linux-kernel - Re: [PATCH 10/11] kasan: fix bug detection via ksize for HW

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Date:   Tue, 12 Jan 2021 23:54:43 +0100
From:   Marco Elver <elver@...gle.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Will Deacon <will.deacon@....com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/11] kasan: fix bug detection via ksize for HW_TAGS mode

On Tue, 12 Jan 2021 at 22:16, Andrey Konovalov <andreyknvl@...gle.com> wrote:
>
> On Tue, Jan 12, 2021 at 3:32 PM Marco Elver <elver@...gle.com> wrote:
> >
> > > +/*
> > > + * Unlike kasan_check_read/write(), kasan_check_byte() is performed even for
> > > + * the hardware tag-based mode that doesn't rely on compiler instrumentation.
> > > + */
> >
> > We have too many check-functions, and the name needs to be more precise.
> > Intuitively, I would have thought this should have access-type, i.e.
> > read or write, effectively mirroring a normal access.
> >
> > Would kasan_check_byte_read() be better (and just not have a 'write'
> > variant because we do not need it)? This would restore ksize() closest
> > to what it was before (assuming reporting behaviour is fixed, too).
>
> > >  void kasan_poison(const void *address, size_t size, u8 value);
> > >  void kasan_unpoison(const void *address, size_t size);
> > > -bool kasan_check_invalid_free(void *addr);
> > > +bool kasan_check(const void *addr);
> >
> > Definitely prefer shorted names, but we're in the unfortunate situation
> > of having numerous kasan_check-functions, so we probably need to be more
> > precise.
> >
> > kasan_check() makes me think this also does reporting, but it does not
> > (it seems to only check the metadata for validity).
> >
> > The internal function could therefore be kasan_check_allocated() (it's
> > now the inverse of kasan_check_invalid_free()).
>
> Re: kasan_check_byte():
>
> I think the _read suffix is only making the name longer. ksize() isn't
> checking that the memory is readable (or writable), it's checking that
> it's addressable. At least that's the intention of the annotation, so
> it makes sense to name it correspondingly despite the implementation.
>
> Having all kasan_check_*() functions both checking and reporting makes
> sense, so let's keep the kasan_check_ prefix.
>
> What isn't obvious from the name is that this function is present for
> every kasan mode. Maybe kasan_check_byte_always()? Although it also
> seems too long.
>
> But I'm OK with keeping kasan_check_byte().

This is fine.

> Re kasan_check():
>
> Here we can use Andrew's suggestion about the name being related to
> what the function returns. And also drop the kasan_check_ prefix as
> this function only does the checking.
>
> Let's use kasan_byte_accessible() instead of kasan_check().

Sounds reasonable to me.

Thanks,
-- Marco