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Date: Tue,  7 Aug 2018 03:22:56 +0200
From: Jann Horn <jannh@...gle.com>
To: Kees Cook <keescook@...omium.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org, 
	kernel-hardening@...ts.openwall.com, jannh@...gle.com
Cc: linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>, dvyukov@...gle.com
Subject: [RFC PATCH 1/2] x86: WARN() when uaccess helpers fault on kernel addresses

There have been multiple kernel vulnerabilities that permitted userspace to
pass completely unchecked pointers through to userspace accessors:

 - the waitid() bug - commit 96ca579a1ecc ("waitid(): Add missing
   access_ok() checks")
 - the sg/bsg read/write APIs
 - the infiniband read/write APIs

These don't happen all that often, but when they do happen, it is hard to
test for them properly; and it is probably also hard to discover them with
fuzzing. Even when an unmapped kernel address is supplied to such buggy
code, it just returns -EFAULT instead of doing a proper BUG() or at least
WARN().

This patch attempts to make such misbehaving code a bit more visible by
WARN()ing in the pagefault handler code when a userspace accessor causes
#PF on a kernel address and the current context isn't whitelisted.

Signed-off-by: Jann Horn <jannh@...gle.com>
---
This is a hacky, quickly thrown-together PoC to see what people think
about the basic idea. Does it look like a sensible change? Or would it
be better, for example, to instead expand the KASan hooks in the
usercopy logic to also look at the "user" pointer if it points to
kernelspace? That would have the advantage of also catching heap
overflows properly...

I'm not really happy with all the plumbing in my patch; I wonder whether
there's a way around introducing _ASM_EXTABLE_UA() for user accessors?

arch/x86/include/asm/asm.h          |  10 ++-
 arch/x86/include/asm/extable.h      |   3 +-
 arch/x86/include/asm/fpu/internal.h |   6 +-
 arch/x86/include/asm/futex.h        |   6 +-
 arch/x86/include/asm/uaccess.h      |  22 ++---
 arch/x86/kernel/cpu/mcheck/mce.c    |   2 +-
 arch/x86/kernel/kprobes/core.c      |   2 +-
 arch/x86/kernel/traps.c             |   6 +-
 arch/x86/lib/checksum_32.S          |   4 +-
 arch/x86/lib/copy_user_64.S         |  90 ++++++++++----------
 arch/x86/lib/csum-copy_64.S         |   6 +-
 arch/x86/lib/getuser.S              |  12 +--
 arch/x86/lib/putuser.S              |  10 +--
 arch/x86/lib/usercopy_32.c          | 126 ++++++++++++++--------------
 arch/x86/lib/usercopy_64.c          |   4 +-
 arch/x86/mm/extable.c               |  67 ++++++++++++---
 arch/x86/mm/fault.c                 |   2 +-
 include/linux/sched.h               |   2 +
 mm/maccess.c                        |   6 ++
 19 files changed, 221 insertions(+), 165 deletions(-)

diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index 990770f9e76b..38f44a773adf 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -130,6 +130,9 @@
 # define _ASM_EXTABLE(from, to)					\
 	_ASM_EXTABLE_HANDLE(from, to, ex_handler_default)
 
+# define _ASM_EXTABLE_UA(from, to)				\
+	_ASM_EXTABLE_HANDLE(from, to, ex_handler_uaccess)
+
 # define _ASM_EXTABLE_FAULT(from, to)				\
 	_ASM_EXTABLE_HANDLE(from, to, ex_handler_fault)
 
@@ -165,8 +168,8 @@
 	jmp copy_user_handle_tail
 	.previous
 
-	_ASM_EXTABLE(100b,103b)
-	_ASM_EXTABLE(101b,103b)
+	_ASM_EXTABLE_UA(100b,103b)
+	_ASM_EXTABLE_UA(101b,103b)
 	.endm
 
 #else
@@ -182,6 +185,9 @@
 # define _ASM_EXTABLE(from, to)					\
 	_ASM_EXTABLE_HANDLE(from, to, ex_handler_default)
 
+# define _ASM_EXTABLE_UA(from, to)				\
+	_ASM_EXTABLE_HANDLE(from, to, ex_handler_uaccess)
+
 # define _ASM_EXTABLE_FAULT(from, to)				\
 	_ASM_EXTABLE_HANDLE(from, to, ex_handler_fault)
 
diff --git a/arch/x86/include/asm/extable.h b/arch/x86/include/asm/extable.h
index f9c3a5d502f4..93c1d28f3c73 100644
--- a/arch/x86/include/asm/extable.h
+++ b/arch/x86/include/asm/extable.h
@@ -29,7 +29,8 @@ struct pt_regs;
 		(b)->handler = (tmp).handler - (delta);		\
 	} while (0)
 
