Hi Sandy, > On Wed, 22 May 2013 13:40:04 -0400 > Sandy Harris <sandyinch...@gmail.com> wrote: > [...] > > > > >> > What I'm against is relying only on solutions such as HAVEGE or > > >> > replacing /dev/random with something scheme that only relies on > > >> > CPU timing and ignores interrupt timing. > > >> > > >> My question is how to incorporate some of that into /dev/random. > > >> At one point, timing info was used along with other stuff. Some > > >> of that got deleted later, What is the current state? Should we > > >> add more? > > > > > > Again, I would like to suggest that we look beyond a central > > > entropy collector like /dev/random. I would like to suggest to > > > consider decentralizing the collection of entropy. > > > > I'm with Ted on this one. > > When you want to consider the jitter RNG for /dev/random, it should be > used as a seed source similar to the add_*_randomness functions. I > could implement a suggestion if that is the wish. For example, such a > seed source could be triggered if the entropy estimator of the > input_pool falls below some threshold. The jitter RNG could be used to > top the entropy off to some level above another threshold.
Please see a possible integration of the CPU Jitter RNG into /dev/random as follows. The patch does not contain the jitterentropy-base.c, jitterentropy.h and jitterentropy-base-kernel.h from the tarball available at http://www.chronox.de. This patch would only use the CPU Jitter RNG if there is no more entropy in the entropy pool. Thus, the CPU Jitter RNG is only used as a fallback. The patch is tested with 3.9. Signed-off-by: Stephan Mueller <smuel...@chronox.de> --- diff -urNp linux-3.9.orig/drivers/char/Makefile linux-3.9/drivers/char/Makefile --- linux-3.9.orig/drivers/char/Makefile 2013-05-22 20:55:58.547094987 +0200 +++ linux-3.9/drivers/char/Makefile 2013-05-22 22:11:32.975008931 +0200 @@ -2,7 +2,7 @@ # Makefile for the kernel character device drivers. # -obj-y += mem.o random.o +obj-y += mem.o random.o jitterentropy-base.o obj-$(CONFIG_TTY_PRINTK) += ttyprintk.o obj-y += misc.o obj-$(CONFIG_ATARI_DSP56K) += dsp56k.o diff -urNp linux-3.9.orig/drivers/char/random.c linux-3.9/drivers/char/random.c --- linux-3.9.orig/drivers/char/random.c 2013-05-22 20:55:58.675094985 +0200 +++ linux-3.9/drivers/char/random.c 2013-05-23 11:26:25.214103807 +0200 @@ -269,6 +269,8 @@ #define CREATE_TRACE_POINTS #include <trace/events/random.h> +#include "jitterentropy.h" + /* * Configuration information */ @@ -435,6 +437,8 @@ struct entropy_store { unsigned int initialized:1; bool last_data_init; __u8 last_data[EXTRACT_SIZE]; + int jent_enable; + struct rand_data entropy_collector; }; static __u32 input_pool_data[INPUT_POOL_WORDS]; @@ -446,7 +450,8 @@ static struct entropy_store input_pool = .name = "input", .limit = 1, .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock), - .pool = input_pool_data + .pool = input_pool_data, + .jent_enable = -1 }; static struct entropy_store blocking_pool = { @@ -455,7 +460,8 @@ static struct entropy_store blocking_poo .limit = 1, .pull = &input_pool, .lock = __SPIN_LOCK_UNLOCKED(blocking_pool.lock), - .pool = blocking_pool_data + .pool = blocking_pool_data, + .jent_enable = -1 }; static struct entropy_store nonblocking_pool = { @@ -463,7 +469,8 @@ static struct entropy_store nonblocking_ .name = "nonblocking", .pull = &input_pool, .lock = __SPIN_LOCK_UNLOCKED(nonblocking_pool.lock), - .pool = nonblocking_pool_data + .pool = nonblocking_pool_data, + .jent_enable = -1 }; static __u32 const twist_table[8] = { @@ -633,6 +640,47 @@ struct timer_rand_state { unsigned dont_count_entropy:1; }; +/* lock of the entropy_store must already been taken */ +void add_jent_randomness(struct entropy_store *r) +{ +#define JENTBLOCKSIZE 8 /* the most efficient use of the CPU jitter RNG is a block + aligned invocation. The block size of the CPU jitter RNG + is 8 bytes */ + char rand[JENTBLOCKSIZE]; + int ret = 0; + + /* the initialization process determines that we cannot use the + * CPU Jitter RNG */ + if(!r->jent_enable) + return; + memset(rand, 0, JENTBLOCKSIZE); + if(-1 == r->jent_enable) + { + /* we are uninitialized, try to initialize */ + if(jent_entropy_init()) + { + /* there is no CPU Jitter, disable the entropy collector */ + r->jent_enable = 0; + return; + } + /* we do not use jent_entropy_collector_alloc as we are in early + * boot */ + memset(&r->entropy_collector, 0, sizeof(struct rand_data)); + /* initialize the entropy collector */ + jent_read_entropy(&r->entropy_collector, rand, JENTBLOCKSIZE); + r->jent_enable = 1; + } + ret = jent_read_entropy(&r->entropy_collector, rand, JENTBLOCKSIZE); + if(JENTBLOCKSIZE == ret) + { + /* we do not need to worry about trickle threshold as we are called + * when we are low on entropy */ + _mix_pool_bytes(r, rand, JENTBLOCKSIZE, NULL); + credit_entropy_bits(r, JENTBLOCKSIZE * 8); + } + memset(rand, 0, JENTBLOCKSIZE); +} + /* * Add device- or boot-specific data to the input and nonblocking * pools to help initialize them to unique values. @@ -862,6 +910,10 @@ static size_t account(struct entropy_sto nbytes * 8, r->name); /* Can we pull enough? */ + /* XXX shall we limit this call to r->limit? */ + if (r->entropy_count / 8 < min + reserved) + add_jent_randomness(r); + if (r->entropy_count / 8 < min + reserved) { nbytes = 0; } else { -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
