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Subject[PATCH] x86: Add support for 64bit get_user() on x86-32
Date
From: Ville Syrjälä <ville.syrjala@linux.intel.com>

Implement __get_user_8() for x86-32. It will return the
64bit result in edx:eax register pair, and ecx is used
to pass in the address and return the error value.

For consistency, change the register assignment for all
other __get_user_x() variants, so that address is passed in
ecx/rcx, the error value is returned in ecx/rcx, and eax/rax
contains the actual value.

This is a partial refresh of a patch [1] by Jamie Lokier from
2004. Only the minimal changes to implement 64bit get_user()
were picked from the original patch.

[1] http://article.gmane.org/gmane.linux.kernel/198823

Cc: Jamie Lokier <jamie@shareable.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
arch/x86/include/asm/uaccess.h | 17 ++++++--
arch/x86/kernel/i386_ksyms_32.c | 1 +
arch/x86/lib/getuser.S | 82 ++++++++++++++++++++++++++------------
3 files changed, 69 insertions(+), 31 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 7ccf8d1..3f4387e 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -127,7 +127,7 @@ extern int __get_user_bad(void);

#define __get_user_x(size, ret, x, ptr) \
asm volatile("call __get_user_" #size \
- : "=a" (ret), "=d" (x) \
+ : "=c" (ret), "=a" (x) \
: "0" (ptr)) \

/* Careful: we have to cast the result to the type of the pointer
@@ -151,8 +151,11 @@ extern int __get_user_bad(void);
* On error, the variable @x is set to zero.
*/
#ifdef CONFIG_X86_32
-#define __get_user_8(__ret_gu, __val_gu, ptr) \
- __get_user_x(X, __ret_gu, __val_gu, ptr)
+#define __get_user_8(ret, x, ptr) \
+ asm volatile("call __get_user_8" \
+ : "=c" (ret), "=A" (x) \
+ : "0" (ptr)) \
+
#else
#define __get_user_8(__ret_gu, __val_gu, ptr) \
__get_user_x(8, __ret_gu, __val_gu, ptr)
@@ -162,6 +165,7 @@ extern int __get_user_bad(void);
({ \
int __ret_gu; \
unsigned long __val_gu; \
+ unsigned long long __val_gu8; \
__chk_user_ptr(ptr); \
might_fault(); \
switch (sizeof(*(ptr))) { \
@@ -175,13 +179,16 @@ extern int __get_user_bad(void);
__get_user_x(4, __ret_gu, __val_gu, ptr); \
break; \
case 8: \
- __get_user_8(__ret_gu, __val_gu, ptr); \
+ __get_user_8(__ret_gu, __val_gu8, ptr); \
break; \
default: \
__get_user_x(X, __ret_gu, __val_gu, ptr); \
break; \
} \
- (x) = (__typeof__(*(ptr)))__val_gu; \
+ if (sizeof(*(ptr)) == 8) \
+ (x) = (__typeof__(*(ptr)))__val_gu8; \
+ else \
+ (x) = (__typeof__(*(ptr)))__val_gu; \
__ret_gu; \
})

diff --git a/arch/x86/kernel/i386_ksyms_32.c b/arch/x86/kernel/i386_ksyms_32.c
index 9c3bd4a..0fa6912 100644
--- a/arch/x86/kernel/i386_ksyms_32.c
+++ b/arch/x86/kernel/i386_ksyms_32.c
@@ -26,6 +26,7 @@ EXPORT_SYMBOL(csum_partial_copy_generic);
EXPORT_SYMBOL(__get_user_1);
EXPORT_SYMBOL(__get_user_2);
EXPORT_SYMBOL(__get_user_4);
+EXPORT_SYMBOL(__get_user_8);

EXPORT_SYMBOL(__put_user_1);
EXPORT_SYMBOL(__put_user_2);
diff --git a/arch/x86/lib/getuser.S b/arch/x86/lib/getuser.S
index 156b9c8..38afef0 100644
--- a/arch/x86/lib/getuser.S
+++ b/arch/x86/lib/getuser.S
@@ -14,12 +14,11 @@
/*
* __get_user_X
*
- * Inputs: %[r|e]ax contains the address.
- * The register is modified, but all changes are undone
- * before returning because the C code doesn't know about it.
+ * Inputs: %[r|e]cx contains the address.
*
- * Outputs: %[r|e]ax is error code (0 or -EFAULT)
- * %[r|e]dx contains zero-extended value
+ * Outputs: %[r|e]cx is error code (0 or -EFAULT)
+ * %[r|e]ax contains zero-extended value
+ * %edx contains the high bits of the value for __get_user_8 on x86-32
*
*
* These functions should not modify any other registers,
@@ -38,12 +37,12 @@
.text
ENTRY(__get_user_1)
CFI_STARTPROC
- GET_THREAD_INFO(%_ASM_DX)
- cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
+ GET_THREAD_INFO(%_ASM_AX)
+ cmp TI_addr_limit(%_ASM_AX),%_ASM_CX
jae bad_get_user
ASM_STAC
-1: movzb (%_ASM_AX),%edx
- xor %eax,%eax
+1: movzb (%_ASM_CX),%eax
+ xor %ecx,%ecx
ASM_CLAC
ret
CFI_ENDPROC
@@ -51,14 +50,14 @@ ENDPROC(__get_user_1)

