| From | Luis Henriques <> | Subject | [PATCH 3.16.y-ckt 126/129] arm64/mm: Remove hack in mmap randomize layout | Date | Fri, 22 May 2015 09:58:31 +0100 |
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3.16.7-ckt12 -stable review patch. If anyone has any objections, please let me know.
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From: Yann Droneaud <ydroneaud@opteya.com>
commit d6c763afab142a85e4770b4bc2a5f40f256d5c5d upstream.
Since commit 8a0a9bd4db63 ('random: make get_random_int() more random'), get_random_int() returns a random value for each call, so comment and hack introduced in mmap_rnd() as part of commit 1d18c47c735e ('arm64: MMU fault handling and page table management') are incorrects.
Commit 1d18c47c735e seems to use the same hack introduced by commit a5adc91a4b44 ('powerpc: Ensure random space between stack and mmaps'), latter copied in commit 5a0efea09f42 ('sparc64: Sharpen address space randomization calculations.').
But both architectures were cleaned up as part of commit fa8cbaaf5a68 ('powerpc+sparc64/mm: Remove hack in mmap randomize layout') as hack is no more needed since commit 8a0a9bd4db63.
So the present patch removes the comment and the hack around get_random_int() on AArch64's mmap_rnd().
Cc: David S. Miller <davem@davemloft.net> Cc: Anton Blanchard <anton@samba.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Dan McGee <dpmcgee@gmail.com> Signed-off-by: Yann Droneaud <ydroneaud@opteya.com> Signed-off-by: Will Deacon <will.deacon@arm.com> Cc: Moritz Mühlenhoff <jmm@inutil.org> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- arch/arm64/mm/mmap.c | 12 ++---------- 1 file changed, 2 insertions(+), 10 deletions(-)
diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c index 8ed6cb1a900f..8f7ffffc63e9 100644 --- a/arch/arm64/mm/mmap.c +++ b/arch/arm64/mm/mmap.c @@ -47,22 +47,14 @@ static int mmap_is_legacy(void) return sysctl_legacy_va_layout; } -/* - * Since get_random_int() returns the same value within a 1 jiffy window, we - * will almost always get the same randomisation for the stack and mmap - * region. This will mean the relative distance between stack and mmap will be - * the same. - * - * To avoid this we can shift the randomness by 1 bit. - */ static unsigned long mmap_rnd(void) { unsigned long rnd = 0; if (current->flags & PF_RANDOMIZE) - rnd = (long)get_random_int() & (STACK_RND_MASK >> 1); + rnd = (long)get_random_int() & STACK_RND_MASK; - return rnd << (PAGE_SHIFT + 1); + return rnd << PAGE_SHIFT; } static unsigned long mmap_base(void)
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