x86: remove more uaccess_32.h complexity

I'm looking at trying to possibly merge the 32-bit and 64-bit versions
of the x86 uaccess.h implementation, but first this needs to be cleaned
up.

For example, the 32-bit version of "__copy_from_user_inatomic()" is
mostly the special cases for the constant size, and it's actually almost
never relevant.  Most users aren't actually using a constant size
anyway, and the few cases that do small constant copies are better off
just using __get_user() instead.

So get rid of the unnecessary complexity.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit bd28b14591b98f696bc9f94c5ba2e598ca487dfd)
Signed-off-by: Alex Shi <alex.shi@linaro.org>

Author: torvalds

arch/x86/include/asm/uaccess_32.h

@@ -65,32 +65,6 @@ __copy_to_user(void __user *to, const void *from, unsigned long n)
 static __always_inline unsigned long
 __copy_from_user_inatomic(void *to, const void __user *from, unsigned long n)
 {
-	/* Avoid zeroing the tail if the copy fails..
-	 * If 'n' is constant and 1, 2, or 4, we do still zero on a failure,
-	 * but as the zeroing behaviour is only significant when n is not
-	 * constant, that shouldn't be a problem.
-	 */
-	if (__builtin_constant_p(n)) {
-		unsigned long ret;
-
-		switch (n) {
-		case 1:
-			__uaccess_begin();
-			__get_user_size(*(u8 *)to, from, 1, ret, 1);
-			__uaccess_end();
-			return ret;
-		case 2:
-			__uaccess_begin();
-			__get_user_size(*(u16 *)to, from, 2, ret, 2);
-			__uaccess_end();
-			return ret;
-		case 4:
-			__uaccess_begin();
-			__get_user_size(*(u32 *)to, from, 4, ret, 4);
-			__uaccess_end();
-			return ret;
-		}
-	}
 	return __copy_from_user_ll_nozero(to, from, n);
 }
 

kernel/events/uprobes.c

@@ -1692,8 +1692,7 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr)
 	int result;
 
 	pagefault_disable();
-	result = __copy_from_user_inatomic(&opcode, (void __user*)vaddr,
-							sizeof(opcode));
+	result = __get_user(opcode, (uprobe_opcode_t __user *)vaddr);
 	pagefault_enable();
 
 	if (likely(result == 0))

kernel/futex.c

@@ -681,7 +681,7 @@ static int get_futex_value_locked(u32 *dest, u32 __user *from)
 	int ret;
 
 	pagefault_disable();
-	ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
+	ret = __get_user(*dest, from);
 	pagefault_enable();
 
 	return ret ? -EFAULT : 0;

mm/maccess.c

@@ -96,8 +96,7 @@ long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)
 	pagefault_disable();
 
 	do {
-		ret = __copy_from_user_inatomic(dst++,
-						(const void __user __force *)src++, 1);
+		ret = __get_user(*dst++, (const char __user __force *)src++);
 	} while (dst[-1] && ret == 0 && src - unsafe_addr < count);
 
 	dst[-1] = '\0';