Hi Daniel, On Tue, Dec 01, 2015 at 12:10:57PM -0800, Daniel Cashman wrote: > From: dcashman <dcashman@xxxxxxxxxx> > > 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@xxxxxxxxxxx> > --- > arch/arm64/Kconfig | 31 +++++++++++++++++++++++++++++++ > arch/arm64/mm/mmap.c | 8 ++++++-- > 2 files changed, 37 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 871f217..fb57649 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 if MMU > + select HAVE_ARCH_MMAP_RND_COMPAT_BITS if MMU && COMPAT You can drop the 'if MMU' bits, since we don't support !MMU on arm64. > select HAVE_ARCH_SECCOMP_FILTER > select HAVE_ARCH_TRACEHOOK > select HAVE_BPF_JIT > @@ -104,6 +106,35 @@ config ARCH_PHYS_ADDR_T_64BIT > config MMU > def_bool y > > +config ARCH_MMAP_RND_BITS_MIN > + default 15 if ARM64_64K_PAGES > + default 17 if ARM64_16K_PAGES > + default 19 Is this correct? We currently have a mask of 0x3ffff, so that's 18 bits. > +config ARCH_MMAP_RND_BITS_MAX > + default 19 if ARM64_VA_BITS=36 > + default 20 if ARM64_64K_PAGES && ARM64_VA_BITS=39 > + default 22 if ARM64_16K_PAGES && ARM64_VA_BITS=39 > + default 24 if ARM64_VA_BITS=39 > + default 23 if ARM64_64K_PAGES && ARM64_VA_BITS=42 > + default 25 if ARM64_16K_PAGES && ARM64_VA_BITS=42 > + default 27 if ARM64_VA_BITS=42 > + default 30 if ARM64_VA_BITS=47 > + default 29 if ARM64_64K_PAGES && ARM64_VA_BITS=48 > + default 31 if ARM64_16K_PAGES && ARM64_VA_BITS=48 > + default 33 if ARM64_VA_BITS=48 > + default 15 if ARM64_64K_PAGES > + default 17 if ARM64_16K_PAGES > + default 19 Could you add a comment above this with the formula (VA_BITS - PAGE_SHIFT - 3), please, so that we can update this easily in the future if we need to? Will -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>