linux-kernel - Re: [PATCH v2 0/4] kasan, arm64, scs, stacktrace: collect stack traces from Shadow Call Stack

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Message-ID: <CA+fCnZcPOfBuOMiXsaQzWMYxG=L_QGVgLDAdNWmYciA0JT+Deg@mail.gmail.com>
Date:   Tue, 29 Mar 2022 22:11:45 +0200
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Marco Elver <elver@...gle.com>
Cc:     andrey.konovalov@...ux.dev,
        Alexander Potapenko <glider@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Mark Rutland <mark.rutland@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Florian Mayer <fmayer@...gle.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH v2 0/4] kasan, arm64, scs, stacktrace: collect stack
 traces from Shadow Call Stack

On Tue, Mar 29, 2022 at 8:36 PM Andrey Konovalov <andreyknvl@...il.com> wrote:
>
> On Mon, Mar 28, 2022 at 2:36 PM Marco Elver <elver@...gle.com> wrote:
> >
> > > Changes v1->v2:
> > > - Provide a kernel-wide stack_trace_save_shadow() interface for collecting
> > >   stack traces from shadow stack.
> > > - Use ptrauth_strip_insn_pac() and READ_ONCE_NOCHECK, see the comments.
> > > - Get SCS pointer from x18, as per-task value is meant to save the SCS
> > >   value on CPU switches.
> > > - Collect stack frames from SDEI and IRQ contexts.
> >
> > Do any of these new changes introduce new (noticeable) overhead (in
> > particular patch 2)?
>
> I'll measure the overheads and include the results into v3. Thanks!

Hm, looks like the overhead is overly significant: ~5%. I'll explore a
different approach in v3 instead.