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Commit a98406e22c12e514bac28fec0a49dc793edaf3a8

Authored by Daniel Borkmann
Committed by David S. Miller
1 parent c1e60bd4fe
Exists in ti-lsk-linux-4.1.y and in 10 other branches dlt-processor-sdk-linux-03.00.00.04, processor-sdk-linux-02.00.01, smarc-ti-lsk-linux-4.1.y, smarct3x-processor-sdk-04.01.00.06, smarct3x-processor-sdk-linux-02.00.01, smarct3x-processor-sdk-linux-03.00.00.04, smarct4x-800-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-04.01.00.06, smarct4x-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-linux-03.00.00.04

random32: improvements to prandom_bytes 

This patch addresses a couple of minor items, mostly addesssing
prandom_bytes(): 1) prandom_bytes{,_state}() should use size_t
for length arguments, 2) We can use put_unaligned() when filling
the array instead of open coding it [ perhaps some archs will
further benefit from their own arch specific implementation when
GCC cannot make up for it ], 3) Fix a typo, 4) Better use unsigned
int as type for getting the arch seed, 5) Make use of
prandom_u32_max() for timer slack.

Regarding the change to put_unaligned(), callers of prandom_bytes()
which internally invoke prandom_bytes_state(), don't bother as
they expect the array to be filled randomly and don't have any
control of the internal state what-so-ever (that's also why we
have periodic reseeding there, etc), so they really don't care.

Now for the direct callers of prandom_bytes_state(), which
are solely located in test cases for MTD devices, that is,
drivers/mtd/tests/{oobtest.c,pagetest.c,subpagetest.c}:

These tests basically fill a test write-vector through
prandom_bytes_state() with an a-priori defined seed each time
and write that to a MTD device. Later on, they set up a read-vector
and read back that blocks from the device. So in the verification
phase, the write-vector is being re-setup [ so same seed and
prandom_bytes_state() called ], and then memcmp()'ed against the
read-vector to check if the data is the same.

Akinobu, Lothar and I also tested this patch and it runs through
the 3 relevant MTD test cases w/o any errors on the nandsim device
(simulator for MTD devs) for x86_64, ppc64, ARM (i.MX28, i.MX53
and i.MX6):

  # modprobe nandsim first_id_byte=0x20 second_id_byte=0xac \
                     third_id_byte=0x00 fourth_id_byte=0x15
  # modprobe mtd_oobtest dev=0
  # modprobe mtd_pagetest dev=0
  # modprobe mtd_subpagetest dev=0

We also don't have any users depending directly on a particular
result of the PRNG (except the PRNG self-test itself), and that's
just fine as it e.g. allowed us easily to do things like upgrading
from taus88 to taus113.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Tested-by: Akinobu Mita <akinobu.mita@gmail.com>
Tested-by: Lothar Waßmann <LW@KARO-electronics.de>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Showing 2 changed files with 20 additions and 23 deletions Side-by-side Diff

include/linux/random.h
Diff comments   View file @ a98406e
... ... @@ -26,7 +26,7 @@
26 26 unsigned long randomize_range(unsigned long start, unsigned long end, unsigned long len);
27 27  
28 28 u32 prandom_u32(void);
29   -void prandom_bytes(void *buf, int nbytes);
  29 +void prandom_bytes(void *buf, size_t nbytes);
30 30 void prandom_seed(u32 seed);
31 31 void prandom_reseed_late(void);
32 32  
... ... @@ -35,7 +35,7 @@
35 35 };
36 36  
37 37 u32 prandom_u32_state(struct rnd_state *state);
38   -void prandom_bytes_state(struct rnd_state *state, void *buf, int nbytes);
  38 +void prandom_bytes_state(struct rnd_state *state, void *buf, size_t nbytes);
39 39  
40 40 /**
41 41 * prandom_u32_max - returns a pseudo-random number in interval [0, ep_ro)
... ... @@ -37,6 +37,7 @@
37 37 #include <linux/jiffies.h>
38 38 #include <linux/random.h>
39 39 #include <linux/sched.h>
  40 +#include <asm/unaligned.h>
40 41  
41 42 #ifdef CONFIG_RANDOM32_SELFTEST
42 43 static void __init prandom_state_selftest(void);
43 44  
44 45  
45 46  
46 47  
... ... @@ -96,27 +97,23 @@
96 97 * This is used for pseudo-randomness with no outside seeding.
97 98 * For more random results, use prandom_bytes().
98 99 */
99   -void prandom_bytes_state(struct rnd_state *state, void *buf, int bytes)
  100 +void prandom_bytes_state(struct rnd_state *state, void *buf, size_t bytes)
100 101 {
101   - unsigned char *p = buf;
102   - int i;
  102 + u8 *ptr = buf;
103 103  
104   - for (i = 0; i < round_down(bytes, sizeof(u32)); i += sizeof(u32)) {
105   - u32 random = prandom_u32_state(state);
106   - int j;
107   -
108   - for (j = 0; j < sizeof(u32); j++) {
109   - p[i + j] = random;
110   - random >>= BITS_PER_BYTE;
111   - }
  104 + while (bytes >= sizeof(u32)) {
  105 + put_unaligned(prandom_u32_state(state), (u32 *) ptr);
  106 + ptr += sizeof(u32);
  107 + bytes -= sizeof(u32);
112 108 }
113   - if (i < bytes) {
114   - u32 random = prandom_u32_state(state);
115 109  
116   - for (; i < bytes; i++) {
117   - p[i] = random;
118   - random >>= BITS_PER_BYTE;
119   - }
  110 + if (bytes > 0) {
  111 + u32 rem = prandom_u32_state(state);
  112 + do {
  113 + *ptr++ = (u8) rem;
  114 + bytes--;
  115 + rem >>= BITS_PER_BYTE;
  116 + } while (bytes > 0);
120 117 }
121 118 }
122 119 EXPORT_SYMBOL(prandom_bytes_state);
... ... @@ -126,7 +123,7 @@
126 123 * @buf: where to copy the pseudo-random bytes to
127 124 * @bytes: the requested number of bytes
128 125 */
129   -void prandom_bytes(void *buf, int bytes)
  126 +void prandom_bytes(void *buf, size_t bytes)
130 127 {
131 128 struct rnd_state *state = &get_cpu_var(net_rand_state);
132 129  
... ... @@ -137,7 +134,7 @@
137 134  
138 135 static void prandom_warmup(struct rnd_state *state)
139 136 {
140   - /* Calling RNG ten times to satify recurrence condition */
  137 + /* Calling RNG ten times to satisfy recurrence condition */
141 138 prandom_u32_state(state);
142 139 prandom_u32_state(state);
143 140 prandom_u32_state(state);
... ... @@ -152,7 +149,7 @@
152 149  
153 150 static u32 __extract_hwseed(void)
154 151 {
155   - u32 val = 0;
  152 + unsigned int val = 0;
156 153  
157 154 (void)(arch_get_random_seed_int(&val) ||
158 155 arch_get_random_int(&val));
... ... @@ -228,7 +225,7 @@
228 225 prandom_seed(entropy);
229 226  
230 227 /* reseed every ~60 seconds, in [40 .. 80) interval with slack */
231   - expires = 40 + (prandom_u32() % 40);
  228 + expires = 40 + prandom_u32_max(40);
232 229 seed_timer.expires = jiffies + msecs_to_jiffies(expires * MSEC_PER_SEC);
233 230  
234 231 add_timer(&seed_timer);