Re: [PATCH 0/2] Fix mmap_base entropy for >31 bits.
From: Daniel Cashman
Date: Wed Feb 24 2016 - 15:40:49 EST
On 02/04/2016 02:29 PM, Kees Cook wrote:
> On Thu, Feb 4, 2016 at 2:06 PM, Daniel Cashman <dcashman@xxxxxxxxxxx> wrote:
>> Upstream commit: d07e22597d1d355829b7b18ac19afa912cf758d1 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
>> Finally, replace calls to get_random_int() with get_random_long() where
>> Daniel Cashman (2):
>> drivers: char: random: Add get_random_long().
>> use get_random_long().
>> arch/arm/mm/mmap.c | 2 +-
>> arch/arm64/mm/mmap.c | 4 ++--
>> arch/mips/mm/mmap.c | 4 ++--
>> arch/powerpc/kernel/process.c | 4 ++--
>> arch/powerpc/mm/mmap.c | 4 ++--
>> arch/sparc/kernel/sys_sparc_64.c | 2 +-
>> arch/x86/mm/mmap.c | 6 +++---
>> drivers/char/random.c | 22 ++++++++++++++++++++++
>> fs/binfmt_elf.c | 2 +-
>> include/linux/random.h | 1 +
>> 10 files changed, 37 insertions(+), 14 deletions(-)
> Thanks for fixing this!
> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
This has now been in linux-next for awhile. Could we please submit this
for the 4.5 rc window so that it fixes the issue in the final 4.5
release? Sorry if this is a protocol breach, but I'm not sure what the
best way is for me to indicate that this is a "fix" that should go out
in the same release as the original feature.