[Devel] [PATCH RHEL7 COMMIT] ms/x86: Fix norandmaps/ADDR_NO_RANDOMIZE

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-514.26.1.vz7.35.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-514.26.1.vz7.35.6
------>
commit 4fa8137c41058394c9935c2d18a22c8983a948c6
Author: Oleg Nesterov <oleg at redhat.com>
Date:   Tue Aug 15 17:39:52 2017 +0200

    ms/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 at redhat.com>
    Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
    Acked-by: Kirill A. Shutemov <kirill.shutemov at linux.intel.com>
    Acked-by: Cyrill Gorcunov <gorcunov at openvz.org>
    Reviewed-by: Dmitry Safonov <dsafonov at virtuozzo.com>
    Cc: stable at vger.kernel.org
    Cc: Andy Lutomirski <luto at amacapital.net>
    Cc: Andrew Morton <akpm at linux-foundation.org>
    Cc: Borislav Petkov <bp at suse.de>
    Cc: Linus Torvalds <torvalds at linux-foundation.org>
    Link: http://lkml.kernel.org/r/20170815153952.GA1076@redhat.com
    
    (cherry picked from commit 47ac5484fd961420e5ec0bb5b972fde381f57365)
    Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
    
    Conflicts:
    	arch/x86/mm/mmap.c
---
 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 a1656c8..22026df 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -81,14 +81,14 @@ static int mmap_is_legacy(void)
 
 static unsigned long arch_rnd(unsigned int rndbits)
 {
+	if (!(current->flags & PF_RANDOMIZE))
+		return 0;
 	return ((unsigned long)get_random_int() &
 			((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);
 }