linux-kernel - [PATCH v3 3/4] arm64: mm: support ARCH_MMAP_RND

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Message-Id: <1447888808-31571-4-git-send-email-dcashman@android.com>
Date:	Wed, 18 Nov 2015 15:20:07 -0800
From:	Daniel Cashman <dcashman@...roid.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux@....linux.org.uk, akpm@...ux-foundation.org,
	keescook@...omium.org, mingo@...nel.org,
	linux-arm-kernel@...ts.infradead.org, corbet@....net,
	dzickus@...hat.com, ebiederm@...ssion.com, xypron.glpk@....de,
	jpoimboe@...hat.com, kirill.shutemov@...ux.intel.com,
	n-horiguchi@...jp.nec.com, aarcange@...hat.com, mgorman@...e.de,
	tglx@...utronix.de, rientjes@...gle.com, linux-mm@...ck.org,
	linux-doc@...r.kernel.org, salyzyn@...roid.com, jeffv@...gle.com,
	nnk@...gle.com, catalin.marinas@....com, will.deacon@....com,
	hpa@...or.com, x86@...nel.org, hecmargi@....es, bp@...e.de,
	dcashman@...gle.com
Subject: [PATCH v3 3/4] arm64: mm: support ARCH_MMAP_RND_BITS.

From: dcashman <dcashman@...gle.com>

arm64: arch_mmap_rnd() uses STACK_RND_MASK to generate the
random offset for the mmap base address.  This value represents a
compromise between increased ASLR effectiveness and avoiding
address-space fragmentation. Replace it with a Kconfig option, which
is sensibly bounded, so that platform developers may choose where to
place this compromise. Keep default values as new minimums.

Signed-off-by: Daniel Cashman <dcashman@...gle.com>
---
 arch/arm64/Kconfig   | 23 +++++++++++++++++++++++
 arch/arm64/mm/mmap.c |  6 ++++--
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 9ac16a4..be38e4c 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -51,6 +51,8 @@ config ARM64
 	select HAVE_ARCH_JUMP_LABEL
 	select HAVE_ARCH_KASAN if SPARSEMEM_VMEMMAP
 	select HAVE_ARCH_KGDB
+	select HAVE_ARCH_MMAP_RND_BITS
+	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_BPF_JIT
@@ -104,6 +106,27 @@ config ARCH_PHYS_ADDR_T_64BIT
 config MMU
 	def_bool y
 
+config ARCH_MMAP_RND_BITS_MIN
+       default 15 if ARM64_64K_PAGES
+       default 19
+
+config ARCH_MMAP_RND_BITS_MAX
+       default 20 if ARM64_64K_PAGES && ARCH_VA_BITS=39
+       default 24 if ARCH_VA_BITS=39
+       default 23 if ARM64_64K_PAGES && ARCH_VA_BITS=42
+       default 27 if ARCH_VA_BITS=42
+       default 29 if ARM64_64K_PAGES && ARCH_VA_BITS=48
+       default 33 if ARCH_VA_BITS=48
+       default 15 if ARM64_64K_PAGES
+       default 19
+
+config ARCH_MMAP_RND_COMPAT_BITS_MIN
+       default 7 if ARM64_64K_PAGES
+       default 11
+
+config ARCH_MMAP_RND_COMPAT_BITS_MAX
+       default 16
+
 config NO_IOPORT_MAP
 	def_bool y if !PCI
 
diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index ed17747..b84d5b1 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -51,8 +51,10 @@ unsigned long arch_mmap_rnd(void)
 {
 	unsigned long rnd;
 
-	rnd = (unsigned long)get_random_int() & STACK_RND_MASK;
-
+	if (test_thread_flag(TIF_32BIT))
+		rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_compat_bits);
+	else
+		rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits);
 	return rnd << PAGE_SHIFT;
 }
 
-- 
2.6.0.rc2.230.g3dd15c0

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