From: Marco Elver <elver@google.com>
To: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Alexander Potapenko <glider@google.com>,
Dmitry Vyukov <dvyukov@google.com>,
Taras Madan <tarasmadan@google.com>,
Aleksandr Nogikh <nogikh@google.com>,
Andrey Ryabinin <ryabinin.a.a@gmail.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Jonathan Corbet <corbet@lwn.net>,
kasan-dev@googlegroups.com, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Catalin Marinas <catalin.marinas@arm.com>
Subject: Re: [PATCH] kasan: add support for kasan.fault=panic_on_write
Date: Tue, 20 Jun 2023 13:51:05 +0200 [thread overview]
Message-ID: <ZJGSqdDQPs0sRQTb@elver.google.com> (raw)
In-Reply-To: <CA+fCnZccdLNqtxubVVtGPTOXcSoYfpM9CHk-nrYsZK7csC77Eg@mail.gmail.com>
On Tue, Jun 20, 2023 at 01:45PM +0200, Andrey Konovalov wrote:
> On Tue, Jun 20, 2023 at 1:33 PM Marco Elver <elver@google.com> wrote:
> >
> > > 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?
>
> Ah, right. I did a quick google to check when I was writing the
> response and found this: https://lwn.net/Articles/882963/. But looks
> like that cover letter is wrong and the documentation is right. I
> wonder what the point of the asymmetric mode is then.
Maybe not as strong, but asymm mode makes sense from a microarch point
of view, where writes are always committed into a store buffer, but
reads can only commit when the data (incl. tag) is available.
> So the current code that you have should work perfectly. The only
> change I'd like to see is in the documentation.
Something like this (or more?)
diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index 7f37a46af574..3c58392d931e 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -135,6 +135,8 @@ disabling KASAN altogether or controlling its features:
fault occurs, the information is stored in hardware (in the TFSR_EL1
register for arm64). The kernel periodically checks the hardware and
only reports tag faults during these checks.
+ Note that ``kasan.fault=panic_on_write`` results in panic for all
+ asynchronously checked accesses.
Asymmetric mode: a bad access is detected synchronously on reads and
asynchronously on writes.
next prev parent reply other threads:[~2023-06-20 11:51 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-14 9:51 [PATCH] kasan: add support for kasan.fault=panic_on_write Marco Elver
2023-06-14 10:06 ` Alexander Potapenko
2023-06-20 10:57 ` Andrey Konovalov
2023-06-20 11:32 ` Marco Elver
2023-06-20 11:45 ` Andrey Konovalov
2023-06-20 11:51 ` Marco Elver [this message]
2023-06-20 13:56 ` Andrey Konovalov
2023-06-20 14:48 ` Marco Elver
2023-06-20 16:27 ` Andrey Konovalov
2023-06-20 17:17 ` [PATCH] kasan, doc: note kasan.fault=panic_on_write behaviour for async modes Marco Elver
2023-06-20 17:19 ` Andrey Konovalov
2023-06-20 17:23 ` [PATCH] kasan: add support for kasan.fault=panic_on_write Marco Elver
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