Messages in this thread | | | Date | Wed, 7 Oct 2015 09:22:37 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86/process: Silence KASAN warnings in get_wchan() |
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* Andy Lutomirski <luto@amacapital.net> wrote:
> On Tue, Oct 6, 2015 at 12:26 AM, Ingo Molnar <mingo@kernel.org> wrote: > > > > * Andrey Ryabinin <aryabinin@virtuozzo.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? > > > >> > 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. > > > > So unless KASAN wants to do something special here you can rely on sections just > > fine. > > Kprobes is moving away from a section approach for some reason (not > sure why), but the kprobe approach should work, too.
Do you mean NOKPROBE_SYMBOL() vs __kprobes?
So one concern is with functions being in multiple blacklists, so yeah, the NOKPROBE_SYMBOL() approach might be more robust than __kprobes.
But note that NOKPROBE_SYMBOL() itself is still section based:
#define __NOKPROBE_SYMBOL(fname) \ static unsigned long __used \ __attribute__((section("_kprobe_blacklist"))) \ _kbl_addr_##fname = (unsigned long)fname;
Thanks,
Ingo
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