Use __put_user_goto in __put_user_size() and unsafe_put_user()

torvalds · torvalds · commit a959dc88f9c8 · 2019-01-04T18:15:25.000-08:00
This actually enables the __put_user_goto() functionality in
unsafe_put_user().

For an example of the effect of this, this is the code generated for the

        unsafe_put_user(signo, &amp;infop-&gt;si_signo, Efault);

in the waitid() system call:

	movl %ecx,(%rbx)        # signo, MEM[(struct __large_struct *)_2]

It's just one single store instruction, along with generating an
exception table entry pointing to the Efault label case in case that
instruction faults.

Before, we would generate this:

	xorl    %edx, %edx
	movl %ecx,(%rbx)        # signo, MEM[(struct __large_struct *)_3]
        testl   %edx, %edx
        jne     .L309

with the exception table generated for that 'mov' instruction causing us
to jump to a stub that set %edx to -EFAULT and then jumped back to the
'testl' instruction.

So not only do we now get rid of the extra code in the normal sequence,
we also avoid unnecessarily keeping that extra error register live
across it all.

Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
@@ -186,19 +186,14 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
 
 
 #ifdef CONFIG_X86_32
-#define __put_user_asm_u64(x, addr, err, errret)			\
-	asm volatile("\n"						\
-		     "1:	movl %%eax,0(%2)\n"			\
-		     "2:	movl %%edx,4(%2)\n"			\
-		     "3:"						\
-		     ".section .fixup,\"ax\"\n"				\
-		     "4:	movl %3,%0\n"				\
-		     "	jmp 3b\n"					\
-		     ".previous\n"					\
-		     _ASM_EXTABLE_UA(1b, 4b)				\
-		     _ASM_EXTABLE_UA(2b, 4b)				\
-		     : "=r" (err)					\
-		     : "A" (x), "r" (addr), "i" (errret), "0" (err))
+#define __put_user_goto_u64(x, addr, label)			\
+	asm_volatile_goto("\n"					\
+		     "1:	movl %%eax,0(%1)\n"		\
+		     "2:	movl %%edx,4(%1)\n"		\
+		     _ASM_EXTABLE_UA(1b, %l2)			\
+		     _ASM_EXTABLE_UA(2b, %l2)			\
+		     : : "A" (x), "r" (addr)			\
+		     : : label)
 
 #define __put_user_asm_ex_u64(x, addr)					\
 	asm volatile("\n"						\
@@ -213,8 +208,8 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
 	asm volatile("call __put_user_8" : "=a" (__ret_pu)	\
 		     : "A" ((typeof(*(ptr)))(x)), "c" (ptr) : "ebx")
 #else
-#define __put_user_asm_u64(x, ptr, retval, errret) \
-	__put_user_asm(x, ptr, retval, "q", "", "er", errret)
+#define __put_user_goto_u64(x, ptr, label) \
+	__put_user_goto(x, ptr, "q", "", "er", label)
 #define __put_user_asm_ex_u64(x, addr)	\
 	__put_user_asm_ex(x, addr, "q", "", "er")
 #define __put_user_x8(x, ptr, __ret_pu) __put_user_x(8, x, ptr, __ret_pu)
@@ -275,23 +270,21 @@ extern void __put_user_8(void);
 	__builtin_expect(__ret_pu, 0);				\
 })
 
-#define __put_user_size(x, ptr, size, retval, errret)			\
+#define __put_user_size(x, ptr, size, label)				\
 do {									\
-	retval = 0;							\
 	__chk_user_ptr(ptr);						\
 	switch (size) {							\
 	case 1:								\
-		__put_user_asm(x, ptr, retval, "b", "b", "iq", errret);	\
+		__put_user_goto(x, ptr, "b", "b", "iq", label);	\
 		break;							\
 	case 2:								\
-		__put_user_asm(x, ptr, retval, "w", "w", "ir", errret);	\
+		__put_user_goto(x, ptr, "w", "w", "ir", label);		\
 		break;							\
 	case 4:								\
-		__put_user_asm(x, ptr, retval, "l", "k", "ir", errret);	\
+		__put_user_goto(x, ptr, "l", "k", "ir", label);		\
 		break;							\
 	case 8:								\
-		__put_user_asm_u64((__typeof__(*ptr))(x), ptr, retval,	\
-				   errret);				\
+		__put_user_goto_u64((__typeof__(*ptr))(x), ptr, label);	\
 		break;							\
 	default:							\
 		__put_user_bad();					\
@@ -436,9 +429,12 @@ do {									\
 
 #define __put_user_nocheck(x, ptr, size)			\
 ({								\
-	int __pu_err;						\
+	__label__ __pu_label;					\
+	int __pu_err = -EFAULT;					\
 	__uaccess_begin();					\
-	__put_user_size((x), (ptr), (size), __pu_err, -EFAULT);	\
+	__put_user_size((x), (ptr), (size), __pu_label);	\
+	__pu_err = 0;						\
+__pu_label:							\
 	__uaccess_end();					\
 	__builtin_expect(__pu_err, 0);				\
 })
@@ -721,13 +717,8 @@ static __must_check inline bool user_access_begin(const void __user *ptr, size_t
 #define user_access_begin(a,b)	user_access_begin(a,b)
 #define user_access_end()	__uaccess_end()
 
-#define unsafe_put_user(x, ptr, err_label)					\
-do {										\
-	int __pu_err;								\
-	__typeof__(*(ptr)) __pu_val = (x);					\
-	__put_user_size(__pu_val, (ptr), sizeof(*(ptr)), __pu_err, -EFAULT);	\
-	if (unlikely(__pu_err)) goto err_label;					\
-} while (0)
+#define unsafe_put_user(x, ptr, label)	\
+	__put_user_size((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr)), label)
 
 #define unsafe_get_user(x, ptr, err_label)					\
 do {										\
