x86/uaccess: Fix missed zeroing of ia32 u64 get_user() range checking

When reworking the range checking for get_user(), the get_user_8() case
on 32-bit wasn't zeroing the high register. (The jump to bad_get_user_8
was accidentally dropped.) Restore the correct error handling
destination (and rename the jump to using the expected ".L" prefix).

While here, switch to using a named argument ("size") for the call
template ("%c4" to "%c[size]") as already used in the other call
templates in this file.

Found after moving the usercopy selftests to KUnit:

      # usercopy_test_invalid: EXPECTATION FAILED at
      lib/usercopy_kunit.c:278
      Expected val_u64 == 0, but
          val_u64 == -60129542144 (0xfffffff200000000)

Closes: https://lore.kernel.org/all/CABVgOSn=tb=Lj9SxHuT4_9MTjjKVxsq-ikdXC4kGHO4CfKVmGQ@mail.gmail.com
Fixes: b19b74b ("x86/mm: Rework address range check in get_user() and put_user()")
Reported-by: David Gow <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
Signed-off-by: Dave Hansen <[email protected]>
Reviewed-by: Kirill A. Shutemov <[email protected]>
Reviewed-by: Qiuxu Zhuo <[email protected]>
Tested-by: David Gow <[email protected]>
Link: https://lore.kernel.org/all/20240610210213.work.143-kees%40kernel.org

arch/x86/include/asm/uaccess.h

@@ -78,10 +78,10 @@ extern int __get_user_bad(void);
 	int __ret_gu;							\
 	register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX);		\
 	__chk_user_ptr(ptr);						\
-	asm volatile("call __" #fn "_%c4"				\
+	asm volatile("call __" #fn "_%c[size]"				\
 		     : "=a" (__ret_gu), "=r" (__val_gu),		\
 			ASM_CALL_CONSTRAINT				\
-		     : "0" (ptr), "i" (sizeof(*(ptr))));		\
+		     : "0" (ptr), [size] "i" (sizeof(*(ptr))));		\
 	instrument_get_user(__val_gu);					\
 	(x) = (__force __typeof__(*(ptr))) __val_gu;			\
 	__builtin_expect(__ret_gu, 0);					\

arch/x86/lib/getuser.S

@@ -44,7 +44,11 @@
 	or %rdx, %rax
 .else
 	cmp $TASK_SIZE_MAX-\size+1, %eax
+.if \size != 8
 	jae .Lbad_get_user
+.else
+	jae .Lbad_get_user_8
+.endif
 	sbb %edx, %edx		/* array_index_mask_nospec() */
 	and %edx, %eax
 .endif
@@ -154,7 +158,7 @@ SYM_CODE_END(__get_user_handle_exception)
 #ifdef CONFIG_X86_32
 SYM_CODE_START_LOCAL(__get_user_8_handle_exception)
 	ASM_CLAC
-bad_get_user_8:
+.Lbad_get_user_8:
 	xor %edx,%edx
 	xor %ecx,%ecx
 	mov $(-EFAULT),%_ASM_AX