From: Yann Droneaud Date: Mon, 17 Nov 2014 23:02:19 +0000 (+0000) Subject: arm64/mm: Remove hack in mmap randomize layout X-Git-Tag: firefly_0821_release~3679^2~151 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=82c9aed33b8a6ca79121d54f1504e9df6b0479cd;p=firefly-linux-kernel-4.4.55.git arm64/mm: Remove hack in mmap randomize layout 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 Cc: Anton Blanchard Cc: Benjamin Herrenschmidt Acked-by: Will Deacon Acked-by: Dan McGee Signed-off-by: Yann Droneaud Signed-off-by: Will Deacon Cc: Matthias Brugger Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c index 7c7be7855638..8aaf073ee078 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)