Date: Fri, 26 Aug 2016 09:08:01 -0600 From: Warner Losh <imp@bsdimp.com> To: Pedro Giffuni <pfg@freebsd.org> Cc: Ed Maste <emaste@freebsd.org>, "freebsd-toolchain@FreeBSD.org" <freebsd-toolchain@freebsd.org> Subject: Re: Time to enable partial relro Message-ID: <CANCZdfpQbAe8pnxZuCab0JoW5ByGbVbKtEJjrBmL=-kMdg_PnA@mail.gmail.com> In-Reply-To: <6af6f640-a00a-1359-d40f-c62b40eafb9c@FreeBSD.org> References: <b75890eb-d8bd-759e-002f-ab0c16db0975@FreeBSD.org> <CANCZdfqAmhN1owbo_rDt5xjC%2BbboOHrgu2xDHeZi1P02rX7EwQ@mail.gmail.com> <CAPyFy2B3j7h9Cme=8VPs4ogOMgYAWvbyggZ3NMJraz5xoWqiXg@mail.gmail.com> <CANCZdfp9Roc=MyrD8UO-efKOn5vSsOprM9juw6NeYT2T0Ag0wg@mail.gmail.com> <6af6f640-a00a-1359-d40f-c62b40eafb9c@FreeBSD.org>
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On Fri, Aug 26, 2016 at 9:06 AM, Pedro Giffuni <pfg@freebsd.org> wrote: > > > On 08/26/16 10:01, Warner Losh wrote: >> >> On Fri, Aug 26, 2016 at 8:36 AM, Ed Maste <emaste@freebsd.org> wrote: >>> >>> On 26 August 2016 at 10:18, Warner Losh <imp@bsdimp.com> wrote: >>>> >>>> >>>> So what's the summary of why we'd want to do that? What benefit does it >>>> bring? >>>> Sure, other folks do it, but why? >>> >>> >>> It's a relatively low cost technique to mitigate certain >>> vulnerabilities. rtld needs to write to some sections during load but >>> they don't need to be writeable after starting the program. relro >>> reorders the output sections so that they are grouped together, and >>> rtld remaps them read-only on start. This is often called "partial >>> relro." I don't know of any real downside to enabling it, other than >>> it could possibly break some strangely built third party software. >>> It's been enabled on other platforms for quite some time though and I >>> doubt we'd run into new issues. >>> >>> It doesn't bring a huge benefit by itself though; the PLT is still >>> writeable. Adding "-z now" to the linker invocation produces "full >>> relro" which makes the PLT read-only too. It has a negative impact on >>> process start-up time though. >> >> >> Sounds like this has implications for all the RTLD on all our >> architectures. Has this been tested across all of them? >> > > It affects anything ELF yes, but AFAICT the change is platform independent. That's a different answer than 'it's been tested on all platforms and it's fine.' Warner
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