linux-kernel - Re: [GIT PULL] x86 fixes

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Date: Wed, 19 Jun 2024 17:36:06 +0200
From: Borislav Petkov <bp@...en8.de>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [GIT PULL] x86 fixes

On Sat, Jun 15, 2024 at 11:36:33AM -0700, Linus Torvalds wrote:
> 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.

Hohumm, looks ok to me. And running it a bit with selftests looks good too.

I productized it like this:

---
From: Linus Torvalds <torvalds@...ux-foundation.org>
Date: Wed, 19 Jun 2024 14:54:23 +0200
Subject: [PATCH] x86/uaccess: Improve the 8-byte getuser() case

Streamline the 8-byte case and drop the special handling. Use a macro
which hides the exception handling.

No functional changes.

Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
---
 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
-- 
2.43.0

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette