Patch "x86: Fix norandmaps/ADDR_NO_RANDOMIZE" has been added to the 4.12-stable tree

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

x86: Fix norandmaps/ADDR_NO_RANDOMIZE

to the 4.12-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:
x86-fix-norandmaps-addr_no_randomize.patch
and it can be found in the queue-4.12 subdirectory.

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

From: Oleg Nesterov <[email protected]>
Date: Tue, 15 Aug 2017 17:39:52 +0200
Subject: x86: Fix norandmaps/ADDR_NO_RANDOMIZE

From: Oleg Nesterov <[email protected]>

commit 47ac5484fd961420e5ec0bb5b972fde381f57365 upstream.

Documentation/admin-guide/kernel-parameters.txt says:

norandmaps Don't use address space randomization. Equivalent
to echo 0 > /proc/sys/kernel/randomize_va_space

but it doesn't work because arch_rnd() which is used to randomize mm->mmap_base returns a random value unconditionally. And as Kirill pointed out, ADDR_NO_RANDOMIZE is broken by the same reason.

Just shift the PF_RANDOMIZE check from arch_mmap_rnd() to arch_rnd().

---
 arch/x86/mm/mmap.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -82,13 +82,13 @@ static int mmap_is_legacy(void)
 
 static unsigned long arch_rnd(unsigned int rndbits)
 {
+	if (!(current->flags & PF_RANDOMIZE))
+		return 0;
 	return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT;
 }
 
 unsigned long arch_mmap_rnd(void)
 {
-	if (!(current->flags & PF_RANDOMIZE))
-		return 0;
 	return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
 }
 

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

queue-4.12/x86-elf-remove-the-unnecessary-addr_no_randomize-checks.patch queue-4.12/mm-fix-double-mmap_sem-unlock-on-mmf_unstable-enforced-sigbus.patch queue-4.12/x86-fix-norandmaps-addr_no_randomize.patch