-extern int fixup_exception(struct pt_regs *regs, int trapnr);
+extern int fixup_exception(struct pt_regs *regs, int trapnr,
+			   unsigned long pf_addr);
 extern int fixup_bug(struct pt_regs *regs, int trapnr);
 extern bool ex_has_fault_handler(unsigned long ip);
 extern void early_fixup_exception(struct pt_regs *regs, int trapnr);
diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index a38bf5a1e37a..640e7721138c 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -113,7 +113,7 @@ extern void fpstate_sanitize_xstate(struct fpu *fpu);
 		     "3:  movl $-1,%[err]\n"				\
 		     "    jmp  2b\n"					\
 		     ".previous\n"					\
-		     _ASM_EXTABLE(1b, 3b)				\
+		     _ASM_EXTABLE_UA(1b, 3b)				\
 		     : [err] "=r" (err), output				\
 		     : "0"(0), input);					\
 	err;								\
@@ -226,7 +226,7 @@ static inline void copy_fxregs_to_kernel(struct fpu *fpu)
 		     "3: movl $-2,%[err]\n\t"				\
 		     "jmp 2b\n\t"					\
 		     ".popsection\n\t"					\
-		     _ASM_EXTABLE(1b, 3b)				\
+		     _ASM_EXTABLE_UA(1b, 3b)				\
 		     : [err] "=r" (err)					\
 		     : "D" (st), "m" (*st), "a" (lmask), "d" (hmask)	\
 		     : "memory")
@@ -256,7 +256,7 @@ static inline void copy_fxregs_to_kernel(struct fpu *fpu)
 		     "4: movl $-2, %[err]\n"				\
 		     "jmp 3b\n"						\
 		     ".popsection\n"					\
-		     _ASM_EXTABLE(661b, 4b)				\
+		     _ASM_EXTABLE_UA(661b, 4b)				\
 		     : [err] "=r" (err)					\
 		     : "D" (st), "m" (*st), "a" (lmask), "d" (hmask)	\
 		     : "memory")
diff --git a/arch/x86/include/asm/futex.h b/arch/x86/include/asm/futex.h
index de4d68852d3a..13c83fe97988 100644
--- a/arch/x86/include/asm/futex.h
+++ b/arch/x86/include/asm/futex.h
@@ -20,7 +20,7 @@
 		     "3:\tmov\t%3, %1\n"			\
 		     "\tjmp\t2b\n"				\
 		     "\t.previous\n"				\
-		     _ASM_EXTABLE(1b, 3b)			\
+		     _ASM_EXTABLE_UA(1b, 3b)			\
 		     : "=r" (oldval), "=r" (ret), "+m" (*uaddr)	\
 		     : "i" (-EFAULT), "0" (oparg), "1" (0))
 
@@ -36,8 +36,8 @@
 		     "4:\tmov\t%5, %1\n"			\
 		     "\tjmp\t3b\n"				\
 		     "\t.previous\n"				\
-		     _ASM_EXTABLE(1b, 4b)			\
-		     _ASM_EXTABLE(2b, 4b)			\
+		     _ASM_EXTABLE_UA(1b, 4b)			\
+		     _ASM_EXTABLE_UA(2b, 4b)			\
 		     : "=&a" (oldval), "=&r" (ret),		\
 		       "+m" (*uaddr), "=&r" (tem)		\
 		     : "r" (oparg), "i" (-EFAULT), "1" (0))
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index aae77eb8491c..b5e58cc0c5e7 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -198,8 +198,8 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
 		     "4:	movl %3,%0\n"				\
 		     "	jmp 3b\n"					\
 		     ".previous\n"					\
-		     _ASM_EXTABLE(1b, 4b)				\
-		     _ASM_EXTABLE(2b, 4b)				\
+		     _ASM_EXTABLE_UA(1b, 4b)				\
+		     _ASM_EXTABLE_UA(2b, 4b)				\
 		     : "=r" (err)					\
 		     : "A" (x), "r" (addr), "i" (errret), "0" (err))
 
@@ -340,8 +340,8 @@ do {									\
 		     "	xorl %%edx,%%edx\n"				\
 		     "	jmp 3b\n"					\
 		     ".previous\n"					\
-		     _ASM_EXTABLE(1b, 4b)				\
-		     _ASM_EXTABLE(2b, 4b)				\
+		     _ASM_EXTABLE_UA(1b, 4b)				\
+		     _ASM_EXTABLE_UA(2b, 4b)				\
 		     : "=r" (retval), "=&A"(x)				\
 		     : "m" (__m(__ptr)), "m" __m(((u32 __user *)(__ptr)) + 1),	\
 		       "i" (errret), "0" (retval));			\
@@ -386,7 +386,7 @@ do {									\
 		     "	xor"itype" %"rtype"1,%"rtype"1\n"		\
 		     "	jmp 2b\n"					\
 		     ".previous\n"					\
-		     _ASM_EXTABLE(1b, 3b)				\
+		     _ASM_EXTABLE_UA(1b, 3b)				\
 		     : "=r" (err), ltype(x)				\
 		     : "m" (__m(addr)), "i" (errret), "0" (err))
 
@@ -398,7 +398,7 @@ do {									\
 		     "3:	mov %3,%0\n"				\
 		     "	jmp 2b\n"					\
 		     ".previous\n"					\
-		     _ASM_EXTABLE(1b, 3b)				\
+		     _ASM_EXTABLE_UA(1b, 3b)				\
 		     : "=r" (err), ltype(x)				\
 		     : "m" (__m(addr)), "i" (errret), "0" (err))
 
@@ -474,7 +474,7 @@ struct __large_struct { unsigned long buf[100]; };
 		     "3:	mov %3,%0\n"				\
 		     "	jmp 2b\n"					\
 		     ".previous\n"					\
-		     _ASM_EXTABLE(1b, 3b)				\
+		     _ASM_EXTABLE_UA(1b, 3b)				\
 		     : "=r"(err)					\
 		     : ltype(x), "m" (__m(addr)), "i" (errret), "0" (err))
 
