x86: Unify copy_to_user() and add size checking to it

Similarly to copy_from_user(), where the range check is to
protect against kernel memory corruption, copy_to_user() can
benefit from such checking too: Here it protects against kernel
information leaks.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: <arjan@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/5265059502000078000FC4F6@nat28.tlf.novell.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index c9799ed208a8..8ec57c07b125 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -544,6 +544,8 @@ extern struct movsl_mask {
 
 unsigned long __must_check _copy_from_user(void *to, const void __user *from,
                                            unsigned n);
+unsigned long __must_check _copy_to_user(void __user *to, const void *from,
+                                         unsigned n);
 
 #ifdef CONFIG_DEBUG_STRICT_USER_COPY_CHECKS
 # define copy_user_diag __compiletime_error
@@ -553,6 +555,8 @@ unsigned long __must_check _copy_from_user(void *to, const void __user *from,
 
 extern void copy_user_diag("copy_from_user() buffer size is too small")
 copy_from_user_overflow(void);
+extern void copy_user_diag("copy_to_user() buffer size is too small")
+copy_to_user_overflow(void) __asm__("copy_from_user_overflow");
 
 #undef copy_user_diag
 
@@ -563,6 +567,11 @@ __compiletime_warning("copy_from_user() buffer size is not provably correct")
 __copy_from_user_overflow(void) __asm__("copy_from_user_overflow");
 #define __copy_from_user_overflow(size, count) __copy_from_user_overflow()
 
+extern void
+__compiletime_warning("copy_to_user() buffer size is not provably correct")
+__copy_to_user_overflow(void) __asm__("copy_from_user_overflow");
+#define __copy_to_user_overflow(size, count) __copy_to_user_overflow()
+
 #else
 
 static inline void
@@ -571,6 +580,8 @@ __copy_from_user_overflow(int size, unsigned long count)
         WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count);
 }
 
+#define __copy_to_user_overflow __copy_from_user_overflow
+
 #endif
 
 static inline unsigned long __must_check
@@ -608,7 +619,26 @@ copy_from_user(void *to, const void __user *from, unsigned long n)
         return n;
 }
 
+static inline unsigned long __must_check
+copy_to_user(void __user *to, const void *from, unsigned long n)
+{
+        int sz = __compiletime_object_size(from);
+
+        might_fault();
+
+        /* See the comment in copy_from_user() above. */
+        if (likely(sz < 0 || sz >= n))
+                n = _copy_to_user(to, from, n);
+        else if(__builtin_constant_p(n))
+                copy_to_user_overflow();
+        else
+                __copy_to_user_overflow(sz, n);
+
+        return n;
+}
+
 #undef __copy_from_user_overflow
+#undef __copy_to_user_overflow
 
 #endif /* _ASM_X86_UACCESS_H */