From: Kees Cook <keescook@chromium.org>
To: Matthias Kaehlcke <mka@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>,
"x86@kernel.org" <x86@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Grant Grundler <grundler@chromium.org>,
Greg Hackmann <ghackmann@google.com>,
Michael Davidson <md@google.com>
Subject: Re: [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication
Date: Mon, 1 May 2017 19:08:01 -0700 [thread overview]
Message-ID: <CAGXu5jLUj2egcZiC-TcmXQX6D8AuFSfRT+GNWdySNR6FRWaxNA@mail.gmail.com> (raw)
In-Reply-To: <20170501224741.133938-1-mka@chromium.org>
On Mon, May 1, 2017 at 3:47 PM, Matthias Kaehlcke <mka@chromium.org> wrote:
> The constraint "rm" allows the compiler to put mix_const into memory.
> When the input operand is a memory location mul needs an operand size
> suffix, since it can't infer the multiplication width from the operand.
>
> Add and use the _ASM_MUL macro which determines the operand size and
> resolves to the 'mul' instruction with the corresponding suffix.
>
> This fixes the following error when building with clang:
>
> CC arch/x86/lib/kaslr.o
> /tmp/kaslr-dfe1ad.s: Assembler messages:
> /tmp/kaslr-dfe1ad.s:182: Error: no instruction mnemonic suffix given and
> no register operands; can't size instruction
>
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Acked-by: Kees Cook <keescook@chromium.org>
Thanks for the v2!
-Kees
> ---
> Changes in v2:
> - updated commit message with additional details
>
> arch/x86/include/asm/asm.h | 1 +
> arch/x86/lib/kaslr.c | 3 ++-
> 2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
> index 7acb51c49fec..7a9df3beb89b 100644
> --- a/arch/x86/include/asm/asm.h
> +++ b/arch/x86/include/asm/asm.h
> @@ -32,6 +32,7 @@
> #define _ASM_ADD __ASM_SIZE(add)
> #define _ASM_SUB __ASM_SIZE(sub)
> #define _ASM_XADD __ASM_SIZE(xadd)
> +#define _ASM_MUL __ASM_SIZE(mul)
>
> #define _ASM_AX __ASM_REG(ax)
> #define _ASM_BX __ASM_REG(bx)
> diff --git a/arch/x86/lib/kaslr.c b/arch/x86/lib/kaslr.c
> index 121f59c6ee54..0c7fe444dcdd 100644
> --- a/arch/x86/lib/kaslr.c
> +++ b/arch/x86/lib/kaslr.c
> @@ -5,6 +5,7 @@
> * kernel starts. This file is included in the compressed kernel and
> * normally linked in the regular.
> */
> +#include <asm/asm.h>
> #include <asm/kaslr.h>
> #include <asm/msr.h>
> #include <asm/archrandom.h>
> @@ -79,7 +80,7 @@ unsigned long kaslr_get_random_long(const char *purpose)
> }
>
> /* Circular multiply for better bit diffusion */
> - asm("mul %3"
> + asm(_ASM_MUL "%3"
> : "=a" (random), "=d" (raw)
> : "a" (random), "rm" (mix_const));
> random += raw;
> --
> 2.13.0.rc1.294.g07d810a77f-goog
>
--
Kees Cook
Pixel Security
next prev parent reply other threads:[~2017-05-02 2:08 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-01 22:47 [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication Matthias Kaehlcke
2017-05-02 2:08 ` Kees Cook [this message]
2017-05-05 8:11 ` [tip:x86/urgent] x86/mm/kaslr: Use the _ASM_MUL macro for multiplication to work around Clang incompatibility tip-bot for Matthias Kaehlcke
2017-05-05 10:25 ` Peter Zijlstra
2017-05-05 17:50 ` Ingo Molnar
2017-05-05 18:22 ` Peter Zijlstra
2017-05-05 18:44 ` Matthias Kaehlcke
2017-05-05 19:30 ` Linus Torvalds
2017-05-05 20:36 ` Michael Davidson
2017-05-06 8:16 ` Peter Zijlstra
2017-05-07 15:42 ` hpa
2017-05-05 20:52 ` Matthias Kaehlcke
2017-05-06 9:57 ` Ingo Molnar
2017-05-05 19:37 ` hpa
2017-05-05 21:24 ` Matthias Kaehlcke
-- strict thread matches above, loose matches on Subject: below --
2017-04-26 20:55 [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication Matthias Kaehlcke
2017-04-26 21:00 ` hpa
2017-04-26 21:21 ` Kees Cook
2017-04-26 21:24 ` hpa
2017-04-26 21:29 ` Greg Hackmann
2017-04-29 21:23 ` H. Peter Anvin
2017-04-26 22:06 ` Kees Cook
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