ARM: uaccess: provide uaccess_save_and_enable() and uaccess_restore()
Provide uaccess_save_and_enable() and uaccess_restore() to permit
control of userspace visibility to the kernel, and hook these into
the appropriate places in the kernel where we need to access
userspace.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index 74b17d0..8288013 100644
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -50,6 +50,21 @@
extern int fixup_exception(struct pt_regs *regs);
/*
+ * These two functions allow hooking accesses to userspace to increase
+ * system integrity by ensuring that the kernel can not inadvertantly
+ * perform such accesses (eg, via list poison values) which could then
+ * be exploited for priviledge escalation.
+ */
+static inline unsigned int uaccess_save_and_enable(void)
+{
+ return 0;
+}
+
+static inline void uaccess_restore(unsigned int flags)
+{
+}
+
+/*
* These two are intentionally not defined anywhere - if the kernel
* code generates any references to them, that's a bug.
*/
@@ -165,6 +180,7 @@
register typeof(x) __r2 asm("r2"); \
register unsigned long __l asm("r1") = __limit; \
register int __e asm("r0"); \
+ unsigned int __ua_flags = uaccess_save_and_enable(); \
switch (sizeof(*(__p))) { \
case 1: \
if (sizeof((x)) >= 8) \
@@ -192,6 +208,7 @@
break; \
default: __e = __get_user_bad(); break; \
} \
+ uaccess_restore(__ua_flags); \
x = (typeof(*(p))) __r2; \
__e; \
})
@@ -224,6 +241,7 @@
register const typeof(*(p)) __user *__p asm("r0") = __tmp_p; \
register unsigned long __l asm("r1") = __limit; \
register int __e asm("r0"); \
+ unsigned int __ua_flags = uaccess_save_and_enable(); \
switch (sizeof(*(__p))) { \
case 1: \
__put_user_x(__r2, __p, __e, __l, 1); \
@@ -239,6 +257,7 @@
break; \
default: __e = __put_user_bad(); break; \
} \
+ uaccess_restore(__ua_flags); \
__e; \
})
@@ -300,14 +319,17 @@
do { \
unsigned long __gu_addr = (unsigned long)(ptr); \
unsigned long __gu_val; \
+ unsigned int __ua_flags; \
__chk_user_ptr(ptr); \
might_fault(); \
+ __ua_flags = uaccess_save_and_enable(); \
switch (sizeof(*(ptr))) { \
case 1: __get_user_asm_byte(__gu_val, __gu_addr, err); break; \
case 2: __get_user_asm_half(__gu_val, __gu_addr, err); break; \
case 4: __get_user_asm_word(__gu_val, __gu_addr, err); break; \
default: (__gu_val) = __get_user_bad(); \
} \
+ uaccess_restore(__ua_flags); \
(x) = (__typeof__(*(ptr)))__gu_val; \
} while (0)
@@ -381,9 +403,11 @@
#define __put_user_err(x, ptr, err) \
do { \
unsigned long __pu_addr = (unsigned long)(ptr); \
+ unsigned int __ua_flags; \
__typeof__(*(ptr)) __pu_val = (x); \
__chk_user_ptr(ptr); \
might_fault(); \
+ __ua_flags = uaccess_save_and_enable(); \
switch (sizeof(*(ptr))) { \
case 1: __put_user_asm_byte(__pu_val, __pu_addr, err); break; \
case 2: __put_user_asm_half(__pu_val, __pu_addr, err); break; \
@@ -391,6 +415,7 @@
case 8: __put_user_asm_dword(__pu_val, __pu_addr, err); break; \
default: __put_user_bad(); \
} \
+ uaccess_restore(__ua_flags); \
} while (0)
#define __put_user_asm_byte(x, __pu_addr, err) \
@@ -474,11 +499,46 @@
#ifdef CONFIG_MMU
-extern unsigned long __must_check __copy_from_user(void *to, const void __user *from, unsigned long n);
-extern unsigned long __must_check __copy_to_user(void __user *to, const void *from, unsigned long n);
-extern unsigned long __must_check __copy_to_user_std(void __user *to, const void *from, unsigned long n);
-extern unsigned long __must_check __clear_user(void __user *addr, unsigned long n);
-extern unsigned long __must_check __clear_user_std(void __user *addr, unsigned long n);
+extern unsigned long __must_check
+arm_copy_from_user(void *to, const void __user *from, unsigned long n);
+
+static inline unsigned long __must_check
+__copy_from_user(void *to, const void __user *from, unsigned long n)
+{
+ unsigned int __ua_flags = uaccess_save_and_enable();
+ n = arm_copy_from_user(to, from, n);
+ uaccess_restore(__ua_flags);
+ return n;
+}
+
+extern unsigned long __must_check
+arm_copy_to_user(void __user *to, const void *from, unsigned long n);
+extern unsigned long __must_check
+__copy_to_user_std(void __user *to, const void *from, unsigned long n);
+
+static inline unsigned long __must_check
+__copy_to_user(void __user *to, const void *from, unsigned long n)
+{
+ unsigned int __ua_flags = uaccess_save_and_enable();
+ n = arm_copy_to_user(to, from, n);
+ uaccess_restore(__ua_flags);
+ return n;
+}
+
+extern unsigned long __must_check
+arm_clear_user(void __user *addr, unsigned long n);
+extern unsigned long __must_check
+__clear_user_std(void __user *addr, unsigned long n);
+
+static inline unsigned long __must_check
+__clear_user(void __user *addr, unsigned long n)
+{
+ unsigned int __ua_flags = uaccess_save_and_enable();
+ n = arm_clear_user(addr, n);
+ uaccess_restore(__ua_flags);
+ return n;
+}
+
#else
#define __copy_from_user(to, from, n) (memcpy(to, (void __force *)from, n), 0)
#define __copy_to_user(to, from, n) (memcpy((void __force *)to, from, n), 0)
@@ -511,6 +571,7 @@
return n;
}
+/* These are from lib/ code, and use __get_user() and friends */
extern long strncpy_from_user(char *dest, const char __user *src, long count);
extern __must_check long strlen_user(const char __user *str);