From: Daniel Cashman <dcashman@...>

commit 8f0d3aa9de57662fe35d8bacfbd9d7ef85ffe98f upstream.

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@...>
Cc: Russell King <linux@...>
Acked-by: Kees Cook <keescook@...>
Cc: Ingo Molnar <mingo@...>
Cc: Jonathan Corbet <corbet@...>
Cc: Don Zickus <dzickus@...>
Cc: Eric W. Biederman <ebiederm@...>
Cc: Heinrich Schuchardt <xypron.glpk@...>
Cc: Josh Poimboeuf <jpoimboe@...>
Cc: Kirill A. Shutemov <kirill.shutemov@...>
Cc: Naoya Horiguchi <n-horiguchi@...>
Cc: Andrea Arcangeli <aarcange@...>
Cc: Mel Gorman <mgorman@...>
Cc: Thomas Gleixner <tglx@...>
Cc: David Rientjes <rientjes@...>
Cc: Mark Salyzyn <salyzyn@...>
Cc: Jeff Vander Stoep <jeffv@...>
Cc: Nick Kralevich <nnk@...>
Cc: Catalin Marinas <catalin.marinas@...>
Cc: Will Deacon <will.deacon@...>
Cc: "H. Peter Anvin" <hpa@...>
Cc: Hector Marco-Gisbert <hecmargi@...>
Cc: Borislav Petkov <bp@...>
Cc: Ralf Baechle <ralf@...>
Cc: Heiko Carstens <heiko.carstens@...>
Cc: Martin Schwidefsky <schwidefsky@...>
Cc: Benjamin Herrenschmidt <benh@...>
Signed-off-by: Andrew Morton <akpm@...>
Signed-off-by: Linus Torvalds <torvalds@...>
Signed-off-by: Ben Hutchings <ben.hutchings@...>
---
arch/arm64/Kconfig | 29 +++++++++++++++++++++++++++++
arch/arm64/mm/mmap.c | 8 ++++++--
2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 14cdc6dea493..edf62be35adc 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 && !(ARM64_16K_PAGES && ARM64_VA_BITS_48)
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 +106,33 @@ config ARCH_PHYS_ADDR_T_64BIT
config MMU
def_bool y

+config ARCH_MMAP_RND_BITS_MIN
+ default 14 if ARM64_64K_PAGES
+ default 16 if ARM64_16K_PAGES
+ default 18
+
+# max bits determined by the following formula:
+# VA_BITS - PAGE_SHIFT - 3
+config ARCH_MMAP_RND_BITS_MAX
+ default 19 if ARM64_VA_BITS=36
+ default 24 if ARM64_VA_BITS=39
+ default 27 if ARM64_VA_BITS=42
+ default 30 if ARM64_VA_BITS=47
+ default 29 if ARM64_VA_BITS=48 && ARM64_64K_PAGES
+ default 31 if ARM64_VA_BITS=48 && ARM64_16K_PAGES
+ default 33 if ARM64_VA_BITS=48
+ default 14 if ARM64_64K_PAGES
+ default 16 if ARM64_16K_PAGES
+ default 18
+
+config ARCH_MMAP_RND_COMPAT_BITS_MIN
+ default 7 if ARM64_64K_PAGES
+ default 9 if ARM64_16K_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 ed177475dd8c..4c893b5189dd 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -51,8 +51,12 @@ unsigned long arch_mmap_rnd(void)
{
unsigned long rnd;

- rnd = (unsigned long)get_random_int() & STACK_RND_MASK;
-
+#ifdef CONFIG_COMPAT
+ if (test_thread_flag(TIF_32BIT))
+ rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_compat_bits) - 1);
+ else
+#endif
+ rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_bits) - 1);
return rnd << PAGE_SHIFT;
}

--
2.10.2



--
Ben Hutchings
Software Developer, Codethink Ltd.