From: Oleg Nesterov <oleg@redhat.com>
Date: Tue, 15 Aug 2017 15:39:52 +0000 (+0200)
Subject: x86: Fix norandmaps/ADDR_NO_RANDOMIZE
X-Git-Tag: v4.12.9~12
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=932769e10de9f8b46707af8ee95ae507cba58b2e;p=thirdparty%2Fkernel%2Fstable.git

x86: Fix norandmaps/ADDR_NO_RANDOMIZE

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().

Fixes: 1b028f784e8c ("x86/mm: Introduce mmap_compat_base() for 32-bit mmap()")
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Reviewed-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20170815153952.GA1076@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index 19ad095b41dfc..6369d04fd5d62 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -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);
 }