linux-kernel - [tip:x86/mm] x86/mm: Introduce arch_rnd() to compute 32/64 mmap random base

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Message-ID: <tip-6a0b41d1e23dd3318568461593ae5e36d966981e@git.kernel.org>
Date:   Mon, 13 Mar 2017 07:03:49 -0700
From:   tip-bot for Dmitry Safonov <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de, hpa@...or.com,
        bp@...e.de, kirill.shutemov@...ux.intel.com, luto@...nel.org,
        dsafonov@...tuozzo.com, gorcunov@...nvz.org, mingo@...nel.org
Subject: [tip:x86/mm] x86/mm: Introduce arch_rnd() to compute 32/64 mmap
 random base

Commit-ID:  6a0b41d1e23dd3318568461593ae5e36d966981e
Gitweb:     http://git.kernel.org/tip/6a0b41d1e23dd3318568461593ae5e36d966981e
Author:     Dmitry Safonov <dsafonov@...tuozzo.com>
AuthorDate: Mon, 6 Mar 2017 17:17:17 +0300
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Mon, 13 Mar 2017 14:59:22 +0100

x86/mm: Introduce arch_rnd() to compute 32/64 mmap random base

The compat (32bit) mmap() sycall issued by a 64-bit task results in a
mapping above 4GB. That's outside the compat mode address space and
prevents CRIU to restore 32bit processes from a 64bit application.

As a first step to address this, split out the address base randomizing
calculation from arch_mmap_rnd() into a helper function, which can be used
independent of mmap_ia32() based decisions.

[ tglx: Massaged changelog ]

Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Dmitry Safonov <dsafonov@...tuozzo.com>
Cc: 0x7f454c46@...il.com
Cc: linux-mm@...ck.org
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Cyrill Gorcunov <gorcunov@...nvz.org>
Cc: Borislav Petkov <bp@...e.de>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Link: http://lkml.kernel.org/r/20170306141721.9188-2-dsafonov@virtuozzo.com
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

---
 arch/x86/mm/mmap.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index 7940166..f31ed70 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -55,6 +55,14 @@ static unsigned long stack_maxrandom_size(void)
 #define MIN_GAP (128*1024*1024UL + stack_maxrandom_size())
 #define MAX_GAP (TASK_SIZE/6*5)
 
+#ifdef CONFIG_COMPAT
+# define mmap32_rnd_bits  mmap_rnd_compat_bits
+# define mmap64_rnd_bits  mmap_rnd_bits
+#else
+# define mmap32_rnd_bits  mmap_rnd_bits
+# define mmap64_rnd_bits  mmap_rnd_bits
+#endif
+
 static int mmap_is_legacy(void)
 {
 	if (current->personality & ADDR_COMPAT_LAYOUT)
@@ -66,20 +74,14 @@ static int mmap_is_legacy(void)
 	return sysctl_legacy_va_layout;
 }
 
-unsigned long arch_mmap_rnd(void)
+static unsigned long arch_rnd(unsigned int rndbits)
 {
-	unsigned long rnd;
-
-	if (mmap_is_ia32())
-#ifdef CONFIG_COMPAT
-		rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
-#else
-		rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
-#endif
-	else
-		rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
+	return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT;
+}
 
-	return rnd << PAGE_SHIFT;
+unsigned long arch_mmap_rnd(void)
+{
+	return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
 }
 
 static unsigned long mmap_base(unsigned long rnd)