@@ -602,7 +602,7 @@ extern void __cmpxchg_wrong_size(void)
 			"3:\tmov     %3, %0\n"				\
 			"\tjmp     2b\n"				\
 			"\t.previous\n"					\
-			_ASM_EXTABLE(1b, 3b)				\
+			_ASM_EXTABLE_UA(1b, 3b)				\
 			: "+r" (__ret), "=a" (__old), "+m" (*(ptr))	\
 			: "i" (-EFAULT), "q" (__new), "1" (__old)	\
 			: "memory"					\
@@ -618,7 +618,7 @@ extern void __cmpxchg_wrong_size(void)
 			"3:\tmov     %3, %0\n"				\
 			"\tjmp     2b\n"				\
 			"\t.previous\n"					\
-			_ASM_EXTABLE(1b, 3b)				\
+			_ASM_EXTABLE_UA(1b, 3b)				\
 			: "+r" (__ret), "=a" (__old), "+m" (*(ptr))	\
 			: "i" (-EFAULT), "r" (__new), "1" (__old)	\
 			: "memory"					\
@@ -634,7 +634,7 @@ extern void __cmpxchg_wrong_size(void)
 			"3:\tmov     %3, %0\n"				\
 			"\tjmp     2b\n"				\
 			"\t.previous\n"					\
-			_ASM_EXTABLE(1b, 3b)				\
+			_ASM_EXTABLE_UA(1b, 3b)				\
 			: "+r" (__ret), "=a" (__old), "+m" (*(ptr))	\
 			: "i" (-EFAULT), "r" (__new), "1" (__old)	\
 			: "memory"					\
@@ -653,7 +653,7 @@ extern void __cmpxchg_wrong_size(void)
 			"3:\tmov     %3, %0\n"				\
 			"\tjmp     2b\n"				\
 			"\t.previous\n"					\
-			_ASM_EXTABLE(1b, 3b)				\
+			_ASM_EXTABLE_UA(1b, 3b)				\
 			: "+r" (__ret), "=a" (__old), "+m" (*(ptr))	\
 			: "i" (-EFAULT), "r" (__new), "1" (__old)	\
 			: "memory"					\
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 8c50754c09c1..e038e3f31e08 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -1335,7 +1335,7 @@ void do_machine_check(struct pt_regs *regs, long error_code)
 		local_irq_disable();
 		ist_end_non_atomic();
 	} else {
-		if (!fixup_exception(regs, X86_TRAP_MC))
+		if (!fixup_exception(regs, X86_TRAP_MC, 0))
 			mce_panic("Failed kernel mode recovery", &m, NULL);
 	}
 
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 6f4d42377fe5..5ad2639d3b8a 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -1044,7 +1044,7 @@ int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 		 * In case the user-specified fault handler returned
 		 * zero, try to fix up.
 		 */
-		if (fixup_exception(regs, trapnr))
+		if (fixup_exception(regs, trapnr, 0))
 			return 1;
 
 		/*
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index e6db475164ed..0cd11b46072a 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -206,7 +206,7 @@ do_trap_no_signal(struct task_struct *tsk, int trapnr, char *str,
 	}
 
 	if (!user_mode(regs)) {
-		if (fixup_exception(regs, trapnr))
+		if (fixup_exception(regs, trapnr, 0))
 			return 0;
 
 		tsk->thread.error_code = error_code;
@@ -551,7 +551,7 @@ do_general_protection(struct pt_regs *regs, long error_code)
 
 	tsk = current;
 	if (!user_mode(regs)) {
-		if (fixup_exception(regs, X86_TRAP_GP))
+		if (fixup_exception(regs, X86_TRAP_GP, 0))
 			return;
 
 		tsk->thread.error_code = error_code;
@@ -838,7 +838,7 @@ static void math_error(struct pt_regs *regs, int error_code, int trapnr)
 	cond_local_irq_enable(regs);
 
 	if (!user_mode(regs)) {
-		if (fixup_exception(regs, trapnr))
+		if (fixup_exception(regs, trapnr, 0))
 			return;
 
 		task->thread.error_code = error_code;
diff --git a/arch/x86/lib/checksum_32.S b/arch/x86/lib/checksum_32.S
index 46e71a74e612..ad8e0906d1ea 100644
--- a/arch/x86/lib/checksum_32.S
+++ b/arch/x86/lib/checksum_32.S
@@ -273,11 +273,11 @@ unsigned int csum_partial_copy_generic (const char *src, char *dst,
 
 #define SRC(y...)			\
 	9999: y;			\
-	_ASM_EXTABLE(9999b, 6001f)
+	_ASM_EXTABLE_UA(9999b, 6001f)
 
 #define DST(y...)			\
 	9999: y;			\
-	_ASM_EXTABLE(9999b, 6002f)
+	_ASM_EXTABLE_UA(9999b, 6002f)
 
 #ifndef CONFIG_X86_USE_PPRO_CHECKSUM
 
diff --git a/arch/x86/lib/copy_user_64.S b/arch/x86/lib/copy_user_64.S
index 020f75cc8cf6..80cfad666210 100644
--- a/arch/x86/lib/copy_user_64.S
+++ b/arch/x86/lib/copy_user_64.S
@@ -92,26 +92,26 @@ ENTRY(copy_user_generic_unrolled)
 60:	jmp copy_user_handle_tail /* ecx is zerorest also */
 	.previous
 
-	_ASM_EXTABLE(1b,30b)
-	_ASM_EXTABLE(2b,30b)
-	_ASM_EXTABLE(3b,30b)
-	_ASM_EXTABLE(4b,30b)
-	_ASM_EXTABLE(5b,30b)
-	_ASM_EXTABLE(6b,30b)
-	_ASM_EXTABLE(7b,30b)
-	_ASM_EXTABLE(8b,30b)
-	_ASM_EXTABLE(9b,30b)
-	_ASM_EXTABLE(10b,30b)
-	_ASM_EXTABLE(11b,30b)
-	_ASM_EXTABLE(12b,30b)
-	_ASM_EXTABLE(13b,30b)
-	_ASM_EXTABLE(14b,30b)
-	_ASM_EXTABLE(15b,30b)
-	_ASM_EXTABLE(16b,30b)
-	_ASM_EXTABLE(18b,40b)
-	_ASM_EXTABLE(19b,40b)
-	_ASM_EXTABLE(21b,50b)
-	_ASM_EXTABLE(22b,50b)
+	_ASM_EXTABLE_UA(1b,30b)
+	_ASM_EXTABLE_UA(2b,30b)
+	_ASM_EXTABLE_UA(3b,30b)
+	_ASM_EXTABLE_UA(4b,30b)
+	_ASM_EXTABLE_UA(5b,30b)
+	_ASM_EXTABLE_UA(6b,30b)
+	_ASM_EXTABLE_UA(7b,30b)
+	_ASM_EXTABLE_UA(8b,30b)
+	_ASM_EXTABLE_UA(9b,30b)
+	_ASM_EXTABLE_UA(10b,30b)
+	_ASM_EXTABLE_UA(11b,30b)
+	_ASM_EXTABLE_UA(12b,30b)
+	_ASM_EXTABLE_UA(13b,30b)
+	_ASM_EXTABLE_UA(14b,30b)
+	_ASM_EXTABLE_UA(15b,30b)
+	_ASM_EXTABLE_UA(16b,30b)
+	_ASM_EXTABLE_UA(18b,40b)
+	_ASM_EXTABLE_UA(19b,40b)
+	_ASM_EXTABLE_UA(21b,50b)
+	_ASM_EXTABLE_UA(22b,50b)
 ENDPROC(copy_user_generic_unrolled)
 EXPORT_SYMBOL(copy_user_generic_unrolled)
 
