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Message-ID: <CACi5LpNyyc6GPF67EwD9rQ_djyewwh8t5tHperE6Ka70B6g+iw@mail.gmail.com> 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 [1]). However as Kees noted in one of his reviews, I think this 2nd patch might not be needed for all generic ppc platforms. [1] http://lxr.free-electrons.com/source/arch/powerpc/include/asm/elf.h#L26. Regards, Bhupesh
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