BACKPORT: printk: hash addresses printed with %p
Currently there exist approximately 14 000 places in the kernel where
addresses are being printed using an unadorned %p. This potentially
leaks sensitive information regarding the Kernel layout in memory. Many
of these calls are stale, instead of fixing every call lets hash the
address by default before printing. This will of course break some
users, forcing code printing needed addresses to be updated.
Code that _really_ needs the address will soon be able to use the new
printk specifier %px to print the address.
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. Hash any unadorned usage of specifier %p and any malformed
specifiers.
Signed-off-by: Tobin C. Harding <me@tobin.cc>
(cherry picked from commit ad67b74d2469d9b82aaa572d76474c95bc484d57)
Signed-off-by: Sandeep Patil <sspatil@android.com>
Bug: 78533979
Test: Build and boot cuttlefish
Test: Runtime tests by enabling CONFIG_TEST_PRINTF
Change-Id: I4a12d890d7b22caa502280d78cb4f6a09c866471
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index a3ba9a5..ced3289 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -32,6 +32,8 @@
#include <linux/cred.h>
#include <linux/uuid.h>
#include <net/addrconf.h>
+#include <linux/siphash.h>
+#include <linux/compiler.h>
#ifdef CONFIG_BLOCK
#include <linux/blkdev.h>
#endif
@@ -1520,6 +1522,73 @@
return format_flags(buf, end, flags, names);
}
+static bool have_filled_random_ptr_key __read_mostly;
+static siphash_key_t ptr_key __read_mostly;
+
+static void fill_random_ptr_key(struct random_ready_callback *unused)
+{
+ get_random_bytes(&ptr_key, sizeof(ptr_key));
+ /*
+ * have_filled_random_ptr_key==true is dependent on get_random_bytes().
+ * ptr_to_id() needs to see have_filled_random_ptr_key==true
+ * after get_random_bytes() returns.
+ */
+ smp_mb();
+ WRITE_ONCE(have_filled_random_ptr_key, true);
+}
+
+static struct random_ready_callback random_ready = {
+ .func = fill_random_ptr_key
+};
+
+static int __init initialize_ptr_random(void)
+{
+ int ret = add_random_ready_callback(&random_ready);
+
+ if (!ret) {
+ return 0;
+ } else if (ret == -EALREADY) {
+ fill_random_ptr_key(&random_ready);
+ return 0;
+ }
+
+ return ret;
+}
+early_initcall(initialize_ptr_random);
+
+/* Maps a pointer to a 32 bit unique identifier. */
+static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec)
+{
+ unsigned long hashval;
+ const int default_width = 2 * sizeof(ptr);
+
+ if (unlikely(!have_filled_random_ptr_key)) {
+ spec.field_width = default_width;
+ /* string length must be less than default_width */
+ return string(buf, end, "(ptrval)", spec);
+ }
+
+#ifdef CONFIG_64BIT
+ hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key);
+ /*
+ * Mask off the first 32 bits, this makes explicit that we have
+ * modified the address (and 32 bits is plenty for a unique ID).
+ */
+ hashval = hashval & 0xffffffff;
+#else
+ hashval = (unsigned long)siphash_1u32((u32)ptr, &ptr_key);
+#endif
+
+ spec.flags |= SMALL;
+ if (spec.field_width == -1) {
+ spec.field_width = default_width;
+ spec.flags |= ZEROPAD;
+ }
+ spec.base = 16;
+
+ return number(buf, end, hashval, spec);
+}
+
/*
* Show a '%p' thing. A kernel extension is that the '%p' is followed
* by an extra set of alphanumeric characters that are extended format
@@ -1617,6 +1686,9 @@
* 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.
+ *
+ * Note: The 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,
@@ -1727,14 +1799,9 @@
case 'G':
return flags_string(buf, end, ptr, fmt);
}
- 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);
+ /* default is to _not_ leak addresses, hash before printing */
+ return ptr_to_id(buf, end, ptr, spec);
}
/*