@@ -156,8 +156,8 @@ ENTRY(copy_user_generic_string)
 	jmp copy_user_handle_tail
 	.previous
 
-	_ASM_EXTABLE(1b,11b)
-	_ASM_EXTABLE(3b,12b)
+	_ASM_EXTABLE_UA(1b,11b)
+	_ASM_EXTABLE_UA(3b,12b)
 ENDPROC(copy_user_generic_string)
 EXPORT_SYMBOL(copy_user_generic_string)
 
@@ -189,7 +189,7 @@ ENTRY(copy_user_enhanced_fast_string)
 	jmp copy_user_handle_tail
 	.previous
 
-	_ASM_EXTABLE(1b,12b)
+	_ASM_EXTABLE_UA(1b,12b)
 ENDPROC(copy_user_enhanced_fast_string)
 EXPORT_SYMBOL(copy_user_enhanced_fast_string)
 
@@ -319,27 +319,27 @@ ENTRY(__copy_user_nocache)
 	jmp copy_user_handle_tail
 	.previous
 
-	_ASM_EXTABLE(1b,.L_fixup_4x8b_copy)
-	_ASM_EXTABLE(2b,.L_fixup_4x8b_copy)
-	_ASM_EXTABLE(3b,.L_fixup_4x8b_copy)
-	_ASM_EXTABLE(4b,.L_fixup_4x8b_copy)
-	_ASM_EXTABLE(5b,.L_fixup_4x8b_copy)
-	_ASM_EXTABLE(6b,.L_fixup_4x8b_copy)
-	_ASM_EXTABLE(7b,.L_fixup_4x8b_copy)
-	_ASM_EXTABLE(8b,.L_fixup_4x8b_copy)
-	_ASM_EXTABLE(9b,.L_fixup_4x8b_copy)
-	_ASM_EXTABLE(10b,.L_fixup_4x8b_copy)
-	_ASM_EXTABLE(11b,.L_fixup_4x8b_copy)
-	_ASM_EXTABLE(12b,.L_fixup_4x8b_copy)
-	_ASM_EXTABLE(13b,.L_fixup_4x8b_copy)
-	_ASM_EXTABLE(14b,.L_fixup_4x8b_copy)
-	_ASM_EXTABLE(15b,.L_fixup_4x8b_copy)
-	_ASM_EXTABLE(16b,.L_fixup_4x8b_copy)
-	_ASM_EXTABLE(20b,.L_fixup_8b_copy)
-	_ASM_EXTABLE(21b,.L_fixup_8b_copy)
-	_ASM_EXTABLE(30b,.L_fixup_4b_copy)
-	_ASM_EXTABLE(31b,.L_fixup_4b_copy)
-	_ASM_EXTABLE(40b,.L_fixup_1b_copy)
-	_ASM_EXTABLE(41b,.L_fixup_1b_copy)
+	_ASM_EXTABLE_UA(1b,.L_fixup_4x8b_copy)
+	_ASM_EXTABLE_UA(2b,.L_fixup_4x8b_copy)
+	_ASM_EXTABLE_UA(3b,.L_fixup_4x8b_copy)
+	_ASM_EXTABLE_UA(4b,.L_fixup_4x8b_copy)
+	_ASM_EXTABLE_UA(5b,.L_fixup_4x8b_copy)
+	_ASM_EXTABLE_UA(6b,.L_fixup_4x8b_copy)
+	_ASM_EXTABLE_UA(7b,.L_fixup_4x8b_copy)
+	_ASM_EXTABLE_UA(8b,.L_fixup_4x8b_copy)
+	_ASM_EXTABLE_UA(9b,.L_fixup_4x8b_copy)
+	_ASM_EXTABLE_UA(10b,.L_fixup_4x8b_copy)
+	_ASM_EXTABLE_UA(11b,.L_fixup_4x8b_copy)
+	_ASM_EXTABLE_UA(12b,.L_fixup_4x8b_copy)
+	_ASM_EXTABLE_UA(13b,.L_fixup_4x8b_copy)
+	_ASM_EXTABLE_UA(14b,.L_fixup_4x8b_copy)
+	_ASM_EXTABLE_UA(15b,.L_fixup_4x8b_copy)
+	_ASM_EXTABLE_UA(16b,.L_fixup_4x8b_copy)
+	_ASM_EXTABLE_UA(20b,.L_fixup_8b_copy)
+	_ASM_EXTABLE_UA(21b,.L_fixup_8b_copy)
+	_ASM_EXTABLE_UA(30b,.L_fixup_4b_copy)
+	_ASM_EXTABLE_UA(31b,.L_fixup_4b_copy)
+	_ASM_EXTABLE_UA(40b,.L_fixup_1b_copy)
+	_ASM_EXTABLE_UA(41b,.L_fixup_1b_copy)
 ENDPROC(__copy_user_nocache)
 EXPORT_SYMBOL(__copy_user_nocache)
diff --git a/arch/x86/lib/csum-copy_64.S b/arch/x86/lib/csum-copy_64.S
index 45a53dfe1859..969af904c74b 100644
--- a/arch/x86/lib/csum-copy_64.S
+++ b/arch/x86/lib/csum-copy_64.S
@@ -31,17 +31,17 @@
 
