| Message ID | 1416265339-8138-1-git-send-email-ydroneaud@opteya.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, Nov 17, 2014 at 11:02:19PM +0000, Yann Droneaud wrote: > 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: Dan McGee <dpmcgee@gmail.com> > Cc: David S. Miller <davem@davemloft.net> > Cc: Anton Blanchard <anton@samba.org> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> > Fixes: 1d18c47c735e ('arm64: MMU fault handling and page table management') > Signed-off-by: Yann Droneaud <ydroneaud@opteya.com> > --- > arch/arm64/mm/mmap.c | 12 ++---------- > 1 file changed, 2 insertions(+), 10 deletions(-) Thanks, this looks sensible: Acked-by: Will Deacon <will.deacon@arm.com> Will
diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c index 1d73662f00ff..54922d1275b8 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)
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: Dan McGee <dpmcgee@gmail.com> Cc: David S. Miller <davem@davemloft.net> Cc: Anton Blanchard <anton@samba.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Fixes: 1d18c47c735e ('arm64: MMU fault handling and page table management') Signed-off-by: Yann Droneaud <ydroneaud@opteya.com> --- arch/arm64/mm/mmap.c | 12 ++---------- 1 file changed, 2 insertions(+), 10 deletions(-)