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Date: Tue, 6 Oct 2015 10:38:20 +0300 From: Andrey Ryabinin <aryabinin@...tuozzo.com> To: Ingo Molnar <mingo@...nel.org> CC: Andi Kleen <ak@...ux.intel.com>, Dmitry Vyukov <dvyukov@...gle.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>, Andy Lutomirski <luto@...capital.net>, Andrey Konovalov <andreyknvl@...gle.com>, Kostya Serebryany <kcc@...gle.com>, Alexander Potapenko <glider@...gle.com>, kasan-dev <kasan-dev@...glegroups.com>, Borislav Petkov <bp@...en8.de>, Denys Vlasenko <dvlasenk@...hat.com>, Sasha Levin <sasha.levin@...cle.com>, Wolfram Gloger <wmglo@...t.med.uni-muenchen.de>, Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [PATCH] x86/process: Silence KASAN warnings in get_wchan() On 10/06/2015 10:26 AM, Ingo Molnar wrote: > > * Andrey Ryabinin <aryabinin@...tuozzo.com> wrote: > >> On 10/05/2015 07:39 PM, Andi Kleen wrote: >>>> But, I think I have the solution. >>>> We could have some blacklist - list of function names which we should be ignored. >>>> In kasan_report() we could resolve return address to function name and compare it with name in list. >>>> If name in list -> ignore report. >>> >>> I think annotating statements is cleaner than functions, even if it >>> is more code. Much better documentation >>> >> >> I agree with that, that's why I suggested to add READ_ONCE_NOCHECK(): >> READ_ONCE_NOCHECK() >> { >> kasan_disable_current(); >> READ_ONCE(); >> kasan_enable_current(); >> } >> >> Anywone objects? > > Sounds good to me! As long as it's hidden from plain .c files I'm a happy camper. > > This should probably also be faster for KASAN than triggering a warning and having > to parse a blacklist, right? > Sure. >>> If disabling with an attribute doesn't work, you could put it into a special >>> section with __attribute__((section ...)) and check the start/end symbol >>> before reporting. That's how kprobes solves similar issues. It also has the >>> advantage that it stops inlining. >> >> Yes, it might be better. Although, because of broken -fconserve-stack, this may >> not work in some cases - https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533 >> Function splitter may split original function into two parts and it always puts >> one split part in default .text section. > > We do a _ton_ of such section tricks in the kernel (all of exception handling is > based on that) - if that's broken by -fconserve-stack then the kernel is broken > much more widely. > I'm mistaken here. It was broken once, at some point of development of gcc 5, but this was fixed eventually. I just checked gcc 5.2, 4.9.2, 4.8.4, all of them are ok. > So unless KASAN wants to do something special here you can rely on sections just > fine. > > Thanks, > > Ingo > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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