x86: Use __builtin_object_size() to validate the buffer size for copy_from_user()

gcc (4.x) supports the __builtin_object_size() builtin, which
reports the size of an object that a pointer point to, when known
at compile time. If the buffer size is not known at compile time, a
constant -1 is returned.

This patch uses this feature to add a sanity check to
copy_from_user(); if the target buffer is known to be smaller than
the copy size, the copy is aborted and a WARNing is emitted in
memory debug mode.

These extra checks compile away when the object size is not known,
or if both the buffer size and the copy length are constants.
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
LKML-Reference: <20090926143301.2c396b94@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/include/asm/uaccess_32.h

@@ -187,9 +187,26 @@ __copy_from_user_inatomic_nocache(void *to, const void __user *from,
 
 unsigned long __must_check copy_to_user(void __user *to,
 					const void *from, unsigned long n);
-unsigned long __must_check copy_from_user(void *to,
+unsigned long __must_check _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)
+{
+	int sz = __compiletime_object_size(to);
+	int ret = -EFAULT;
+
+	if (likely(sz == -1 || sz >= n))
+		ret = _copy_from_user(to, from, n);
+#ifdef CONFIG_DEBUG_VM
+	else
+		WARN(1, "Buffer overflow detected!\n");
+#endif
+	return ret;
+}
+
 long __must_check strncpy_from_user(char *dst, const char __user *src,
 				    long count);
 long __must_check __strncpy_from_user(char *dst,

arch/x86/include/asm/uaccess_64.h

@@ -21,10 +21,27 @@ copy_user_generic(void *to, const void *from, unsigned len);
 __must_check unsigned long
 copy_to_user(void __user *to, const void *from, unsigned len);
 __must_check unsigned long
-copy_from_user(void *to, const void __user *from, unsigned len);
+_copy_from_user(void *to, const void __user *from, unsigned len);
 __must_check unsigned long
 copy_in_user(void __user *to, const void __user *from, unsigned len);
 
+static inline unsigned long __must_check copy_from_user(void *to,
+					  const void __user *from,
+					  unsigned long n)
+{
+	int sz = __compiletime_object_size(to);
+	int ret = -EFAULT;
+
+	if (likely(sz == -1 || sz >= n))
+		ret = _copy_from_user(to, from, n);
+#ifdef CONFIG_DEBUG_VM
+	else
+		WARN(1, "Buffer overflow detected!\n");
+#endif
+	return ret;
+}
+
+
 static __always_inline __must_check
 int __copy_from_user(void *dst, const void __user *src, unsigned size)
 {

arch/x86/kernel/x8664_ksyms_64.c

@@ -30,7 +30,7 @@ EXPORT_SYMBOL(__put_user_8);
 
 EXPORT_SYMBOL(copy_user_generic);
 EXPORT_SYMBOL(__copy_user_nocache);
-EXPORT_SYMBOL(copy_from_user);
+EXPORT_SYMBOL(_copy_from_user);
 EXPORT_SYMBOL(copy_to_user);
 EXPORT_SYMBOL(__copy_from_user_inatomic);
 

arch/x86/lib/copy_user_64.S

@@ -78,7 +78,7 @@ ENTRY(copy_to_user)
 ENDPROC(copy_to_user)
 
 /* Standard copy_from_user with segment limit checking */
-ENTRY(copy_from_user)
+ENTRY(_copy_from_user)
 	CFI_STARTPROC
 	GET_THREAD_INFO(%rax)
 	movq %rsi,%rcx
@@ -88,7 +88,7 @@ ENTRY(copy_from_user)
 	jae bad_from_user
 	ALTERNATIVE_JUMP X86_FEATURE_REP_GOOD,copy_user_generic_unrolled,copy_user_generic_string
 	CFI_ENDPROC
-ENDPROC(copy_from_user)
+ENDPROC(_copy_from_user)
 
 ENTRY(copy_user_generic)
 	CFI_STARTPROC

arch/x86/lib/usercopy_32.c

@@ -874,7 +874,7 @@ EXPORT_SYMBOL(copy_to_user);
  * data to the requested size using zero bytes.
  */
 unsigned long
-copy_from_user(void *to, const void __user *from, unsigned long n)
+_copy_from_user(void *to, const void __user *from, unsigned long n)
 {
 	if (access_ok(VERIFY_READ, from, n))
 		n = __copy_from_user(to, from, n);
@@ -882,4 +882,4 @@ copy_from_user(void *to, const void __user *from, unsigned long n)
 		memset(to, 0, n);
 	return n;
 }
-EXPORT_SYMBOL(copy_from_user);
+EXPORT_SYMBOL(_copy_from_user);

include/linux/compiler-gcc4.h

@@ -37,3 +37,5 @@
 #define __cold			__attribute__((__cold__))
 
 #endif
+
+#define __compiletime_object_size(obj) __builtin_object_size(obj, 0)

include/linux/compiler.h

@@ -266,6 +266,10 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
 # define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
 #endif
 
+/* Compile time object size, -1 for unknown */
+#ifndef __compiletime_object_size
+# define __compiletime_object_size(obj) -1
+#endif
 /*
  * Prevent the compiler from merging or refetching accesses.  The compiler
  * is also forbidden from reordering successive instances of ACCESS_ONCE(),