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

[Alexander Potapenko <glider@google.com>]

> +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)