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author | Daniel Borkmann <dborkman@redhat.com> | 2014-08-23 19:03:28 +0400 |
---|---|---|
committer | David S. Miller <davem@davemloft.net> | 2014-08-25 05:36:01 +0400 |
commit | a98406e22c12e514bac28fec0a49dc793edaf3a8 (patch) | |
tree | 3d6a14a416a5f8c61030df769a6a91ef0705f85e /lib | |
parent | c1e60bd4fe65ede0c7567d22b1e92a07b75c370f (diff) | |
download | linux-a98406e22c12e514bac28fec0a49dc793edaf3a8.tar.xz |
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>
Diffstat (limited to 'lib')
-rw-r--r-- | lib/random32.c | 39 |
1 files changed, 18 insertions, 21 deletions
diff --git a/lib/random32.c b/lib/random32.c index c9b6bf3afe0c..0bee183fa18f 100644 --- a/lib/random32.c +++ b/lib/random32.c @@ -37,6 +37,7 @@ #include <linux/jiffies.h> #include <linux/random.h> #include <linux/sched.h> +#include <asm/unaligned.h> #ifdef CONFIG_RANDOM32_SELFTEST static void __init prandom_state_selftest(void); @@ -96,27 +97,23 @@ EXPORT_SYMBOL(prandom_u32); * This is used for pseudo-randomness with no outside seeding. * For more random results, use prandom_bytes(). */ -void prandom_bytes_state(struct rnd_state *state, void *buf, int bytes) +void prandom_bytes_state(struct rnd_state *state, void *buf, size_t bytes) { - unsigned char *p = buf; - int i; - - for (i = 0; i < round_down(bytes, sizeof(u32)); i += sizeof(u32)) { - u32 random = prandom_u32_state(state); - int j; + u8 *ptr = buf; - for (j = 0; j < sizeof(u32); j++) { - p[i + j] = random; - random >>= BITS_PER_BYTE; - } + while (bytes >= sizeof(u32)) { + put_unaligned(prandom_u32_state(state), (u32 *) ptr); + ptr += sizeof(u32); + bytes -= sizeof(u32); } - if (i < bytes) { - u32 random = prandom_u32_state(state); - for (; i < bytes; i++) { - p[i] = random; - random >>= BITS_PER_BYTE; - } + if (bytes > 0) { + u32 rem = prandom_u32_state(state); + do { + *ptr++ = (u8) rem; + bytes--; + rem >>= BITS_PER_BYTE; + } while (bytes > 0); } } EXPORT_SYMBOL(prandom_bytes_state); @@ -126,7 +123,7 @@ EXPORT_SYMBOL(prandom_bytes_state); * @buf: where to copy the pseudo-random bytes to * @bytes: the requested number of bytes */ -void prandom_bytes(void *buf, int bytes) +void prandom_bytes(void *buf, size_t bytes) { struct rnd_state *state = &get_cpu_var(net_rand_state); @@ -137,7 +134,7 @@ EXPORT_SYMBOL(prandom_bytes); static void prandom_warmup(struct rnd_state *state) { - /* Calling RNG ten times to satify recurrence condition */ + /* Calling RNG ten times to satisfy recurrence condition */ prandom_u32_state(state); prandom_u32_state(state); prandom_u32_state(state); @@ -152,7 +149,7 @@ static void prandom_warmup(struct rnd_state *state) static u32 __extract_hwseed(void) { - u32 val = 0; + unsigned int val = 0; (void)(arch_get_random_seed_int(&val) || arch_get_random_int(&val)); @@ -228,7 +225,7 @@ static void __prandom_timer(unsigned long dontcare) prandom_seed(entropy); /* reseed every ~60 seconds, in [40 .. 80) interval with slack */ - expires = 40 + (prandom_u32() % 40); + expires = 40 + prandom_u32_max(40); seed_timer.expires = jiffies + msecs_to_jiffies(expires * MSEC_PER_SEC); add_timer(&seed_timer); |