@@ -26,6 +26,8 @@ u64 __siphash_aligned(const void *data, size_t len, const siphash_key_t *key);
u64 __siphash_unaligned(const void *data, size_t len, const siphash_key_t *key);
#endif
+unsigned long siphash_1ulong(const unsigned long a, const siphash_key_t *key);
+
u64 siphash_1u64(const u64 a, const siphash_key_t *key);
u64 siphash_2u64(const u64 a, const u64 b, const siphash_key_t *key);
u64 siphash_3u64(const u64 a, const u64 b, const u64 c,
@@ -116,6 +116,19 @@ EXPORT_SYMBOL(__siphash_unaligned);
#endif
/**
+ * siphash_1ulong - computes siphash PRF value
+ * @first: value to hash
+ * @key: the siphash key
+ */
+unsigned long siphash_1ulong(const unsigned long first, const siphash_key_t *key)
+{
+#ifdef CONFIG_64BIT
+ return (unsigned long)siphash_1u64((u64)first, key);
+#endif
+ return (unsigned long)siphash_1u32((u32)first, key);
+}
+
+/**
* siphash_1u64 - compute 64-bit siphash PRF value of a u64
* @first: first u64
* @key: the siphash key
@@ -33,6 +33,7 @@
#include <linux/uuid.h>
#include <linux/of.h>
#include <net/addrconf.h>
+#include <linux/siphash.h>
#ifdef CONFIG_BLOCK
#include <linux/blkdev.h>
#endif
@@ -1591,6 +1592,25 @@ char *device_node_string(char *buf, char *end, struct device_node *dn,
return widen_string(buf, buf - buf_start, end, spec);
}
+/* Maps a pointer to a 32 bit unique identifier. */
+static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec)
+{
+ static siphash_key_t ptr_secret __read_mostly;
+ static atomic_t have_key = ATOMIC_INIT(0);
+ unsigned long hashval;
+
+ if (atomic_xchg(&have_key, 1) == 0)
+ get_random_bytes(&ptr_secret, sizeof(ptr_secret));
+
+ hashval = siphash_1ulong((unsigned long)ptr, &ptr_secret);
+
+ spec.field_width = 2 + 2 * sizeof(unsigned int); /* 0x + hex */
+ spec.flags = SPECIAL | SMALL | ZEROPAD;
+ spec.base = 16;
+
+ return number(buf, end, (u32)hashval, spec);
+}
+
int kptr_restrict __read_mostly;
/*
@@ -1703,6 +1723,9 @@ int kptr_restrict __read_mostly;
* Note: The difference between 'S' and 'F' is that on ia64 and ppc64
* function pointers are really function descriptors, which contain a
* pointer to the real address.
+ *
+ * Default behaviour (unadorned %p) is to hash the address, rendering it useful
+ * as a unique identifier.
*/
static noinline_for_stack
char *pointer(const char *fmt, char *buf, char *end, void *ptr,
@@ -1858,14 +1881,13 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
return device_node_string(buf, end, ptr, spec, fmt + 1);
}
}
- spec.flags |= SMALL;
+
if (spec.field_width == -1) {
spec.field_width = default_width;
spec.flags |= ZEROPAD;
}
- spec.base = 16;
- return number(buf, end, (unsigned long) ptr, spec);
+ return ptr_to_id(buf, end, ptr, spec);
}
/*
Currently there are many places in the kernel where addresses are being printed using an unadorned %p. Kernel pointers should be printed using %pK allowing some control via the kptr_restrict sysctl. Exposing addresses gives attackers sensitive information about the kernel layout in memory. We can reduce the attack surface by hashing all addresses printed with %p. This will of course break some users, forcing code printing needed addresses to be updated. For what it's worth, usage of unadorned %p can be broken down as follows (thanks to Joe Perches). $ git grep -E '%p[^A-Za-z0-9]' | cut -f1 -d"/" | sort | uniq -c 1084 arch 20 block 10 crypto 32 Documentation 8121 drivers 1221 fs 143 include 101 kernel 69 lib 100 mm 1510 net 40 samples 7 scripts 11 security 166 sound 152 tools 2 virt Add function ptr_to_id() to map an address to a 32 bit unique identifier. Signed-off-by: Tobin C. Harding <me@tobin.cc> --- V3: - Use atomic_xchg() to guard setting [random] key. - Remove erroneous white space change. V2: - Use SipHash to do the hashing. The discussion related to this patch has been fragmented. There are three threads associated with this patch. Email threads by subject: [PATCH] printk: hash addresses printed with %p [PATCH 0/3] add %pX specifier [kernel-hardening] [RFC V2 0/6] add more kernel pointer filter options include/linux/siphash.h | 2 ++ lib/siphash.c | 13 +++++++++++++ lib/vsprintf.c | 28 +++++++++++++++++++++++++--- 3 files changed, 40 insertions(+), 3 deletions(-)