linux-kernel - Re: [PATCH v2 13/48] kmsan: add KMSAN runtime core

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Message-ID: <CAG_fn=XvC7UPaBbcDM4-Rc_4RdWSceQK5jV9n6q7DtTeZbd0zw@mail.gmail.com>
Date:   Mon, 4 Apr 2022 16:39:31 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Christoph Hellwig <hch@....de>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kees Cook <keescook@...omium.org>,
        Marco Elver <elver@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Matthew Wilcox <willy@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 13/48] kmsan: add KMSAN runtime core

> +depot_stack_handle_t kmsan_save_stack_with_flags(gfp_t flags,
> +                                                unsigned int extra)
> +{
> +       unsigned long entries[KMSAN_STACK_DEPTH];
> +       unsigned int nr_entries;
> +
> +       nr_entries = stack_trace_save(entries, KMSAN_STACK_DEPTH, 0);
> +       nr_entries = filter_irq_stacks(entries, nr_entries);

This is redundant, __stack_depot_save() below already calls filter_irq_stacks().

> +
> +       if (depth >= MAX_CHAIN_DEPTH) {
> +               static atomic_long_t kmsan_skipped_origins;
> +               long skipped = atomic_long_inc_return(&kmsan_skipped_origins);
> +
> +               if (skipped % NUM_SKIPPED_TO_WARN == 0) {
> +                       pr_warn("not chained %ld origins\n", skipped);
> +                       dump_stack();
> +                       kmsan_print_origin(id);
> +               }
> +               return id;
> +       }
> +       depth++;
> +       extra_bits = kmsan_extra_bits(depth, uaf);
> +
> +       entries[0] = KMSAN_CHAIN_MAGIC_ORIGIN;
> +       entries[1] = kmsan_save_stack_with_flags(GFP_ATOMIC, 0);
> +       entries[2] = id;
> +       return __stack_depot_save(entries, ARRAY_SIZE(entries), extra_bits,
> +                                 GFP_ATOMIC, true);

@entries is initialized in non-instrumented code, so passing it to
filter_irq_stacks() etc. will result in false positives, unless we
explicitly unpoison it.
(right now KMSAN does not instrument kernel/stacktrace.c, but it
probably should)