On Tue, Jan 19, 2021 at 07:00:57PM +0000, Vincenzo Frascino wrote: > On 1/19/21 6:52 PM, Catalin Marinas wrote: > > 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)); > > Or we could have both ;)
True. Documentation doesn't hurt (well, only when it's wrong ;)). -- Catalin
