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Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1l1xfY-0000De-Vl; Tue, 19 Jan 2021 20:32:05 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1l1xfW-0000DH-Fm for linux-arm-kernel@lists.infradead.org; Tue, 19 Jan 2021 20:32:03 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A0FDAD6E; Tue, 19 Jan 2021 12:32:01 -0800 (PST) Received: from [10.37.8.29] (unknown [10.37.8.29]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 24D853F719; Tue, 19 Jan 2021 12:32:00 -0800 (PST) Subject: Re: [PATCH] kasan: Add explicit preconditions to kasan_report() To: Catalin Marinas , Andrey Konovalov References: <20210119172607.18400-1-vincenzo.frascino@arm.com> <20210119185206.GA26948@gaia> From: Vincenzo Frascino Message-ID: <418db49b-1412-85ca-909e-9cdcd9fdb089@arm.com> Date: Tue, 19 Jan 2021 20:35:49 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210119185206.GA26948@gaia> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210119_153202_622311_E2C3E06A X-CRM114-Status: GOOD ( 25.22 ) 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: 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 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)); > 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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel