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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 1l2G5k-0004qB-GD; Wed, 20 Jan 2021 16:12:20 +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 1l2G5g-0004nk-Cy for linux-arm-kernel@lists.infradead.org; Wed, 20 Jan 2021 16:12:18 +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 2614C31B; Wed, 20 Jan 2021 08:12:14 -0800 (PST) Received: from [10.37.8.30] (unknown [10.37.8.30]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9EE953F68F; Wed, 20 Jan 2021 08:12:12 -0800 (PST) Subject: Re: [PATCH] kasan: Add explicit preconditions to kasan_report() To: Catalin Marinas References: <20210119172607.18400-1-vincenzo.frascino@arm.com> <20210119185206.GA26948@gaia> <418db49b-1412-85ca-909e-9cdcd9fdb089@arm.com> <20210120160416.GF2642@gaia> From: Vincenzo Frascino Message-ID: <6525b31a-9258-a5d1-9188-5bce68af573c@arm.com> Date: Wed, 20 Jan 2021 16:16:02 +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: <20210120160416.GF2642@gaia> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210120_111216_531441_6AB9CEDB X-CRM114-Status: GOOD ( 26.16 ) 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 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 >>>> 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. > > 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? >> 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)); >> } > > As Andrey replied, passing a non-zero small value would still be > incorrectly detected as valid. > I would like to remove the check completely and have virt_addr_valid(addr) to return the right thing if possible. I admit, yesterday evening I did not thing it through completely before posting this code that had the sole purpose to open the discussion. I agree in principle on what Andrey said as well (addr < PAGE_SIZE). -- Regards, Vincenzo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel