tree 53e098caca26aadb82706a88607e7d4a1d13547d
parent f4b30936b4c4212eb2cd2be1fd3f1139234f1821
author dcashman <dcashman@google.com> 1456349226 -0800
committer Kees Cook <keescook@google.com> 1458856927 -0700

FROMLIST: drivers: char: random: add get_random_long()

(cherry picked from commit https://lkml.org/lkml/2016/2/4/831)

d07e22597d1d355 ("mm: mmap: add new /proc tunable for mmap_base ASLR")
added the ability to choose from a range of values to use for entropy
count in generating the random offset to the mmap_base address.  The
maximum value on this range was set to 32 bits for 64-bit x86 systems, but
this value could be increased further, requiring more than the 32 bits of
randomness provided by get_random_int(), as is already possible for arm64.
Add a new function: get_random_long() which more naturally fits with the
mmap usage of get_random_int() but operates exactly the same as
get_random_int().

Also, fix the shifting constant in mmap_rnd() to be an unsigned long so
that values greater than 31 bits generate an appropriate mask without
overflow.  This is especially important on x86, as its shift instruction
uses a 5-bit mask for the shift operand, which meant that any value for
mmap_rnd_bits over 31 acts as a no-op and effectively disables mmap_base
randomization.

Finally, replace calls to get_random_int() with get_random_long() where
appropriate.

Signed-off-by: Daniel Cashman <dcashman@android.com>
Signed-off-by: Daniel Cashman <dcashman@google.com>

Bug: 27796957
Patchset: ASLR sysctl

Change-Id: I45b550f67bdb731afeee866e637d8a4d2ce1e053
Signed-off-by: Kees Cook <keescook@google.com>