Re: [PATCH] x86_32: add support for 64 bit __get_user()

From: H. Peter Anvin
Date: Wed Mar 09 2016 - 12:39:18 EST


On March 9, 2016 9:22:25 AM PST, Benjamin LaHaise <bcrl@xxxxxxxxx> 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@xxxxxxxxx>
>
>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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