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Tue, 19 Jan 2021 19:02:30 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1l1wGm-0001AJ-SS for linux-arm-kernel@lists.infradead.org; Tue, 19 Jan 2021 19:02:28 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 547DD20706; Tue, 19 Jan 2021 19:02:22 +0000 (UTC) Date: Tue, 19 Jan 2021 19:02:19 +0000 From: Catalin Marinas To: Vincenzo Frascino Subject: Re: [PATCH] kasan: Add explicit preconditions to kasan_report() Message-ID: <20210119190219.GC26948@gaia> References: <20210119172607.18400-1-vincenzo.frascino@arm.com> <20210119185206.GA26948@gaia> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210119_140225_061984_FBC10C05 X-CRM114-Status: GOOD ( 27.86 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Andrey Konovalov , LKML , kasan-dev , Leon Romanovsky , Alexander Potapenko , Dmitry Vyukov , Andrey Ryabinin , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 > >> 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 > >>> Cc: Alexander Potapenko > >>> Cc: Dmitry Vyukov > >>> Cc: Leon Romanovsky > >>> Cc: Andrey Konovalov > >>> Signed-off-by: Vincenzo Frascino > >>> --- > >>> 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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel