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authorDaniel Cashman <dcashman@google.com>2016-01-14 15:20:06 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-01-14 16:00:49 -0800
commit9e08f57d684ac2f40685f55f659564bfd91a971e (patch)
tree8967949ecffbae925d34459887341c3caa8fe8b4 /arch
parent8f0d3aa9de57662fe35d8bacfbd9d7ef85ffe98f (diff)
downloadlinux-9e08f57d684ac2f40685f55f659564bfd91a971e.tar.bz2
x86: mm: support ARCH_MMAP_RND_BITS
x86: arch_mmap_rnd() uses hard-coded values, 8 for 32-bit and 28 for 64-bit, 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@google.com> Cc: Russell King <linux@arm.linux.org.uk> Acked-by: Kees Cook <keescook@chromium.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Don Zickus <dzickus@redhat.com> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Heinrich Schuchardt <xypron.glpk@gmx.de> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: David Rientjes <rientjes@google.com> Cc: Mark Salyzyn <salyzyn@android.com> Cc: Jeff Vander Stoep <jeffv@google.com> Cc: Nick Kralevich <nnk@google.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Hector Marco-Gisbert <hecmargi@upv.es> Cc: Borislav Petkov <bp@suse.de> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/Kconfig16
-rw-r--r--arch/x86/mm/mmap.c12
2 files changed, 22 insertions, 6 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5d2293417946..24f362bf3ec6 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -83,6 +83,8 @@ config X86
select HAVE_ARCH_KASAN if X86_64 && SPARSEMEM_VMEMMAP
select HAVE_ARCH_KGDB
select HAVE_ARCH_KMEMCHECK
+ select HAVE_ARCH_MMAP_RND_BITS if MMU
+ select HAVE_ARCH_MMAP_RND_COMPAT_BITS if MMU && COMPAT
select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ARCH_SOFT_DIRTY if X86_64
select HAVE_ARCH_TRACEHOOK
@@ -184,6 +186,20 @@ config HAVE_LATENCYTOP_SUPPORT
config MMU
def_bool y
+config ARCH_MMAP_RND_BITS_MIN
+ default 28 if 64BIT
+ default 8
+
+config ARCH_MMAP_RND_BITS_MAX
+ default 32 if 64BIT
+ default 16
+
+config ARCH_MMAP_RND_COMPAT_BITS_MIN
+ default 8
+
+config ARCH_MMAP_RND_COMPAT_BITS_MAX
+ default 16
+
config SBUS
bool
diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index 844b06d67df4..96bd1e2bffaf 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -69,14 +69,14 @@ unsigned long arch_mmap_rnd(void)
{
unsigned long rnd;
- /*
- * 8 bits of randomness in 32bit mmaps, 20 address space bits
- * 28 bits of randomness in 64bit mmaps, 40 address space bits
- */
if (mmap_is_ia32())
- rnd = (unsigned long)get_random_int() % (1<<8);
+#ifdef CONFIG_COMPAT
+ rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_compat_bits) - 1);
+#else
+ rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_bits) - 1);
+#endif
else
- rnd = (unsigned long)get_random_int() % (1<<28);
+ rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_bits) - 1);
return rnd << PAGE_SHIFT;
}