linux-hardening - [PATCH] x86/uaccess: Fix missed zeroing of ia32 u64 get

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Message-Id: <20240610210213.work.143-kees@kernel.org>
Date: Mon, 10 Jun 2024 14:02:27 -0700
From: Kees Cook <kees@...nel.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Kees Cook <kees@...nel.org>,
	David Gow <davidgow@...gle.com>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Sean Christopherson <seanjc@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnd Bergmann <arnd@...db.de>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Qiuxu Zhuo <qiuxu.zhuo@...el.com>,
	Nadav Amit <nadav.amit@...il.com>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Christian Brauner <brauner@...nel.org>,
	David Howells <dhowells@...hat.com>,
	Uros Bizjak <ubizjak@...il.com>,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: [PATCH] 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)

Reported-by: David Gow <davidgow@...gle.com>
Closes: https://lore.kernel.org/all/CABVgOSn=tb=Lj9SxHuT4_9MTjjKVxsq-ikdXC4kGHO4CfKVmGQ@mail.gmail.com
Fixes: b19b74bc99b1 ("x86/mm: Rework address range check in get_user() and put_user()")
Signed-off-by: Kees Cook <kees@...nel.org>
---
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: x86@...nel.org
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Sean Christopherson <seanjc@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Qiuxu Zhuo <qiuxu.zhuo@...el.com>
Cc: Nadav Amit <nadav.amit@...il.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>
---
 arch/x86/include/asm/uaccess.h | 4 ++--
 arch/x86/lib/getuser.S         | 6 +++++-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 0f9bab92a43d..3a7755c1a441 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/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);					\
diff --git a/arch/x86/lib/getuser.S b/arch/x86/lib/getuser.S
index 10d5ed8b5990..a1cb3a4e6742 100644
--- a/arch/x86/lib/getuser.S
+++ b/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
-- 
2.34.1