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Subject[PATCH 3/3] x86: add failure injection to get/put/clear_user
Date
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
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