Messages in this thread | | | Subject | Re: [PATCH] kasan: Add explicit preconditions to kasan_report() | From | Vincenzo Frascino <> | Date | Tue, 19 Jan 2021 20:35:49 +0000 |
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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.frascino@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 <aryabinin@virtuozzo.com> >>> Cc: Alexander Potapenko <glider@google.com> >>> Cc: Dmitry Vyukov <dvyukov@google.com> >>> Cc: Leon Romanovsky <leonro@mellanox.com> >>> Cc: Andrey Konovalov <andreyknvl@google.com> >>> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@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.
An option could be to make an exception for virtual address 0 in addr_has_metadata() something like:
static inline bool addr_has_metadata(const void *addr) { if ((u64)addr == 0) return false;
return (is_vmalloc_addr(addr) || virt_addr_valid(addr)); }
Let me know what do you think.
Thanks! -- Regards, Vincenzo
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