linux-kernel - [tip:x86/urgent] x86: Fix norandmaps/ADDR_NO

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Date:   Wed, 16 Aug 2017 11:36:49 -0700
From:   tip-bot for Oleg Nesterov <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kirill.shutemov@...ux.intel.com,
        hpa@...or.com, oleg@...hat.com, tglx@...utronix.de,
        akpm@...ux-foundation.org, gorcunov@...nvz.org,
        luto@...capital.net, torvalds@...ux-foundation.org,
        mingo@...nel.org, bp@...e.de, dsafonov@...tuozzo.com
Subject: [tip:x86/urgent] x86: Fix norandmaps/ADDR_NO_RANDOMIZE

Commit-ID:  47ac5484fd961420e5ec0bb5b972fde381f57365
Gitweb:     http://git.kernel.org/tip/47ac5484fd961420e5ec0bb5b972fde381f57365
Author:     Oleg Nesterov <oleg@...hat.com>
AuthorDate: Tue, 15 Aug 2017 17:39:52 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Wed, 16 Aug 2017 20:32:01 +0200

x86: Fix norandmaps/ADDR_NO_RANDOMIZE

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().

Fixes: 1b028f784e8c ("x86/mm: Introduce mmap_compat_base() for 32-bit mmap()")
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Acked-by: Cyrill Gorcunov <gorcunov@...nvz.org>
Reviewed-by: Dmitry Safonov <dsafonov@...tuozzo.com>
Cc: stable@...r.kernel.org
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Borislav Petkov <bp@...e.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: http://lkml.kernel.org/r/20170815153952.GA1076@redhat.com

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

diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index 229d04a..c94df12 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -79,13 +79,13 @@ 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);
 }