 	.macro source
 10:
-	_ASM_EXTABLE(10b, .Lbad_source)
+	_ASM_EXTABLE_UA(10b, .Lbad_source)
 	.endm
 
 	.macro dest
 20:
-	_ASM_EXTABLE(20b, .Lbad_dest)
+	_ASM_EXTABLE_UA(20b, .Lbad_dest)
 	.endm
 
 	.macro ignore L=.Lignore
 30:
-	_ASM_EXTABLE(30b, \L)
+	_ASM_EXTABLE_UA(30b, \L)
 	.endm
 
 
diff --git a/arch/x86/lib/getuser.S b/arch/x86/lib/getuser.S
index 49b167f73215..884fe795d9d6 100644
--- a/arch/x86/lib/getuser.S
+++ b/arch/x86/lib/getuser.S
@@ -132,12 +132,12 @@ bad_get_user_8:
 END(bad_get_user_8)
 #endif
 
-	_ASM_EXTABLE(1b,bad_get_user)
-	_ASM_EXTABLE(2b,bad_get_user)
-	_ASM_EXTABLE(3b,bad_get_user)
+	_ASM_EXTABLE_UA(1b,bad_get_user)
+	_ASM_EXTABLE_UA(2b,bad_get_user)
+	_ASM_EXTABLE_UA(3b,bad_get_user)
 #ifdef CONFIG_X86_64
-	_ASM_EXTABLE(4b,bad_get_user)
+	_ASM_EXTABLE_UA(4b,bad_get_user)
 #else
-	_ASM_EXTABLE(4b,bad_get_user_8)
-	_ASM_EXTABLE(5b,bad_get_user_8)
+	_ASM_EXTABLE_UA(4b,bad_get_user_8)
+	_ASM_EXTABLE_UA(5b,bad_get_user_8)
 #endif
diff --git a/arch/x86/lib/putuser.S b/arch/x86/lib/putuser.S
index 96dce5fe2a35..cdcf6143d953 100644
--- a/arch/x86/lib/putuser.S
+++ b/arch/x86/lib/putuser.S
@@ -94,10 +94,10 @@ bad_put_user:
 	EXIT
 END(bad_put_user)
 
