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From: Andy Lutomirski <luto@kernel.org>
To: Borislav Petkov <bp@alien8.de>
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 2/2] selftests/fpu: Add an FPU selftest
Date: Fri, 19 Jun 2020 11:00:28 -0700	[thread overview]
Message-ID: <CALCETrXXzt8WZMs3dsReCJ5wdF3zhxFmUtGnmdCgV7_exFUKKQ@mail.gmail.com> (raw)
In-Reply-To: <20200619174127.22304-3-bp@alien8.de>

On Fri, Jun 19, 2020 at 10:41 AM Borislav Petkov <bp@alien8.de> wrote:
>
> From: Petteri Aimonen <jpa@git.mail.kapsi.fi>
>
> Add a selftest for the usage of FPU code in kernel mode.
>
> Currently only implemented for x86. In the future, kernel FPU testing
> could be unified between the different architectures supporting it.

Acked-by: Andy Lutomirski <luto@kernel.org>

except:

> +#
> +# CFLAGS for compiling floating point code inside the kernel. x86/Makefile turns
> +# off the generation of FPU/SSE* instructions for kernel proper but FPU_FLAGS
> +# get appended last to CFLAGS and thus override those previous compiler options.
> +#
> +FPU_CFLAGS += -mhard-float -msse
> +ifdef CONFIG_CC_IS_GCC
> +  ifeq ($(call cc-ifversion, -lt, 0701, y), y)
> +    # Stack alignment mismatch, proceed with caution.
> +    # GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3
> +    # (8B stack alignment).
> +    FPU_CFLAGS += -mpreferred-stack-boundary=4
> +  else
> +    FPU_CFLAGS += -msse2
> +  endif
> +endif

This should be cc-option, not cc-ifversion, I think.  But maybe we
should consider dropping the problematic GCC version instead?  The old
GCC versions with stack alignment problems are seriously problematic
for x86 kernels, and I don't really trust kernels built with them.

  reply	other threads:[~2020-06-19 18:00 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
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 [this message]
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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