[PATCH v3 1/4] mm: mmap: Add new /proc tunable for mmap_base ASLR.
From: mpe@ellerman.id.au (Michael Ellerman)
Date: 2015-11-25 04:40:06
Also in:
linux-mm, lkml
On Wed, 2015-11-18 at 15:20 -0800, Daniel Cashman wrote:
From: dcashman <redacted> ASLR currently only uses 8 bits to generate the random offset for the mmap base address on 32 bit architectures. This value was chosen to prevent a poorly chosen value from dividing the address space in such a way as to prevent large allocations. This may not be an issue on all platforms. Allow the specification of a minimum number of bits so that platforms desiring greater ASLR protection may determine where to place the trade-off.
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quoted hunk ↗ jump to hunk
diff --git a/arch/Kconfig b/arch/Kconfig index 4e949e5..141823f 100644 --- a/arch/Kconfig +++ b/arch/Kconfig@@ -511,6 +511,70 @@ config ARCH_HAS_ELF_RANDOMIZE - arch_mmap_rnd() - arch_randomize_brk() +config HAVE_ARCH_MMAP_RND_BITS + bool + help + An arch should select this symbol if it supports setting a variable + number of bits for use in establishing the base address for mmap + allocations and provides values for both: + - ARCH_MMAP_RND_BITS_MIN + - ARCH_MMAP_RND_BITS_MAX + +config ARCH_MMAP_RND_BITS_MIN + int + +config ARCH_MMAP_RND_BITS_MAX + int + +config ARCH_MMAP_RND_BITS_DEFAULT + int + +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_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
Here you support a default which is separate from the minimum.
+ default ARCH_MMAP_RND_BITS_MIN + depends on HAVE_ARCH_MMAP_RND_BITS
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+ +config ARCH_MMAP_RND_COMPAT_BITS + int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT + range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX + default ARCH_MMAP_RND_COMPAT_BITS_MIN
But here you don't. Just forgot? I'd like to have a default which is separate from the minimum. That way we can have a default which is reasonably large, but allow it to be lowered easily if anything breaks. cheers