linux-kernel - Re: [PATCH] kasan: add support for kasan.fault=panic_on

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Date:   Tue, 20 Jun 2023 13:32:57 +0200
From:   Marco Elver <elver@...gle.com>
To:     Andrey Konovalov <andreyknvl@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Taras Madan <tarasmadan@...gle.com>,
        Aleksandr Nogikh <nogikh@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Jonathan Corbet <corbet@....net>, kasan-dev@...glegroups.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH] kasan: add support for kasan.fault=panic_on_write

On Tue, 20 Jun 2023 at 12:57, Andrey Konovalov <andreyknvl@...il.com> wrote:
>
> On Wed, Jun 14, 2023 at 11:52 AM Marco Elver <elver@...gle.com> wrote:
> >
> > @@ -597,7 +614,11 @@ void kasan_report_async(void)
> >         pr_err("Asynchronous fault: no details available\n");
> >         pr_err("\n");
> >         dump_stack_lvl(KERN_ERR);
> > -       end_report(&flags, NULL);
> > +       /*
> > +        * Conservatively set is_write=true, because no details are available.
> > +        * In this mode, kasan.fault=panic_on_write is like kasan.fault=panic.
> > +        */
> > +       end_report(&flags, NULL, true);
>
> Hi Marco,
>
> When asymm mode is enabled, kasan_report_async should only be called
> for read accesses. I think we could check the mode and panic
> accordingly.

How do we check the mode, and how do we prove it's only called for
read accesses?

> Please also update the documentation to describe the flag behavior wrt
> async/asymm modes.

Will do.

> On a related note, it looks like we have a typo in KASAN
> documentation: it states that asymm mode detects reads synchronously,
> and writes - asynchronously. Should be the reverse.

This says the documentation is correct, and it's actually called for
writes: https://docs.kernel.org/arm64/memory-tagging-extension.html#tag-check-faults

Who is right?