random,stackprotect: introduce get_random_canary function

[linux-2.6-microblaze.git] / include / linux / random.h

diff --git a/include/linux/random.h b/include/linux/random.h
index ed5c383..1fa0dc8 100644 (file)
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -57,6 +57,27 @@ static inline unsigned long get_random_long(void)
 #endif
 }
 
+/*
+ * On 64-bit architectures, protect against non-terminated C string overflows
+ * by zeroing out the first byte of the canary; this leaves 56 bits of entropy.
+ */
+#ifdef CONFIG_64BIT
+# ifdef __LITTLE_ENDIAN
+#  define CANARY_MASK 0xffffffffffffff00UL
+# else /* big endian, 64 bits: */
+#  define CANARY_MASK 0x00ffffffffffffffUL
+# endif
+#else /* 32 bits: */
+# define CANARY_MASK 0xffffffffUL
+#endif
+
+static inline unsigned long get_random_canary(void)
+{
+       unsigned long val = get_random_long();
+
+       return val & CANARY_MASK;
+}
+
 unsigned long randomize_page(unsigned long start, unsigned long range);
 
 u32 prandom_u32(void);