Re: [PATCH 2/2] lib/test_kasan: Add stack overflow test

[Marco Elver]

On Tue, 23 Jul 2019 at 18:24, Mark Rutland <mark.rutland@xxxxxxx> wrote:
>
> On Fri, Jul 19, 2019 at 03:28:18PM +0200, Marco Elver wrote:
> > Adds a simple stack overflow test, to check the error being reported on
> > an overflow. Without CONFIG_STACK_GUARD_PAGE, the result is typically
> > some seemingly unrelated KASAN error message due to accessing random
> > other memory.
>
> Can't we use the LKDTM_EXHAUST_STACK case to check this?
>
> I was also under the impression that the other KASAN self-tests weren't
> fatal, and IIUC this will kill the kernel.
>
> Given that, and given this is testing non-KASAN functionality, I'm not
> sure it makes sense to bundle this with the KASAN tests.

Thanks for pointing out LKDTM_EXHAUST_STACK.

This patch can be dropped!

-- Marco

> Thanks,
> Mark.
>
> >
> > Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Borislav Petkov <bp@xxxxxxxxx>
> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> > Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> > Cc: Alexander Potapenko <glider@xxxxxxxxxx>
> > Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> > Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: x86@xxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > Cc: kasan-dev@xxxxxxxxxxxxxxxx
> > ---
> >  lib/test_kasan.c | 36 ++++++++++++++++++++++++++++++++++++
> >  1 file changed, 36 insertions(+)
> >
> > diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> > index b63b367a94e8..3092ec01189d 100644
> > --- a/lib/test_kasan.c
> > +++ b/lib/test_kasan.c
> > @@ -15,6 +15,7 @@
> >  #include <linux/mman.h>
> >  #include <linux/module.h>
> >  #include <linux/printk.h>
> > +#include <linux/sched/task_stack.h>
> >  #include <linux/slab.h>
> >  #include <linux/string.h>
> >  #include <linux/uaccess.h>
> > @@ -709,6 +710,32 @@ static noinline void __init kmalloc_double_kzfree(void)
> >       kzfree(ptr);
> >  }
> >
> > +#ifdef CONFIG_STACK_GUARD_PAGE
> > +static noinline void __init stack_overflow_via_recursion(void)
> > +{
> > +     volatile int n = 512;
> > +
> > +     BUILD_BUG_ON(IS_ENABLED(CONFIG_STACK_GROWSUP));
> > +
> > +     /* About to overflow: overflow via alloca'd array and try to write. */
> > +     if (!object_is_on_stack((void *)&n - n)) {
> > +             volatile char overflow[n];
> > +
> > +             overflow[0] = overflow[0];
> > +             return;
> > +     }
> > +
> > +     stack_overflow_via_recursion();
> > +}
> > +
> > +static noinline void __init kasan_stack_overflow(void)
> > +{
> > +     pr_info("stack overflow begin\n");
> > +     stack_overflow_via_recursion();
> > +     pr_info("stack overflow end\n");
> > +}
> > +#endif
> > +
> >  static int __init kmalloc_tests_init(void)
> >  {
> >       /*
> > @@ -753,6 +780,15 @@ static int __init kmalloc_tests_init(void)
> >       kasan_bitops();
> >       kmalloc_double_kzfree();
> >
> > +#ifdef CONFIG_STACK_GUARD_PAGE
> > +     /*
> > +      * Only test with CONFIG_STACK_GUARD_PAGE, as without we get other
> > +      * random KASAN violations, due to accessing other random memory (we
> > +      * want to avoid actually corrupting memory in these tests).
> > +      */
> > +     kasan_stack_overflow();
> > +#endif
> > +
> >       kasan_restore_multi_shot(multishot);
> >
> >       return -EAGAIN;
> > --
> > 2.22.0.657.g960e92d24f-goog
> >
>
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