[PATCH v5 3/4] arm64: mm: support ARCH_MMAP_RND_BITS.
From: Will Deacon <hidden>
Date: 2015-12-03 12:17:17
Also in:
linux-mm, lkml
Hi Daniel, On Tue, Dec 01, 2015 at 12:10:57PM -0800, Daniel Cashman wrote:
quoted hunk ↗ jump to hunk
From: dcashman <redacted> 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 <redacted> --- 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.
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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