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authorTheodore Ts'o <tytso@mit.edu>2012-07-05 10:35:23 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-08-15 08:10:28 -0700
commit29aef9dee78ac45c5bd7f91434b05144ec220abd (patch)
tree16b4c0aed90542db6e0cb1d45ff2e483ee3f2eae /include
parentf5caa70697d4da107f8fd33fe74977a8ec192aaf (diff)
random: add new get_random_bytes_arch() function
commit c2557a303ab6712bb6e09447df828c557c710ac9 upstream. Create a new function, get_random_bytes_arch() which will use the architecture-specific hardware random number generator if it is present. Change get_random_bytes() to not use the HW RNG, even if it is avaiable. The reason for this is that the hw random number generator is fast (if it is present), but it requires that we trust the hardware manufacturer to have not put in a back door. (For example, an increasing counter encrypted by an AES key known to the NSA.) It's unlikely that Intel (for example) was paid off by the US Government to do this, but it's impossible for them to prove otherwise --- especially since Bull Mountain is documented to use AES as a whitener. Hence, the output of an evil, trojan-horse version of RDRAND is statistically indistinguishable from an RDRAND implemented to the specifications claimed by Intel. Short of using a tunnelling electronic microscope to reverse engineer an Ivy Bridge chip and disassembling and analyzing the CPU microcode, there's no way for us to tell for sure. Since users of get_random_bytes() in the Linux kernel need to be able to support hardware systems where the HW RNG is not present, most time-sensitive users of this interface have already created their own cryptographic RNG interface which uses get_random_bytes() as a seed. So it's much better to use the HW RNG to improve the existing random number generator, by mixing in any entropy returned by the HW RNG into /dev/random's entropy pool, but to always _use_ /dev/random's entropy pool. This way we get almost of the benefits of the HW RNG without any potential liabilities. The only benefits we forgo is the speed/performance enhancements --- and generic kernel code can't depend on depend on get_random_bytes() having the speed of a HW RNG anyway. For those places that really want access to the arch-specific HW RNG, if it is available, we provide get_random_bytes_arch(). Signed-off-by: "Theodore Ts'o" <tytso@mit.edu> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/random.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/random.h b/include/linux/random.h
index e14b4387354a..29e217a7e6d0 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -56,6 +56,7 @@ extern void add_input_randomness(unsigned int type, unsigned int code,
extern void add_interrupt_randomness(int irq, int irq_flags);
extern void get_random_bytes(void *buf, int nbytes);
+extern void get_random_bytes_arch(void *buf, int nbytes);
void generate_random_uuid(unsigned char uuid_out[16]);
#ifndef MODULE