-	_ASM_EXTABLE(1b,bad_put_user)
-	_ASM_EXTABLE(2b,bad_put_user)
-	_ASM_EXTABLE(3b,bad_put_user)
-	_ASM_EXTABLE(4b,bad_put_user)
+	_ASM_EXTABLE_UA(1b,bad_put_user)
+	_ASM_EXTABLE_UA(2b,bad_put_user)
+	_ASM_EXTABLE_UA(3b,bad_put_user)
+	_ASM_EXTABLE_UA(4b,bad_put_user)
 #ifdef CONFIG_X86_32
-	_ASM_EXTABLE(5b,bad_put_user)
+	_ASM_EXTABLE_UA(5b,bad_put_user)
 #endif
diff --git a/arch/x86/lib/usercopy_32.c b/arch/x86/lib/usercopy_32.c
index 7add8ba06887..92eb5956f2f3 100644
--- a/arch/x86/lib/usercopy_32.c
+++ b/arch/x86/lib/usercopy_32.c
@@ -47,8 +47,8 @@ do {									\
 		"3:	lea 0(%2,%0,4),%0\n"				\
 		"	jmp 2b\n"					\
 		".previous\n"						\
-		_ASM_EXTABLE(0b,3b)					\
-		_ASM_EXTABLE(1b,2b)					\
+		_ASM_EXTABLE_UA(0b,3b)					\
+		_ASM_EXTABLE_UA(1b,2b)					\
 		: "=&c"(size), "=&D" (__d0)				\
 		: "r"(size & 3), "0"(size / 4), "1"(addr), "a"(0));	\
 } while (0)
@@ -153,44 +153,44 @@ __copy_user_intel(void __user *to, const void *from, unsigned long size)
 		       "101:   lea 0(%%eax,%0,4),%0\n"
 		       "       jmp 100b\n"
 		       ".previous\n"
-		       _ASM_EXTABLE(1b,100b)
-		       _ASM_EXTABLE(2b,100b)
-		       _ASM_EXTABLE(3b,100b)
-		       _ASM_EXTABLE(4b,100b)
-		       _ASM_EXTABLE(5b,100b)
-		       _ASM_EXTABLE(6b,100b)
-		       _ASM_EXTABLE(7b,100b)
-		       _ASM_EXTABLE(8b,100b)
-		       _ASM_EXTABLE(9b,100b)
-		       _ASM_EXTABLE(10b,100b)
-		       _ASM_EXTABLE(11b,100b)
-		       _ASM_EXTABLE(12b,100b)
-		       _ASM_EXTABLE(13b,100b)
-		       _ASM_EXTABLE(14b,100b)
-		       _ASM_EXTABLE(15b,100b)
-		       _ASM_EXTABLE(16b,100b)
-		       _ASM_EXTABLE(17b,100b)
-		       _ASM_EXTABLE(18b,100b)
-		       _ASM_EXTABLE(19b,100b)
-		       _ASM_EXTABLE(20b,100b)
-		       _ASM_EXTABLE(21b,100b)
-		       _ASM_EXTABLE(22b,100b)
-		       _ASM_EXTABLE(23b,100b)
-		       _ASM_EXTABLE(24b,100b)
-		       _ASM_EXTABLE(25b,100b)
-		       _ASM_EXTABLE(26b,100b)
-		       _ASM_EXTABLE(27b,100b)
-		       _ASM_EXTABLE(28b,100b)
-		       _ASM_EXTABLE(29b,100b)
-		       _ASM_EXTABLE(30b,100b)
-		       _ASM_EXTABLE(31b,100b)
-		       _ASM_EXTABLE(32b,100b)
-		       _ASM_EXTABLE(33b,100b)
-		       _ASM_EXTABLE(34b,100b)
-		       _ASM_EXTABLE(35b,100b)
-		       _ASM_EXTABLE(36b,100b)
-		       _ASM_EXTABLE(37b,100b)
-		       _ASM_EXTABLE(99b,101b)
+		       _ASM_EXTABLE_UA(1b,100b)
+		       _ASM_EXTABLE_UA(2b,100b)
+		       _ASM_EXTABLE_UA(3b,100b)
+		       _ASM_EXTABLE_UA(4b,100b)
+		       _ASM_EXTABLE_UA(5b,100b)
+		       _ASM_EXTABLE_UA(6b,100b)
+		       _ASM_EXTABLE_UA(7b,100b)
+		       _ASM_EXTABLE_UA(8b,100b)
+		       _ASM_EXTABLE_UA(9b,100b)
+		       _ASM_EXTABLE_UA(10b,100b)
+		       _ASM_EXTABLE_UA(11b,100b)
+		       _ASM_EXTABLE_UA(12b,100b)
+		       _ASM_EXTABLE_UA(13b,100b)
+		       _ASM_EXTABLE_UA(14b,100b)
+		       _ASM_EXTABLE_UA(15b,100b)
+		       _ASM_EXTABLE_UA(16b,100b)
+		       _ASM_EXTABLE_UA(17b,100b)
+		       _ASM_EXTABLE_UA(18b,100b)
+		       _ASM_EXTABLE_UA(19b,100b)
+		       _ASM_EXTABLE_UA(20b,100b)
+		       _ASM_EXTABLE_UA(21b,100b)
+		       _ASM_EXTABLE_UA(22b,100b)
+		       _ASM_EXTABLE_UA(23b,100b)
+		       _ASM_EXTABLE_UA(24b,100b)
+		       _ASM_EXTABLE_UA(25b,100b)
+		       _ASM_EXTABLE_UA(26b,100b)
+		       _ASM_EXTABLE_UA(27b,100b)
+		       _ASM_EXTABLE_UA(28b,100b)
+		       _ASM_EXTABLE_UA(29b,100b)
+		       _ASM_EXTABLE_UA(30b,100b)
+		       _ASM_EXTABLE_UA(31b,100b)
+		       _ASM_EXTABLE_UA(32b,100b)
+		       _ASM_EXTABLE_UA(33b,100b)
+		       _ASM_EXTABLE_UA(34b,100b)
+		       _ASM_EXTABLE_UA(35b,100b)
+		       _ASM_EXTABLE_UA(36b,100b)
+		       _ASM_EXTABLE_UA(37b,100b)
+		       _ASM_EXTABLE_UA(99b,101b)
 		       : "=&c"(size), "=&D" (d0), "=&S" (d1)
 		       :  "1"(to), "2"(from), "0"(size)
 		       : "eax", "edx", "memory");
@@ -259,26 +259,26 @@ static unsigned long __copy_user_intel_nocache(void *to,
 	       "9:      lea 0(%%eax,%0,4),%0\n"
 	       "16:     jmp 8b\n"
 	       ".previous\n"
-	       _ASM_EXTABLE(0b,16b)
-	       _ASM_EXTABLE(1b,16b)
-	       _ASM_EXTABLE(2b,16b)
-	       _ASM_EXTABLE(21b,16b)
-	       _ASM_EXTABLE(3b,16b)
-	       _ASM_EXTABLE(31b,16b)
-	       _ASM_EXTABLE(4b,16b)
-	       _ASM_EXTABLE(41b,16b)
-	       _ASM_EXTABLE(10b,16b)
-	       _ASM_EXTABLE(51b,16b)
-	       _ASM_EXTABLE(11b,16b)
-	       _ASM_EXTABLE(61b,16b)
-	       _ASM_EXTABLE(12b,16b)
-	       _ASM_EXTABLE(71b,16b)
-	       _ASM_EXTABLE(13b,16b)
-	       _ASM_EXTABLE(81b,16b)
-	       _ASM_EXTABLE(14b,16b)
-	       _ASM_EXTABLE(91b,16b)
-	       _ASM_EXTABLE(6b,9b)
-	       _ASM_EXTABLE(7b,16b)
+	       _ASM_EXTABLE_UA(0b,16b)
+	       _ASM_EXTABLE_UA(1b,16b)
+	       _ASM_EXTABLE_UA(2b,16b)
+	       _ASM_EXTABLE_UA(21b,16b)
+	       _ASM_EXTABLE_UA(3b,16b)
+	       _ASM_EXTABLE_UA(31b,16b)
+	       _ASM_EXTABLE_UA(4b,16b)
+	       _ASM_EXTABLE_UA(41b,16b)
+	       _ASM_EXTABLE_UA(10b,16b)
+	       _ASM_EXTABLE_UA(51b,16b)
+	       _ASM_EXTABLE_UA(11b,16b)
+	       _ASM_EXTABLE_UA(61b,16b)
+	       _ASM_EXTABLE_UA(12b,16b)
+	       _ASM_EXTABLE_UA(71b,16b)
+	       _ASM_EXTABLE_UA(13b,16b)
+	       _ASM_EXTABLE_UA(81b,16b)
+	       _ASM_EXTABLE_UA(14b,16b)
+	       _ASM_EXTABLE_UA(91b,16b)
+	       _ASM_EXTABLE_UA(6b,9b)
+	       _ASM_EXTABLE_UA(7b,16b)
 	       : "=&c"(size), "=&D" (d0), "=&S" (d1)
 	       :  "1"(to), "2"(from), "0"(size)
 	       : "eax", "edx", "memory");
@@ -321,9 +321,9 @@ do {									\
 		"3:	lea 0(%3,%0,4),%0\n"				\
 		"	jmp 2b\n"					\
 		".previous\n"						\
-		_ASM_EXTABLE(4b,5b)					\
-		_ASM_EXTABLE(0b,3b)					\
-		_ASM_EXTABLE(1b,2b)					\
+		_ASM_EXTABLE_UA(4b,5b)					\
+		_ASM_EXTABLE_UA(0b,3b)					\
+		_ASM_EXTABLE_UA(1b,2b)					\
 		: "=&c"(size), "=&D" (__d0), "=&S" (__d1), "=r"(__d2)	\
 		: "3"(size), "0"(size), "1"(to), "2"(from)		\
 		: "memory");						\
diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
index 9c5606d88f61..c55b1f590cc4 100644
--- a/arch/x86/lib/usercopy_64.c
+++ b/arch/x86/lib/usercopy_64.c
@@ -37,8 +37,8 @@ unsigned long __clear_user(void __user *addr, unsigned long size)
 		"3:	lea 0(%[size1],%[size8],8),%[size8]\n"
 		"	jmp 2b\n"
 		".previous\n"
-		_ASM_EXTABLE(0b,3b)
-		_ASM_EXTABLE(1b,2b)
+		_ASM_EXTABLE_UA(0b,3b)
+		_ASM_EXTABLE_UA(1b,2b)
 		: [size8] "=&c"(size), [dst] "=&D" (__d0)
 		: [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr));
 	clac();
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 45f5d6cf65ae..3fd55a03892d 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -8,7 +8,7 @@
 #include <asm/kdebug.h>
 
