On Wed, Jan 20, 2021 at 04:16:02PM +0000, Vincenzo Frascino wrote: > On 1/20/21 4:04 PM, Catalin Marinas wrote: > > On Tue, Jan 19, 2021 at 08:35:49PM +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)); > >>> > >> > >> This seems not working on arm64 because according to virt_addr_valid 0 is a > >> valid virtual address, in fact: > >> > >> __is_lm_address(0) == true && pfn_valid(virt_to_pfn(0)) == true. > > > > Ah, so __is_lm_address(0) is true. Maybe we should improve this since > > virt_to_pfn(0) doesn't make much sense. > > How do you propose to improve it?
Check that it's actually a kernel address starting at PAGE_OFFSET. The current __is_lm_address() check just masks out the top 12 bits but if they were 0, this still yields a true result. Maybe extending the current definition as: #define __is_lm_address(addr) ((u64)(addr) >= PAGE_OFFSET && \ ((u64)(addr) & ~PAGE_OFFSET) < (PAGE_END - PAGE_OFFSET)) Which basically means: #define __is_lm_address(addr) ((u64)(addr) >= PAGE_OFFSET && \ (u64)(addr) < PAGE_END) I think we could write the above as: #define __is_lm_address(addr) (((u64)(addr) ^ PAGE_OFFSET) < (PAGE_END - PAGE_OFFSET)) This way we catch any 0 bits in the top 12 (or 16 with a 48-bit VA configuration). -- Catalin