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Date: Fri, 17 Feb 2017 09:03:26 -0800 From: Andy Lutomirski <luto@...capital.net> To: "H. Peter Anvin" <hpa@...or.com> Cc: Dmitry Safonov <dsafonov@...tuozzo.com>, "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 Mon, Feb 13, 2017 at 2:18 PM, <hpa@...or.com> wrote: > 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. Sure, but we should still apply Dmitry's patches first.
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