 typedef bool (*ex_handler_t)(const struct exception_table_entry *,
-			    struct pt_regs *, int);
+			    struct pt_regs *, int, unsigned long);
 
 static inline unsigned long
 ex_fixup_addr(const struct exception_table_entry *x)
@@ -22,7 +22,8 @@ ex_fixup_handler(const struct exception_table_entry *x)
 }
 
 __visible bool ex_handler_default(const struct exception_table_entry *fixup,
-				  struct pt_regs *regs, int trapnr)
+				  struct pt_regs *regs, int trapnr,
+				  unsigned long fault_addr)
 {
 	regs->ip = ex_fixup_addr(fixup);
 	return true;
@@ -30,7 +31,8 @@ __visible bool ex_handler_default(const struct exception_table_entry *fixup,
 EXPORT_SYMBOL(ex_handler_default);
 
 __visible bool ex_handler_fault(const struct exception_table_entry *fixup,
-				struct pt_regs *regs, int trapnr)
+				struct pt_regs *regs, int trapnr,
+				unsigned long fault_addr)
 {
 	regs->ip = ex_fixup_addr(fixup);
 	regs->ax = trapnr;
@@ -43,7 +45,8 @@ EXPORT_SYMBOL_GPL(ex_handler_fault);
  * result of a refcount inc/dec/add/sub.
  */
 __visible bool ex_handler_refcount(const struct exception_table_entry *fixup,
-				   struct pt_regs *regs, int trapnr)
+				   struct pt_regs *regs, int trapnr,
+				   unsigned long fault_addr)
 {
 	/* First unconditionally saturate the refcount. */
 	*(int *)regs->cx = INT_MIN / 2;
@@ -96,7 +99,8 @@ EXPORT_SYMBOL(ex_handler_refcount);
  * out all the FPU registers) if we can't restore from the task's FPU state.
  */
 __visible bool ex_handler_fprestore(const struct exception_table_entry *fixup,
-				    struct pt_regs *regs, int trapnr)
+				    struct pt_regs *regs, int trapnr,
+				    unsigned long fault_addr)
 {
 	regs->ip = ex_fixup_addr(fixup);
 
@@ -108,18 +112,53 @@ __visible bool ex_handler_fprestore(const struct exception_table_entry *fixup,
 }
 EXPORT_SYMBOL_GPL(ex_handler_fprestore);
 
+static void bogus_uaccess_check(struct pt_regs *regs, int trapnr,
+				unsigned long fault_addr)
+{
+	if (trapnr != X86_TRAP_PF || fault_addr < TASK_SIZE_MAX)
+		return;
+	/*
+	 * This is a pagefault in kernel space, on a kernel address, in a
+	 * usercopy function. This can e.g. be caused by improper use of helpers
+	 * like __put_user and by improper attempts to access userspace
+	 * addresses in KERNEL_DS regions. The one legitimate exception are
+	 * probe_kernel_{read,write}(), which can be invoked from places like
+	 * kgdb, /dev/mem (for reading) and privileged BPF code (for reading).
+	 * The probe_kernel_*() functions set the kernel_uaccess_faults_ok flag
+	 * to tell us that faulting on kernel addresses in a userspace accessor
+	 * is fine.
+	 */
+	if (current->kernel_uaccess_faults_ok)
+		return;
+	WARN(1, "pagefault on kernel address 0x%lx in non-whitelisted uaccess",
+	     fault_addr);
+}
+
+__visible bool ex_handler_uaccess(const struct exception_table_entry *fixup,
+				  struct pt_regs *regs, int trapnr,
+				  unsigned long fault_addr)
+{
+	bogus_uaccess_check(regs, trapnr, fault_addr);
+	regs->ip = ex_fixup_addr(fixup);
+	return true;
+}
+EXPORT_SYMBOL(ex_handler_uaccess);
+
 __visible bool ex_handler_ext(const struct exception_table_entry *fixup,
-			      struct pt_regs *regs, int trapnr)
+			      struct pt_regs *regs, int trapnr,
+			      unsigned long fault_addr)
 {
 	/* Special hack for uaccess_err */
 	current->thread.uaccess_err = 1;
+	bogus_uaccess_check(regs, trapnr, fault_addr);
 	regs->ip = ex_fixup_addr(fixup);
 	return true;
 }
 EXPORT_SYMBOL(ex_handler_ext);
 
