Date: Thu, 2 Feb 2017 23:51:49 +0530 From: Bhupesh Sharma <bhsharma@...hat.com> To: Balbir Singh <bsingharora@...il.com> Cc: linuxppc-dev@...ts.ozlabs.org, kernel-hardening@...ts.openwall.com, Alistair Popple <alistair@...ple.id.au>, Anatolij Gustschin <agust@...x.de>, Kees Cook <keescook@...omium.org>, Daniel Cashman <dcashman@...roid.com>, Scott Wood <oss@...error.net>, Paul Mackerras <paulus@...ba.org>, Daniel Cashman <dcashman@...gle.com>, Bhupesh SHARMA <bhupesh.linux@...il.com>, Alexander Graf <agraf@...e.com> Subject: Re: [PATCH 0/2] RFC: Adjust powerpc ASLR elf randomness Hi Balbir, On Thu, Feb 2, 2017 at 12:14 PM, Balbir Singh <bsingharora@...il.com> wrote: > On Thu, Feb 02, 2017 at 11:12:46AM +0530, Bhupesh Sharma wrote: >> This RFC patchset tries to make the powerpc ASLR elf randomness >> implementation similar to other ARCHs (like x86). >> >> The 1st patch introduces the support of ARCH_MMAP_RND_BITS in powerpc >> mmap implementation to allow a sane balance between increased randomness >> in the mmap address of ASLR elfs and increased address space >> fragmentation. >> > > From what I see we get 28 bits of entropy right for 64k pages > bits as compared to 14 bits earlier? That's correct. We can go upto 28-bits of entropy for 64BIT platforms using 64K pages with the current approach. I see arm64 using > 28 bits of entropy randomness in some cases, but I think 28-bit MAX entropy is sensible for 64BIT/64K combination on PPC. >> The 2nd patch increases the ELF_ET_DYN_BASE value from the current >> hardcoded value of 0x2000_0000 to something more practical, >> i.e. TASK_SIZE - PAGE_SHIFT (which makes sense especially for >> 64-bit platforms which would like to utilize more randomization >> in the load address of a PIE elf). >> > > This helps PIE executables as such and leaves other not impacted? It basically affects all shared object files (as noted in ). However as Kees noted in one of his reviews, I think this 2nd patch might not be needed for all generic ppc platforms.  http://lxr.free-electrons.com/source/arch/powerpc/include/asm/elf.h#L26. Regards, Bhupesh
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