Re: [GIT PULL] x86 fixes

[Linus Torvalds]

On Sat, 15 Jun 2024 at 01:13, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
>
>  - Fix the 8 bytes get_user() logic on x86-32

This is clearly a fix, but I think it's a bit ugly.

Instead of adding _more_ special cases for size 8, we could just remove them.

Making the 8-bit two-word versions just clear %ecx before doing the
first load means that all the exception handling becomes entirely
unified.

And then you can just use a nice macro for all the user accesses, and
the #ifdefs go away entirely for all exception handling. All that
remains is the "do I do a 'movq' or an xor and two movl's" question.

Something ENTIRELY UNTESTED like this, IOW.

I did check that it seemed to generate sane code on both 32-bit and
64-bit, but no _actual_ testing.

               Linus
 arch/x86/lib/getuser.S | 69 +++++++++++++++-----------------------------------
 1 file changed, 20 insertions(+), 49 deletions(-)

diff --git a/arch/x86/lib/getuser.S b/arch/x86/lib/getuser.S
index a1cb3a4e6742..a314622aa093 100644
--- a/arch/x86/lib/getuser.S
+++ b/arch/x86/lib/getuser.S
@@ -44,21 +44,23 @@
 	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
 .endm
 
+.macro UACCESS op src dst
+1:	\op \src,\dst
+	_ASM_EXTABLE_UA(1b, __get_user_handle_exception)
+.endm
+
+
 	.text
 SYM_FUNC_START(__get_user_1)
 	check_range size=1
 	ASM_STAC
-1:	movzbl (%_ASM_AX),%edx
+	UACCESS movzbl (%_ASM_AX),%edx
 	xor %eax,%eax
 	ASM_CLAC
 	RET
@@ -68,7 +70,7 @@ EXPORT_SYMBOL(__get_user_1)
 SYM_FUNC_START(__get_user_2)
 	check_range size=2
 	ASM_STAC
-2:	movzwl (%_ASM_AX),%edx
+	UACCESS movzwl (%_ASM_AX),%edx
 	xor %eax,%eax
 	ASM_CLAC
 	RET
@@ -78,7 +80,7 @@ EXPORT_SYMBOL(__get_user_2)
 SYM_FUNC_START(__get_user_4)
 	check_range size=4
 	ASM_STAC
-3:	movl (%_ASM_AX),%edx
+	UACCESS movl (%_ASM_AX),%edx
 	xor %eax,%eax
 	ASM_CLAC
 	RET
@@ -89,10 +91,11 @@ SYM_FUNC_START(__get_user_8)
 	check_range size=8
 	ASM_STAC
 #ifdef CONFIG_X86_64
-4:	movq (%_ASM_AX),%rdx
+	UACCESS movq (%_ASM_AX),%rdx
 #else
-4:	movl (%_ASM_AX),%edx
-5:	movl 4(%_ASM_AX),%ecx
+	xor %ecx,%ecx
+	UACCESS movl (%_ASM_AX),%edx
+	UACCESS movl 4(%_ASM_AX),%ecx
 #endif
 	xor %eax,%eax
 	ASM_CLAC
@@ -104,7 +107,7 @@ EXPORT_SYMBOL(__get_user_8)
 SYM_FUNC_START(__get_user_nocheck_1)
 	ASM_STAC
 	ASM_BARRIER_NOSPEC
-6:	movzbl (%_ASM_AX),%edx
+	UACCESS movzbl (%_ASM_AX),%edx
 	xor %eax,%eax
 	ASM_CLAC
 	RET
@@ -114,7 +117,7 @@ EXPORT_SYMBOL(__get_user_nocheck_1)
 SYM_FUNC_START(__get_user_nocheck_2)
 	ASM_STAC
 	ASM_BARRIER_NOSPEC
-7:	movzwl (%_ASM_AX),%edx
+	UACCESS movzwl (%_ASM_AX),%edx
 	xor %eax,%eax
 	ASM_CLAC
 	RET
@@ -124,7 +127,7 @@ EXPORT_SYMBOL(__get_user_nocheck_2)
 SYM_FUNC_START(__get_user_nocheck_4)
 	ASM_STAC
 	ASM_BARRIER_NOSPEC
-8:	movl (%_ASM_AX),%edx
+	UACCESS movl (%_ASM_AX),%edx
 	xor %eax,%eax
 	ASM_CLAC
 	RET
@@ -135,10 +138,11 @@ SYM_FUNC_START(__get_user_nocheck_8)
 	ASM_STAC
 	ASM_BARRIER_NOSPEC
 #ifdef CONFIG_X86_64
-9:	movq (%_ASM_AX),%rdx
+	UACCESS movq (%_ASM_AX),%rdx
 #else
-9:	movl (%_ASM_AX),%edx
-10:	movl 4(%_ASM_AX),%ecx
+	xor %ecx,%ecx
+	UACCESS movl (%_ASM_AX),%edx
+	UACCESS movl 4(%_ASM_AX),%ecx
 #endif
 	xor %eax,%eax
 	ASM_CLAC
@@ -154,36 +158,3 @@ SYM_CODE_START_LOCAL(__get_user_handle_exception)
 	mov $(-EFAULT),%_ASM_AX
 	RET
 SYM_CODE_END(__get_user_handle_exception)
-
-#ifdef CONFIG_X86_32
-SYM_CODE_START_LOCAL(__get_user_8_handle_exception)
-	ASM_CLAC
-.Lbad_get_user_8:
-	xor %edx,%edx
-	xor %ecx,%ecx
-	mov $(-EFAULT),%_ASM_AX
-	RET
-SYM_CODE_END(__get_user_8_handle_exception)
-#endif
-
-/* get_user */
-	_ASM_EXTABLE_UA(1b, __get_user_handle_exception)
-	_ASM_EXTABLE_UA(2b, __get_user_handle_exception)
-	_ASM_EXTABLE_UA(3b, __get_user_handle_exception)
-#ifdef CONFIG_X86_64
-	_ASM_EXTABLE_UA(4b, __get_user_handle_exception)
-#else
-	_ASM_EXTABLE_UA(4b, __get_user_8_handle_exception)
-	_ASM_EXTABLE_UA(5b, __get_user_8_handle_exception)
-#endif
-
-/* __get_user */
-	_ASM_EXTABLE_UA(6b, __get_user_handle_exception)
-	_ASM_EXTABLE_UA(7b, __get_user_handle_exception)
-	_ASM_EXTABLE_UA(8b, __get_user_handle_exception)
-#ifdef CONFIG_X86_64
-	_ASM_EXTABLE_UA(9b, __get_user_handle_exception)
-#else
-	_ASM_EXTABLE_UA(9b, __get_user_8_handle_exception)
-	_ASM_EXTABLE_UA(10b, __get_user_8_handle_exception)
-#endif