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Date:   Fri, 23 Oct 2020 10:16:28 +0200
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Subject: [PATCH v4] x86: add failure injection to get/put/clear_user
From:   Alexander Potapenko <glider@google.com>
To:     akpm@linux-foundation.org, bp@alien8.de, mingo@redhat.com,
        corbet@lwn.net, tglx@linutronix.de, arnd@arndb.de
Cc:     akinobu.mita@gmail.com, hpa@zytor.com, viro@zeniv.linux.org.uk,
        glider@google.com, andreyknvl@google.com, dvyukov@google.com,
        elver@google.com, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
        x86@kernel.org, albert.linde@gmail.com,
        Albert van der Linde <alinde@google.com>
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From: Albert van der Linde <alinde@google.com>

To test fault-tolerance of user memory acceses in x86, add support for
fault injection.

Make both put_user() and get_user() fail with -EFAULT, and clear_user()
fail by not clearing any bytes.

Reviewed-by: Akinobu Mita <akinobu.mita@gmail.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Albert van der Linde <alinde@google.com>
Signed-off-by: Alexander Potapenko <glider@google.com>

---
v2:
 - no significant changes

v3:
 - no changes

v4:
 - instrument the new out-of-line implementations of get_user()/put_user()
 - fix a minor checkpatch warning in the inline assembly

---
---
 arch/x86/include/asm/uaccess.h | 36 ++++++++++++++++++++++------------
 arch/x86/lib/usercopy_64.c     |  3 +++
 2 files changed, 26 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index f13659523108..7041ebc48b75 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -5,6 +5,7 @@
  * User space memory access functions
  */
 #include <linux/compiler.h>
+#include <linux/fault-inject-usercopy.h>
 #include <linux/kasan-checks.h>
 #include <linux/string.h>
 #include <asm/asm.h>
@@ -126,11 +127,16 @@ 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 "_%P4"				\
-		     : "=a" (__ret_gu), "=r" (__val_gu),		\
-			ASM_CALL_CONSTRAINT				\
-		     : "0" (ptr), "i" (sizeof(*(ptr))));		\
-	(x) = (__force __typeof__(*(ptr))) __val_gu;			\
+	if (should_fail_usercopy()) {					\
+		(x) = 0;						\
+		__ret_gu = -EFAULT;					\
+	} else {							\
+		asm volatile("call __" #fn "_%P4"			\
+			     : "=a" (__ret_gu), "=r" (__val_gu),	\
+				ASM_CALL_CONSTRAINT			\
+			     : "0" (ptr), "i" (sizeof(*(ptr))));	\
+		(x) = (__force __typeof__(*(ptr))) __val_gu;		\
+	}								\
 	__builtin_expect(__ret_gu, 0);					\
 })
 
@@ -213,14 +219,18 @@ extern void __put_user_nocheck_8(void);
 	int __ret_pu;							\
 	register __typeof__(*(ptr)) __val_pu asm("%"_ASM_AX);		\
 	__chk_user_ptr(ptr);						\
-	__val_pu = (x);							\
-	asm volatile("call __" #fn "_%P[size]"				\
-		     : "=c" (__ret_pu),					\
-			ASM_CALL_CONSTRAINT				\
-		     : "0" (ptr),					\
-		       "r" (__val_pu),					\
-		       [size] "i" (sizeof(*(ptr)))			\
-		     :"ebx");						\
+	if (unlikely(should_fail_usercopy())) {				\
+		__ret_pu = -EFAULT;					\
+	} else {							\
+		__val_pu = (x);						\
+		asm volatile("call __" #fn "_%P[size]"			\
+			     : "=c" (__ret_pu),				\
+				ASM_CALL_CONSTRAINT			\
+			     : "0" (ptr),				\
+			       "r" (__val_pu),				\
+			       [size] "i" (sizeof(*(ptr)))		\
+			     : "ebx");					\
+	}								\
 	__builtin_expect(__ret_pu, 0);					\
 })
 
diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
index 508c81e97ab1..5617b3864586 100644
--- a/arch/x86/lib/usercopy_64.c
+++ b/arch/x86/lib/usercopy_64.c
@@ -7,6 +7,7 @@
  * Copyright 2002 Andi Kleen <ak@suse.de>
  */
 #include <linux/export.h>
+#include <linux/fault-inject-usercopy.h>
 #include <linux/uaccess.h>
 #include <linux/highmem.h>
 
@@ -50,6 +51,8 @@ EXPORT_SYMBOL(__clear_user);
 
 unsigned long clear_user(void __user *to, unsigned long n)
 {
+	if (should_fail_usercopy())
+		return n;
 	if (access_ok(to, n))
 		return __clear_user(to, n);
 	return n;
-- 
2.29.0.rc2.309.g374f81d7ae-goog