On Tue, Jan 19, 2021 at 07:27:43PM +0100, Andrey Konovalov wrote: > On Tue, Jan 19, 2021 at 6:26 PM Vincenzo Frascino > <vincenzo.frasc...@arm.com> wrote: > > > > With the introduction of KASAN_HW_TAGS, kasan_report() dereferences > > the address passed as a parameter. > > > > Add a comment to make sure that the preconditions to the function are > > explicitly clarified. > > > > Note: An invalid address (e.g. NULL pointer address) passed to the > > function when, KASAN_HW_TAGS is enabled, leads to a kernel panic. > > > > Cc: Andrey Ryabinin <aryabi...@virtuozzo.com> > > Cc: Alexander Potapenko <gli...@google.com> > > Cc: Dmitry Vyukov <dvyu...@google.com> > > Cc: Leon Romanovsky <leo...@mellanox.com> > > Cc: Andrey Konovalov <andreyk...@google.com> > > Signed-off-by: Vincenzo Frascino <vincenzo.frasc...@arm.com> > > --- > > mm/kasan/report.c | 11 +++++++++++ > > 1 file changed, 11 insertions(+) > > > > diff --git a/mm/kasan/report.c b/mm/kasan/report.c > > index c0fb21797550..2485b585004d 100644 > > --- a/mm/kasan/report.c > > +++ b/mm/kasan/report.c > > @@ -403,6 +403,17 @@ static void __kasan_report(unsigned long addr, size_t > > size, bool is_write, > > end_report(&flags); > > } > > > > +/** > > + * kasan_report - report kasan fault details > > + * @addr: valid address of the allocation where the tag fault was detected > > + * @size: size of the allocation where the tag fault was detected > > + * @is_write: the instruction that caused the fault was a read or write? > > + * @ip: pointer to the instruction that cause the fault > > + * > > + * Note: When CONFIG_KASAN_HW_TAGS is enabled kasan_report() dereferences > > + * the address to access the tags, hence it must be valid at this point in > > + * order to not cause a kernel panic. > > + */ > > It doesn't dereference the address, it just checks the tags, right? > > Ideally, kasan_report() should survive that with HW_TAGS like with the > other modes. The reason it doesn't is probably because of a blank > addr_has_metadata() definition for HW_TAGS in mm/kasan/kasan.h. I > guess we should somehow check that the memory comes from page_alloc or > kmalloc. Or otherwise make sure that it has tags. Maybe there's an arm > instruction to check whether the memory has tags?
There isn't an architected way to probe whether a memory location has a VA->PA mapping. The tags are addressed by PA but you can't reach them if you get a page fault on the VA. So we either document the kasan_report() preconditions or, as you suggest, update addr_has_metadata() for the HW_TAGS case. Something like: return is_vmalloc_addr(virt) || virt_addr_valid(virt)); -- Catalin