Re: [PATCH v2] mm: Make ksize() a reporting-only function

[Andrey Konovalov]

On Sun, Nov 27, 2022 at 1:55 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> > I just realized there's an issue here with the tag-based modes, as
> > they align the unpoisoned area to 16 bytes.
> >
> > One solution would be to change the allocation size to 128 -
> > KASAN_GRANULE_SIZE - 5, the same way kmalloc_oob_right test does it,
> > so that the last 16-byte granule won't get unpoisoned for the
> > tag-based modes. And then check that the ptr[size] access fails only
> > for the Generic mode.
>
> Ah! Good point. Are you able to send a patch? I suspect you know exactly
> what to change; it might take me a bit longer to double-check all of
> those details.

Let's do it like this:

size_t size = 128 - KASAN_GRANULE_SIZE - 5, real_size.

...

/* These must trigger a KASAN report. */
if (IS_ENABLED(CONFIG_KASAN_GENERIC))
    KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[size]);
KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[size + 5]);
KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[real_size - 1]);

Thanks!