 __visible bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup,
-				       struct pt_regs *regs, int trapnr)
+				       struct pt_regs *regs, int trapnr,
+				       unsigned long fault_addr)
 {
 	if (pr_warn_once("unchecked MSR access error: RDMSR from 0x%x at rIP: 0x%lx (%pF)\n",
 			 (unsigned int)regs->cx, regs->ip, (void *)regs->ip))
@@ -134,7 +173,8 @@ __visible bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup
 EXPORT_SYMBOL(ex_handler_rdmsr_unsafe);
 
 __visible bool ex_handler_wrmsr_unsafe(const struct exception_table_entry *fixup,
-				       struct pt_regs *regs, int trapnr)
+				       struct pt_regs *regs, int trapnr,
+				       unsigned long fault_addr)
 {
 	if (pr_warn_once("unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x) at rIP: 0x%lx (%pF)\n",
 			 (unsigned int)regs->cx, (unsigned int)regs->dx,
@@ -148,12 +188,13 @@ __visible bool ex_handler_wrmsr_unsafe(const struct exception_table_entry *fixup
 EXPORT_SYMBOL(ex_handler_wrmsr_unsafe);
 
 __visible bool ex_handler_clear_fs(const struct exception_table_entry *fixup,
-				   struct pt_regs *regs, int trapnr)
+				   struct pt_regs *regs, int trapnr,
+				   unsigned long fault_addr)
 {
 	if (static_cpu_has(X86_BUG_NULL_SEG))
 		asm volatile ("mov %0, %%fs" : : "rm" (__USER_DS));
 	asm volatile ("mov %0, %%fs" : : "rm" (0));
-	return ex_handler_default(fixup, regs, trapnr);
+	return ex_handler_default(fixup, regs, trapnr, fault_addr);
 }
 EXPORT_SYMBOL(ex_handler_clear_fs);
 
@@ -170,7 +211,7 @@ __visible bool ex_has_fault_handler(unsigned long ip)
 	return handler == ex_handler_fault;
 }
 
-int fixup_exception(struct pt_regs *regs, int trapnr)
+int fixup_exception(struct pt_regs *regs, int trapnr, unsigned long fault_addr)
 {
 	const struct exception_table_entry *e;
 	ex_handler_t handler;
@@ -194,7 +235,7 @@ int fixup_exception(struct pt_regs *regs, int trapnr)
 		return 0;
 
 	handler = ex_fixup_handler(e);
-	return handler(e, regs, trapnr);
+	return handler(e, regs, trapnr, fault_addr);
 }
 
 extern unsigned int early_recursion_flag;
@@ -232,7 +273,7 @@ void __init early_fixup_exception(struct pt_regs *regs, int trapnr)
 	 * Keep in mind that not all vectors actually get here.  Early
 	 * fage faults, for example, are special.
 	 */
-	if (fixup_exception(regs, trapnr))
+	if (fixup_exception(regs, trapnr, 0))
 		return;
 
 	if (fixup_bug(regs, trapnr))
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 2aafa6ab6103..96e3e5cf2cfc 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -710,7 +710,7 @@ no_context(struct pt_regs *regs, unsigned long error_code,
 	int sig;
 
 	/* Are we prepared to handle this kernel fault? */
-	if (fixup_exception(regs, X86_TRAP_PF)) {
+	if (fixup_exception(regs, X86_TRAP_PF, address)) {
 		/*
 		 * Any interrupt that takes a fault gets the fixup. This makes
 		 * the below recursive fault logic only apply to a faults from
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 43731fe51c97..b50598761ed4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -734,6 +734,8 @@ struct task_struct {
 	/* disallow userland-initiated cgroup migration */
 	unsigned			no_cgroup_migration:1;
 #endif
+	/* usercopy functions may fault on kernel addresses */
+	unsigned int			kernel_uaccess_faults_ok:1;
 
 	unsigned long			atomic_flags; /* Flags requiring atomic access. */
 
diff --git a/mm/maccess.c b/mm/maccess.c
index ec00be51a24f..e066aa8482af 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -30,8 +30,10 @@ long __probe_kernel_read(void *dst, const void *src, size_t size)
 
 	set_fs(KERNEL_DS);
 	pagefault_disable();
+	current->kernel_uaccess_faults_ok = 1;
 	ret = __copy_from_user_inatomic(dst,
 			(__force const void __user *)src, size);
+	current->kernel_uaccess_faults_ok = 0;
 	pagefault_enable();
 	set_fs(old_fs);
 
@@ -58,7 +60,9 @@ long __probe_kernel_write(void *dst, const void *src, size_t size)
 
 	set_fs(KERNEL_DS);
 	pagefault_disable();
+	current->kernel_uaccess_faults_ok = 1;
 	ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
+	current->kernel_uaccess_faults_ok = 0;
 	pagefault_enable();
 	set_fs(old_fs);
 
@@ -94,11 +98,13 @@ long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)
 
 	set_fs(KERNEL_DS);
 	pagefault_disable();
+	current->kernel_uaccess_faults_ok = 1;
 
 	do {
 		ret = __get_user(*dst++, (const char __user __force *)src++);
 	} while (dst[-1] && ret == 0 && src - unsafe_addr < count);
 
+	current->kernel_uaccess_faults_ok = 0;
 	dst[-1] = '\0';
 	pagefault_enable();
 	set_fs(old_fs);
-- 
2.18.0.597.ga71716f1ad-goog

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