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authorYann Droneaud <ydroneaud@opteya.com>2014-11-17 23:02:19 +0000
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-09-13 09:07:59 -0700
commit82c9aed33b8a6ca79121d54f1504e9df6b0479cd (patch)
treef38367970d4b6e78c68e3ce5c44ea72a4e20b7cd
parentd51689e20adbf8fe2c3999939da8d61ed2ccbc58 (diff)
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 <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: Matthias Brugger <mbrugger@suse.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--arch/arm64/mm/mmap.c12
1 files changed, 2 insertions, 10 deletions
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)