lkml.org 
[lkml]   [2017]   [May]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 1/5] random,stackprotect: introduce get_random_canary function
Date
From: Rik van Riel <riel@redhat.com>

Introduce the get_random_canary function, which provides a random
unsigned long canary value with the first byte zeroed out on 64
bit architectures, in order to mitigate non-terminated C string
overflows.

Inspired by the "ascii armor" code in the old execshield patches,
and the current PaX/grsecurity code base.

Signed-off-by: Rik van Riel <riel@redhat.com>
---
include/linux/random.h | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)

diff --git a/include/linux/random.h b/include/linux/random.h
index ed5c3838780d..765a992c6774 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -57,6 +57,26 @@ 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);
--
2.9.3
\
 
 \ /
  Last update: 2017-05-19 23:35    [W:0.139 / U:0.544 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site