ENTRY(__get_user_2)
CFI_STARTPROC
- add $1,%_ASM_AX
+ add $1,%_ASM_CX
jc bad_get_user
- GET_THREAD_INFO(%_ASM_DX)
- cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
+ GET_THREAD_INFO(%_ASM_AX)
+ cmp TI_addr_limit(%_ASM_AX),%_ASM_CX
jae bad_get_user
ASM_STAC
-2: movzwl -1(%_ASM_AX),%edx
- xor %eax,%eax
+2: movzwl -1(%_ASM_CX),%eax
+ xor %ecx,%ecx
ASM_CLAC
ret
CFI_ENDPROC
@@ -66,14 +65,14 @@ ENDPROC(__get_user_2)

ENTRY(__get_user_4)
CFI_STARTPROC
- add $3,%_ASM_AX
+ add $3,%_ASM_CX
jc bad_get_user
- GET_THREAD_INFO(%_ASM_DX)
- cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
+ GET_THREAD_INFO(%_ASM_AX)
+ cmp TI_addr_limit(%_ASM_AX),%_ASM_CX
jae bad_get_user
ASM_STAC
-3: mov -3(%_ASM_AX),%edx
- xor %eax,%eax
+3: mov -3(%_ASM_CX),%eax
+ xor %ecx,%ecx
ASM_CLAC
ret
CFI_ENDPROC
@@ -82,14 +81,30 @@ ENDPROC(__get_user_4)
#ifdef CONFIG_X86_64
ENTRY(__get_user_8)
CFI_STARTPROC
- add $7,%_ASM_AX
+ add $7,%_ASM_CX
jc bad_get_user
- GET_THREAD_INFO(%_ASM_DX)
- cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
+ GET_THREAD_INFO(%_ASM_AX)
+ cmp TI_addr_limit(%_ASM_AX),%_ASM_CX
jae bad_get_user
ASM_STAC
-4: movq -7(%_ASM_AX),%_ASM_DX
- xor %eax,%eax
+4: movq -7(%_ASM_CX),%_ASM_AX
+ xor %ecx,%ecx
+ ASM_CLAC
+ ret
+ CFI_ENDPROC
+ENDPROC(__get_user_8)
+#else
+ENTRY(__get_user_8)
+ CFI_STARTPROC
+ add $7,%_ASM_CX
+ jc bad_get_user_8
+ GET_THREAD_INFO(%_ASM_AX)
+ cmp TI_addr_limit(%_ASM_AX),%_ASM_CX
+ jae bad_get_user_8
+ ASM_STAC
+4: mov -7(%_ASM_CX),%eax
+5: mov -3(%_ASM_CX),%edx
+ xor %ecx,%ecx
ASM_CLAC
ret
CFI_ENDPROC
@@ -98,16 +113,31 @@ ENDPROC(__get_user_8)

bad_get_user:
CFI_STARTPROC
- xor %edx,%edx
- mov $(-EFAULT),%_ASM_AX
+ xor %eax,%eax
+ mov $(-EFAULT),%_ASM_CX
ASM_CLAC
ret
CFI_ENDPROC
END(bad_get_user)

+#ifdef CONFIG_X86_32
+bad_get_user_8:
+ CFI_STARTPROC
+ xor %eax,%eax
+ xor %edx,%edx
+ mov $(-EFAULT),%_ASM_CX
+ ASM_CLAC
+ ret
+ CFI_ENDPROC
+END(bad_get_user_8)
+#endif
+
_ASM_EXTABLE(1b,bad_get_user)
_ASM_EXTABLE(2b,bad_get_user)
_ASM_EXTABLE(3b,bad_get_user)
#ifdef CONFIG_X86_64
_ASM_EXTABLE(4b,bad_get_user)
+#else
+ _ASM_EXTABLE(4b,bad_get_user_8)
+ _ASM_EXTABLE(5b,bad_get_user_8)
#endif
--
1.7.8.6
--
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