From: Andrey Rybainin <ryabinin.a.a@gmail.com>
To: Matthias Kaehlcke <mka@chromium.org>,
Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Chris J Arges <chris.j.arges@canonical.com>,
Borislav Petkov <bp@suse.de>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, linux-kernel@vger.kernel.org,
Douglas Anderson <dianders@chromium.org>,
Michael Davidson <md@google.com>,
Greg Hackmann <ghackmann@google.com>,
Nick Desaulniers <ndesaulniers@google.com>,
Stephen Hines <srhines@google.com>,
Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
Bernhard.Rosenkranzer@linaro.org
Subject: Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm"
Date: Thu, 13 Jul 2017 23:20:04 +0300 [thread overview]
Message-ID: <75850bb7-a60e-057d-d88b-afa0c79e94a0@gmail.com> (raw)
In-Reply-To: <20170713184748.GF95735@google.com>
On 07/13/2017 09:47 PM, Matthias Kaehlcke wrote:
> Thanks for your analysis!
>
>> What happens if you try the below patch instead of the revert? Any
>> chance the offending instruction goes away?
>>
>> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
>> index 11433f9..beac907 100644
>> --- a/arch/x86/include/asm/uaccess.h
>> +++ b/arch/x86/include/asm/uaccess.h
>> @@ -171,7 +171,7 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
>> might_fault(); \
>> asm volatile("call __get_user_%P4" \
>> : "=a" (__ret_gu), "=r" (__val_gu), "+r" (__sp) \
>> - : "0" (ptr), "i" (sizeof(*(ptr)))); \
>> + : "0" (ptr), "i" (sizeof(*(ptr))), "r" (__sp)); \
>> (x) = (__force __typeof__(*(ptr))) __val_gu; \
>> __builtin_expect(__ret_gu, 0); \
>> })
>
> The generated code is basically the same, only that now the value from
> the stack is stored in a register and written twice to RSP:
>
AFAIR clang works much better with global named registers.
Could you check if the patch bellow helps?
---
arch/x86/include/asm/uaccess.h | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index a059aac9e937..121204387978 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -157,15 +157,18 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
* Clang/LLVM cares about the size of the register, but still wants
* the base register for something that ends up being a pair.
*/
+
+register unsigned long __current_sp asm(_ASM_SP);
+
#define get_user(x, ptr) \
({ \
int __ret_gu; \
register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \
- register void *__sp asm(_ASM_SP); \
__chk_user_ptr(ptr); \
might_fault(); \
asm volatile("call __get_user_%P4" \
- : "=a" (__ret_gu), "=r" (__val_gu), "+r" (__sp) \
+ : "=a" (__ret_gu), "=r" (__val_gu), \
+ "+r" (__current_sp) \
: "0" (ptr), "i" (sizeof(*(ptr)))); \
(x) = (__force __typeof__(*(ptr))) __val_gu; \
__builtin_expect(__ret_gu, 0); \
--
2.13.0
next prev parent reply other threads:[~2017-07-13 20:22 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-12 21:27 [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Matthias Kaehlcke
2017-07-12 22:12 ` Josh Poimboeuf
2017-07-12 22:20 ` Matthias Kaehlcke
2017-07-12 22:35 ` Josh Poimboeuf
2017-07-12 22:36 ` Josh Poimboeuf
2017-07-12 23:22 ` Matthias Kaehlcke
2017-07-13 18:00 ` Josh Poimboeuf
2017-07-13 18:47 ` Matthias Kaehlcke
2017-07-13 19:25 ` Josh Poimboeuf
2017-07-13 19:38 ` Michael Davidson
2017-07-13 20:18 ` Josh Poimboeuf
2017-07-13 20:20 ` Andrey Rybainin [this message]
2017-07-13 20:34 ` Josh Poimboeuf
2017-07-13 21:12 ` Matthias Kaehlcke
2017-07-13 21:34 ` Josh Poimboeuf
2017-07-13 21:57 ` Matthias Kaehlcke
2017-07-19 17:46 ` Josh Poimboeuf
2017-07-19 21:50 ` Matthias Kaehlcke
2017-07-20 10:01 ` Andrey Ryabinin
2017-07-20 15:18 ` Josh Poimboeuf
2017-07-20 15:30 ` Andrey Ryabinin
2017-07-20 20:56 ` Josh Poimboeuf
2017-07-21 9:13 ` Andrey Ryabinin
2017-07-21 13:24 ` Josh Poimboeuf
2017-07-29 0:38 ` Matthias Kaehlcke
2017-07-29 0:55 ` Josh Poimboeuf
2017-07-29 0:58 ` Josh Poimboeuf
2017-07-29 1:06 ` Matthias Kaehlcke
2017-07-13 21:14 ` Matthias Kaehlcke
2017-07-13 21:25 ` Andrey Rybainin
2017-07-13 21:43 ` Matthias Kaehlcke
2017-07-13 21:52 ` Josh Poimboeuf
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