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

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(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.

Bug: 26963541
Signed-off-by: Daniel Cashman <dcashman@android.com>
Signed-off-by: Daniel Cashman <dcashman@google.com>
Change-Id: Ie7552631b5db86f3482cf15e7dc916d89c1c502b
This commit is contained in:
dcashman 2016-02-24 13:27:06 -08:00 committed by Artem Borisov
parent a4d7dd9c69
commit 6f8746868e
2 changed files with 23 additions and 0 deletions
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22
drivers/char/random.c
View file

@ -1520,6 +1520,28 @@ unsigned int get_random_int(void)
return ret;
}
/*
* Same as get_random_int(), but returns unsigned long.
*/
unsigned long get_random_long(void)
{
__u32 *hash;
unsigned long ret;
if (arch_get_random_long(&ret))
return ret;
hash = get_cpu_var(get_random_int_hash);
hash[0] += current->pid + jiffies + get_cycles();
md5_transform(hash, random_int_secret);
ret = *(unsigned long *)hash;
put_cpu_var(get_random_int_hash);
return ret;
}
EXPORT_SYMBOL(get_random_long);
/*
* randomize_range() returns a start address such that
*

1
include/linux/random.h
View file

@ -72,6 +72,7 @@ extern const struct file_operations random_fops, urandom_fops;
#endif
unsigned int get_random_int(void);
unsigned long get_random_long(void);
unsigned long randomize_range(unsigned long start, unsigned long end, unsigned long len);
u32 prandom_u32(void);