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Message-ID: <20170220124531.GH9003@leverpostej> Date: Mon, 20 Feb 2017 12:45:32 +0000 From: Mark Rutland <mark.rutland@....com> To: Ard Biesheuvel <ard.biesheuvel@...aro.org> Cc: Hoeun Ryu <hoeun.ryu@...il.com>, Kees Cook <keescook@...omium.org>, kernel-hardening@...ts.openwall.com, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Laura Abbott <labbott@...hat.com>, Kefeng Wang <wangkefeng.wang@...wei.com>, Jeremy Linton <jeremy.linton@....com>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org> Subject: Re: [RFC 7/7] arm64: map seperately rodata sections for __ro_mostly_after_init section On Sun, Feb 19, 2017 at 11:35:51AM +0000, Ard Biesheuvel wrote: > On 19 February 2017 at 10:04, Hoeun Ryu <hoeun.ryu@...il.com> wrote: > > Map rodata sections seperately for the new __ro_mostly_after_init section. > > Attribute of memory for __ro_mostly_after_init section can be changed later > > so we need a dedicated vmalloced region for set_memory_rw/ro api. > While it is correct that you are splitting this into three separate > segments (otherwise we would not be able to change the permissions > later without risking splitting to occur), I think this leads to > unnecessary fragmentation. > > If there is demand for this feature (but you still need to make the > argument for that), I wonder if it wouldn't be sufficient, and much > more straightforward, to redefine the __ro_after_init semantics to > include the kind of subsystem registration and module init context you > are targeting, and implement some hooks to temporarily lift the > __ro_after_init r/o permission restrictions in a controlled manner. >From a look over the series, I think this is just __write_rarely in disguise. I personally think that we should keep __write_rarely and __ro_after_init separate, the later being a strictly one-shot affair. I had some ideas [1] as to how we could implement __write_rarely without carving up the kernel mapping further (and keeping the RW permissions local to the thread needing it), but I have not had the time to look into that further. Thanks, Mark. [1] http://www.openwall.com/lists/kernel-hardening/2016/11/18/3
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