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From:   albert.linde@gmail.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 van der Linde <alinde@google.com>
Subject: [PATCH 3/3] x86: add failure injection to get/put/clear_user
Date:   Fri, 21 Aug 2020 10:49:25 +0000
Message-Id: <20200821104926.828511-4-alinde@google.com>
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From: Albert van der Linde <alinde@google.com>

To test fault-tolerance of usercopy accesses in x86, add support for
fault injection.

Make both put_user() and get_user() fail with -EFAULT, and clear_user()
fail by partially clearing fewer bytes.

Signed-off-by: Albert van der Linde <alinde@google.com>
---
 arch/x86/include/asm/uaccess.h | 70 +++++++++++++++++++---------------
 arch/x86/lib/usercopy_64.c     |  9 ++++-
 2 files changed, 48 insertions(+), 31 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index ecefaffd15d4..dacb6105831e 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>
@@ -174,12 +175,17 @@ extern int __get_user_bad(void);
 	int __ret_gu;							\
 	register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX);		\
 	__chk_user_ptr(ptr);						\
-	might_fault();							\
-	asm volatile("call __get_user_%P4"				\
-		     : "=a" (__ret_gu), "=r" (__val_gu),		\
+	if (should_fail_usercopy(sizeof(*(ptr)))) {			\
+		(x) = 0;						\
+		__ret_gu = -EFAULT;					\
+	} else {							\
+		might_fault();						\
+		asm volatile("call __get_user_%P4"			\
+			: "=a" (__ret_gu), "=r" (__val_gu),		\
 			ASM_CALL_CONSTRAINT				\
-		     : "0" (ptr), "i" (sizeof(*(ptr))));		\
-	(x) = (__force __typeof__(*(ptr))) __val_gu;			\
+			: "0" (ptr), "i" (sizeof(*(ptr))));		\
+		(x) = (__force __typeof__(*(ptr))) __val_gu;		\
+	}								\
 	__builtin_expect(__ret_gu, 0);					\
 })
 
@@ -236,31 +242,35 @@ extern void __put_user_8(void);
  *
  * Return: zero on success, or -EFAULT on error.
  */
-#define put_user(x, ptr)					\
-({								\
-	int __ret_pu;						\
-	__typeof__(*(ptr)) __pu_val;				\
-	__chk_user_ptr(ptr);					\
-	might_fault();						\
-	__pu_val = x;						\
-	switch (sizeof(*(ptr))) {				\
-	case 1:							\
-		__put_user_x(1, __pu_val, ptr, __ret_pu);	\
-		break;						\
-	case 2:							\
-		__put_user_x(2, __pu_val, ptr, __ret_pu);	\
-		break;						\
-	case 4:							\
-		__put_user_x(4, __pu_val, ptr, __ret_pu);	\
-		break;						\
-	case 8:							\
-		__put_user_x8(__pu_val, ptr, __ret_pu);		\
-		break;						\
-	default:						\
-		__put_user_x(X, __pu_val, ptr, __ret_pu);	\
-		break;						\
-	}							\
-	__builtin_expect(__ret_pu, 0);				\
+#define put_user(x, ptr)						\
+({									\
+	int __ret_pu;							\
+	__typeof__(*(ptr)) __pu_val;					\
+	__chk_user_ptr(ptr);						\
+	might_fault();							\
+	__pu_val = x;							\
+	if (should_fail_usercopy(sizeof(*(ptr)))) {			\
+		__ret_pu = -EFAULT;					\
+	} else {							\
+		switch (sizeof(*(ptr))) {				\
+		case 1:							\
+			__put_user_x(1, __pu_val, ptr, __ret_pu);	\
+			break;						\
+		case 2:							\
+			__put_user_x(2, __pu_val, ptr, __ret_pu);	\
+			break;						\
+		case 4:							\
+			__put_user_x(4, __pu_val, ptr, __ret_pu);	\
+			break;						\
+		case 8:							\
+			__put_user_x8(__pu_val, ptr, __ret_pu);		\
+			break;						\
+		default:						\
+			__put_user_x(X, __pu_val, ptr, __ret_pu);	\
+			break;						\
+		}							\
+	}								\
+	__builtin_expect(__ret_pu, 0);					\
 })
 
 #define __put_user_size(x, ptr, size, label)				\
diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
index b0dfac3d3df7..b749590d753e 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>
 
@@ -50,8 +51,14 @@ EXPORT_SYMBOL(__clear_user);
 
 unsigned long clear_user(void __user *to, unsigned long n)
 {
+	long not_copied = should_fail_usercopy(n);
+
+	if (not_copied < 0)
+		not_copied = n;
+
 	if (access_ok(to, n))
-		return __clear_user(to, n);
+		return not_copied + __clear_user(to, n - not_copied);
+
 	return n;
 }
 EXPORT_SYMBOL(clear_user);
-- 
2.28.0.297.g1956fa8f8d-goog