Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1258441

[PATCH 2/2] arm: mm: support ARCH_MMAP_RND_BITS.

Show all headers | View raw

From: dcashman <dcashman@google.com>

arm: arch_mmap_rnd() uses a hard-code value of 8 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 8 as the minimum acceptable value.

Signed-off-by: Daniel Cashman <dcashman@google.com>
---
 arch/arm/Kconfig   | 24 ++++++++++++++++++++++++
 arch/arm/mm/mmap.c |  7 +++++--
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 639411f..d61e7e2 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -306,6 +306,30 @@ config MMU
 	  Select if you want MMU-based virtualised addressing space
 	  support by paged memory management. If unsure, say 'Y'.
 
+config ARCH_MMAP_RND_BITS_MIN
+	int
+	default 8
+
+config ARCH_MMAP_RND_BITS_MAX
+	int
+	default 14 if MMU && PAGE_OFFSET=0x40000000
+	default 15 if MMU && PAGE_OFFSET=0x80000000
+	default 16 if MMU
+	default 8
+
+config ARCH_MMAP_RND_BITS
+	int "Number of bits to use for ASLR of mmap base address" if EXPERT
+	range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
+	default ARCH_MMAP_RND_BITS_MIN
+	help
+	  This value can be used to select the number of bits to use to
+	  determine the random offset to the base address of vma regions
+	  resulting from mmap allocations. This value will be bounded
+	  by the architecture's minimum and maximum supported values.
+
+	  This value can be changed after boot using the
+	  /proc/sys/kernel/mmap_rnd_bits tunable
+
 #
 # The "ARM system type" choice list is ordered alphabetically by option
 # text.  Please add new entries in the option alphabetic order.
diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
index 407dc78..73ca3a7 100644
--- a/arch/arm/mm/mmap.c
+++ b/arch/arm/mm/mmap.c
@@ -11,6 +11,10 @@
 #include <linux/random.h>
 #include <asm/cachetype.h>
 
+int mmap_rnd_bits_min = CONFIG_ARCH_MMAP_RND_BITS_MIN;
+int mmap_rnd_bits_max = CONFIG_ARCH_MMAP_RND_BITS_MAX;
+int mmap_rnd_bits = CONFIG_ARCH_MMAP_RND_BITS;
+
 #define COLOUR_ALIGN(addr,pgoff)		\
 	((((addr)+SHMLBA-1)&~(SHMLBA-1)) +	\
 	 (((pgoff)<<PAGE_SHIFT) & (SHMLBA-1)))
@@ -173,8 +177,7 @@ unsigned long arch_mmap_rnd(void)
 {
 	unsigned long rnd;
 
-	/* 8 bits of randomness in 20 address space bits */
-	rnd = (unsigned long)get_random_int() % (1 << 8);
+	rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits);
 
 	return rnd << PAGE_SHIFT;
 }
-- 
2.6.0.rc2.230.g3dd15c0

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 1/2] mm: mmap: Add new /proc tunable for mmap_base ASLR. Daniel Cashman <dcashman@android.com> - 2015-10-28 22:30 +0100
  [PATCH 2/2] arm: mm: support ARCH_MMAP_RND_BITS. Daniel Cashman <dcashman@android.com> - 2015-10-28 22:30 +0100
  Re: [PATCH 1/2] mm: mmap: Add new /proc tunable for mmap_base ASLR. ebiederm@xmission.com (Eric W. Biederman) - 2015-10-29 00:50 +0100
    Re: [PATCH 1/2] mm: mmap: Add new /proc tunable for mmap_base ASLR. Jeffrey Vander Stoep <jeffv@google.com> - 2015-10-29 01:10 +0100
      Re: [PATCH 1/2] mm: mmap: Add new /proc tunable for mmap_base ASLR. Dan Cashman <dcashman@android.com> - 2015-10-29 01:40 +0100
        Re: [PATCH 1/2] mm: mmap: Add new /proc tunable for mmap_base ASLR. ebiederm@xmission.com (Eric W. Biederman) - 2015-10-29 05:00 +0100
          Re: [PATCH 1/2] mm: mmap: Add new /proc tunable for mmap_base ASLR. Daniel Cashman <dcashman@android.com> - 2015-10-29 23:10 +0100

csiph-web