x86-32: Add support for 64bit get_user()

Implement __get_user_8() for x86-32. It will return the
64-bit 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.

[ hpa: I modified the patch so that it does NOT change the calling
  conventions for the existing callsites, this also means that the code
  is completely unchanged for 64 bits.

  Instead, continue to use eax for address input/error output and use
  the ecx:edx register pair for the output. ]

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

Originally-by: Jamie Lokier <jamie@shareable.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link:
http://lkml.kernel.org/r/1355312043-11467-1-git-send-email-ville.syrjala@linux.intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

3 files changed, 48 insertions, 9 deletions

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 1709801d18ec..1e963267d44e 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -151,8 +151,15 @@ 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)		      \
+do {						      \
+	register unsigned long long __xx asm("%edx"); \
+	asm volatile("call __get_user_8"	      \
+		     : "=a" (ret), "=r" (__xx)	      \
+		     : "0" (ptr));		      \
+	(x) = __xx;				      \
+} while (0)
+
 #else
 #define __get_user_8(__ret_gu, __val_gu, ptr)				\
 		__get_user_x(8, __ret_gu, __val_gu, ptr)
@@ -162,6 +169,7 @@ 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 +183,16 @@ 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 9c3bd4a2050e..0fa69127209a 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 156b9c804670..d3bf9f99ca77 100644
--- a/arch/x86/lib/getuser.S
+++ b/arch/x86/lib/getuser.S
@@ -15,11 +15,10 @@
  * __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.
  *
  * Outputs:	%[r|e]ax is error code (0 or -EFAULT)
  *		%[r|e]dx contains zero-extended value
+ *		%ecx contains the high half for 32-bit __get_user_8
  *
  *
  * These functions should not modify any other registers,
@@ -79,22 +78,35 @@ ENTRY(__get_user_4)
 	CFI_ENDPROC
 ENDPROC(__get_user_4)
 
-#ifdef CONFIG_X86_64
 ENTRY(__get_user_8)
 	CFI_STARTPROC
+#ifdef CONFIG_X86_64
 	add $7,%_ASM_AX
 	jc bad_get_user
 	GET_THREAD_INFO(%_ASM_DX)
 	cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
-	jae	bad_get_user
+	jae bad_get_user
 	ASM_STAC
 4:	movq -7(%_ASM_AX),%_ASM_DX
 	xor %eax,%eax
 	ASM_CLAC
 	ret
+#else
+	add $7,%_ASM_AX
+	jc bad_get_user_8
+	GET_THREAD_INFO(%_ASM_DX)
+	cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
+	jae bad_get_user_8
+	ASM_STAC
+4:	mov -7(%_ASM_AX),%edx
+5:	mov -3(%_ASM_AX),%ecx
+	xor %eax,%eax
+	ASM_CLAC
+	ret
+#endif
 	CFI_ENDPROC
 ENDPROC(__get_user_8)
-#endif
+
 
 bad_get_user:
 	CFI_STARTPROC
@@ -105,9 +117,24 @@ bad_get_user:
 	CFI_ENDPROC
 END(bad_get_user)
 
+#ifdef CONFIG_X86_32
+bad_get_user_8:
+	CFI_STARTPROC
+	xor %edx,%edx
+	xor %ecx,%ecx
+	mov $(-EFAULT),%_ASM_AX
+	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