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

(cherry picked from commit

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

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

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

Signed-off-by: Daniel Cashman <>
Signed-off-by: Daniel Cashman <>

Bug: 27796957
Patchset: ASLR sysctl

Change-Id: I45b550f67bdb731afeee866e637d8a4d2ce1e053
Signed-off-by: Kees Cook <>
2 files changed