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c40160f299
While the latent entropy plugin mostly doesn't derive entropy from
get_random_const() for measuring the call graph, when __latent_entropy is
applied to a constant, then it's initialized statically to output from
get_random_const(). In that case, this data is derived from a 64-bit
seed, which means a buffer of 512 bits doesn't really have that amount
of compile-time entropy.
This patch fixes that shortcoming by just buffering chunks of
/dev/urandom output and doling it out as requested.
At the same time, it's important that we don't break the use of
-frandom-seed, for people who want the runtime benefits of the latent
entropy plugin, while still having compile-time determinism. In that
case, we detect whether gcc's set_random_seed() has been called by
making a call to get_random_seed(noinit=true) in the plugin init
function, which is called after set_random_seed() is called but before
anything that calls get_random_seed(noinit=false), and seeing if it's
zero or not. If it's not zero, we're in deterministic mode, and so we
just generate numbers with a basic xorshift prng.
Note that we don't detect if -frandom-seed is being used using the
documented local_tick variable, because it's assigned via:
local_tick = (unsigned) tv.tv_sec * 1000 + tv.tv_usec / 1000;
which may well overflow and become -1 on its own, and so isn't
reliable: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105171
[kees: The 256 byte rnd_buf size was chosen based on average (250),
median (64), and std deviation (575) bytes of used entropy for a
defconfig x86_64 build]
Fixes:
|
||
|---|---|---|
| .. | ||
| .gitignore | ||
| arm_ssp_per_task_plugin.c | ||
| gcc-common.h | ||
| gcc-generate-gimple-pass.h | ||
| gcc-generate-ipa-pass.h | ||
| gcc-generate-rtl-pass.h | ||
| gcc-generate-simple_ipa-pass.h | ||
| gen-random-seed.sh | ||
| Kconfig | ||
| latent_entropy_plugin.c | ||
| Makefile | ||
| randomize_layout_plugin.c | ||
| sancov_plugin.c | ||
| stackleak_plugin.c | ||
| structleak_plugin.c | ||