From: Borislav Petkov <bp@alien8.de>
To: Andy Lutomirski <luto@kernel.org>
Cc: X86 ML <x86@kernel.org>,
jpa@kernelbug.mail.kapsi.fi, Dave Hansen <dave.hansen@intel.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] x86/fpu: Reset MXCSR to default in kernel_fpu_begin()
Date: Mon, 22 Jun 2020 19:09:08 +0200 [thread overview]
Message-ID: <20200622170908.GH32200@zn.tnic> (raw)
In-Reply-To: <CALCETrXZhFJGJA2h4zP743KYTtni-rQSUME8mtSYUdk1-ZTauQ@mail.gmail.com>
On Fri, Jun 19, 2020 at 11:01:44AM -0700, Andy Lutomirski wrote:
> On Fri, Jun 19, 2020 at 10:41 AM Borislav Petkov <bp@alien8.de> wrote:
> >
> > From: Petteri Aimonen <jpa@git.mail.kapsi.fi>
> >
> > Previously, kernel floating point code would run with the MXCSR control
> > register value last set by userland code by the thread that was active
> > on the CPU core just before kernel call. This could affect calculation
> > results if rounding mode was changed, or a crash if a FPU/SIMD exception
> > was unmasked.
> >
> > Restore MXCSR to the kernel's default value.
> >
> > [ bp: Carve out from a bigger patch by Petteri, add feature check, add
> > FNINIT call too (amluto). ]
>
> Acked-by: Andy Lutomirski <luto@kernel.org>
>
> but:
>
> shouldn't kernel_fpu_begin() end with a barrier()?
the "fninit" thing is already asm volatile or do you want the explicit
memory clobber of barrier?
If so, why?
The LDMXCSR and FNINIT have effect only on hardware state...
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2020-06-22 17:09 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-19 17:41 [PATCH 0/2] x86/FPU: FPU sanitization for in-kernel use Borislav Petkov
2020-06-19 17:41 ` [PATCH 1/2] x86/fpu: Reset MXCSR to default in kernel_fpu_begin() Borislav Petkov
2020-06-19 18:01 ` Andy Lutomirski
2020-06-22 17:09 ` Borislav Petkov [this message]
2020-06-22 18:33 ` Andy Lutomirski
2020-06-22 18:36 ` Petteri Aimonen
2020-06-22 18:38 ` Dave Hansen
2020-06-22 18:40 ` Andy Lutomirski
2020-06-22 18:59 ` Borislav Petkov
2020-06-19 17:41 ` [PATCH 2/2] selftests/fpu: Add an FPU selftest Borislav Petkov
2020-06-19 18:00 ` Andy Lutomirski
2020-06-22 17:12 ` Borislav Petkov
2020-06-22 18:26 ` Andy Lutomirski
2020-06-22 19:01 ` Borislav Petkov
[not found] ` <B4D00859-000A-4F8C-8CFB-45B9BBCCA16D@amacapital.net>
2020-06-23 10:28 ` Borislav Petkov
2020-06-23 18:22 ` Andy Lutomirski
2020-06-23 18:47 ` Borislav Petkov
2020-06-23 19:07 ` Nick Desaulniers
2020-06-23 19:13 ` Borislav Petkov
2020-06-23 20:58 ` Nick Desaulniers
2020-06-23 21:32 ` Borislav Petkov
2020-06-20 19:55 ` kernel test robot
2020-06-22 17:04 ` Borislav Petkov
2020-06-22 18:15 ` Nick Desaulniers
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