo.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Shuah Khan <shuah@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...e.de>, X86 ML <x86@...nel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCHv3] x86/selftests: add clobbers for int80 on x86_64

On February 13, 2017 11:06:04 AM PST, Andy Lutomirski <luto@...capital.net> wrote:
>On Mon, Feb 13, 2017 at 2:13 AM, Dmitry Safonov
><dsafonov@...tuozzo.com> wrote:
>> Kernel erases R8..R11 registers prior returning to userspace
>> from int80: https://lkml.org/lkml/2009/10/1/164
>>
>> GCC can reuse this registers and doesn't expect them to change
>> during syscall invocation. I met this kind of bug in CRIU once
>> gcc 6.1 and clang stored local variables in those registers
>> and the kernel zerofied them during syscall:
>>
>https://github.com/xemul/criu/commit/990d33f1a1cdd17bca6c2eb059ab3be2564f7fa2
>>
>> By that reason I suggest to add those registers to clobbers
>> in selftests.  Also, as notted by Andy - removed unneeded clobber
>> for flags in int 0x80 inline asm.
>
>Acked-by: Andy Lutomirski <luto@...nel.org>
>
>Although these days we could preserve these regs in the kernel at the
>cost of (I think) 4 bytes of text and zero runtime overhead.
>
>--Andy

If we can do so that cheaply I think we should.
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.