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Subject: Re: [PATCH] x86_32: add support for 64 bit __get_user()
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Wed, 09 Mar 2016 09:36:30 -0800
To: Benjamin LaHaise <bcrl@kvack.org>, Ingo Molnar <mingo@redhat.com>,
        Russell King <rmk@arm.linux.org.uk>
CC: Thomas Gleixner <tglx@linutronix.de>, x86@kernel.org,
        linux-kernel@vger.kernel.org
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On March 9, 2016 9:22:25 AM PST, Benjamin LaHaise <bcrl@kvack.org> wrote:
>The existing __get_user() implementation does not support fetching
>64 bit values on 32 bit x86.  Implement this in a way that does not 
>generate any incorrect warnings as cautioned by Russell King.  Test 
>code available at http://www.kvack.org/~bcrl/x86_32-get_user.tar .  
>
>Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>
>
>diff --git a/arch/x86/include/asm/uaccess.h
>b/arch/x86/include/asm/uaccess.h
>index a4a30e4..2d0607a 100644
>--- a/arch/x86/include/asm/uaccess.h
>+++ b/arch/x86/include/asm/uaccess.h
>@@ -333,7 +333,23 @@ do {									\
> } while (0)
> 
> #ifdef CONFIG_X86_32
>-#define __get_user_asm_u64(x, ptr, retval, errret)	(x) =
>__get_user_bad()
>+#define __get_user_asm_u64(x, addr, err, errret)			\
>+	asm volatile(ASM_STAC "\n"					\
>+		     "1:	movl %2,%%eax\n"			\
>+		     "2:	movl %3,%%edx\n"			\
>+		     "3: " ASM_CLAC "\n"				\
>+		     ".section .fixup,\"ax\"\n"				\
>+		     "4:	mov %4,%0\n"				\
>+		     "	xorl %%eax,%%eax\n"				\
>+		     "	xorl %%edx,%%edx\n"				\
>+		     "	jmp 3b\n"					\
>+		     ".previous\n"					\
>+		     _ASM_EXTABLE(1b, 4b)				\
>+		     _ASM_EXTABLE(2b, 4b)				\
>+		     : "=r" (err), "=A"(x)				\
>+		     : "m" (__m(addr)), "m" __m(((u32 *)(addr)) + 1),	\
>+		       "i" (errret), "0" (err))
>+
> #define __get_user_asm_ex_u64(x, ptr)			(x) = __get_user_bad()
> #else
> #define __get_user_asm_u64(x, ptr, retval, errret) \
>@@ -420,11 +436,20 @@ do {									\
> #define __get_user_nocheck(x, ptr, size)				\
> ({									\
> 	int __gu_err;							\
>-	unsigned long __gu_val;						\
>-	__uaccess_begin();						\
>-	__get_user_size(__gu_val, (ptr), (size), __gu_err, -EFAULT);	\
>-	__uaccess_end();						\
>-	(x) = (__force __typeof__(*(ptr)))__gu_val;			\
>+	if (size == 8) {						\
>+		unsigned long __gu_val[2];				\
>+		__gu_err = 0;						\
>+		__uaccess_begin();					\
>+		__get_user_asm_u64(__gu_val, ptr, __gu_err, -EFAULT);	\
>+		__uaccess_end();					\
>+		(x) = *(__force __typeof__((ptr)))__gu_val;		\
>+	} else {							\
>+		unsigned long __gu_val;					\
>+		__uaccess_begin();					\
>+		__get_user_size(__gu_val, (ptr), (size), __gu_err, -EFAULT); \
>+		__uaccess_end();					\
>+		(x) = (__force __typeof__(*(ptr)))__gu_val;		\
>+	}								\
> 	__builtin_expect(__gu_err, 0);					\
> })
> 

Weird.  I could swear we had already fixed this a few years ago.
-- 
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