Date: Wed, 23 Jul 2014 17:45:51 -0700 From: Tim Kientzle <tim@kientzle.com> To: Pedro Giffuni <pfg@freebsd.org> Cc: Shawn Webb <lattera@gmail.com>, Oliver Pinter <oliver.pntr@gmail.com>, Robert Watson <rwatson@freebsd.org>, freebsd-arch@freebsd.org, PaX Team <pageexec@freemail.hu>, Bryan Drewery <bdrewery@freebsd.org> Subject: Re: [RFC] ASLR Whitepaper and Candidate Final Patch Message-ID: <796EDB88-3768-48AA-B909-8A7FFBED0C1E@kientzle.com> In-Reply-To: <D7CEDB47-2818-461A-BB70-479BEBDCEEE9@freebsd.org> References: <96C72773-3239-427E-A90B-D05FF0F5B782@freebsd.org> <20140720201858.GB29618@pwnie.vrt.sourcefire.com> <alpine.BSF.2.11.1407230017490.88645@fledge.watson.org> <20140723004543.GH29618@pwnie.vrt.sourcefire.com> <D7CEDB47-2818-461A-BB70-479BEBDCEEE9@freebsd.org>
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On Jul 23, 2014, at 4:37 PM, Pedro Giffuni <pfg@freebsd.org> wrote: > Hi; >=20 > Il giorno 22/lug/2014, alle ore 19:45, Shawn Webb <lattera@gmail.com> = ha scritto: >=20 >>>> ... >>>=20 >>> Hi Shawn: >>>=20 >>> Great news that this work is coming to fruition -- ASLR is long = overdue. >>>=20 >>> Are you having any luck with performance measurements? Unixbench = seems like a=20 >>> good starting point, but I wonder if it would be useful to look, in=20= >>> particular, at memory-mapping intensive workloads that might be = affected as a=20 >>> result of changes in kernel VM data-structure use, or greater = fragmentation of=20 >>> the address space. I'm not sure I have a specific application here = in mind --=20 >>> in the past I might have pointed out tools such as ElectricFence = that tend to=20 >>> increase fragmentation themselves. >>=20 >> The unixbench tests on that laptop have finished. However, I've been >> fighting a pesky migraine these last couple days, so I haven't had = the >> opportunity to aggregate the results into a nice little spreadsheet. = I'm >> hoping to finish it up by the end of the week. >>=20 >> I'll take a look at ElectricFence this weekend. Additionally, I have = a >> netbook somewhere. Once I find it and its power cord, I'll install >> FreeBSD/x86 and re-run the same tests on that. >>=20 >=20 > Somewhat related to ElectricFence=85 will ASLR have an adverse effect = on debuggers? >=20 > I googled around and got to this: >=20 > http://www.outflux.net/blog/archives/2010/07/03/gdb-turns-off-aslr/ >=20 > So I guess we may have to patch gdb (and lldb)? I suspect the issue here is that debugging often requires multiple runs of a program with repeatable behavior between runs. Consider: * I run the program under GDB, it crashes at a certain PC address * I restart the program, set a breakpoint at that PC address I want to be confident that the PC address where I=92m setting the breakpoint will have the same meaning between runs. Tim
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