Patch "arm64/mm: Remove hack in mmap randomize layout" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

arm64/mm: Remove hack in mmap randomize layout

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
arm64-mm-remove-hack-in-mmap-randomize-layout.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Yann Droneaud <[email protected]>
Date: Mon, 17 Nov 2014 23:02:19 +0000
Subject: arm64/mm: Remove hack in mmap randomize layout

From: Yann Droneaud <[email protected]>

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().

---
 arch/arm64/mm/mmap.c |   12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

@@ -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)

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/arm64-mm-remove-hack-in-mmap-randomize-layout.patch