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[2001:44b8:1113:6700:783a:2bb9:f7cb:7c3c]) by smtp.gmail.com with ESMTPSA id q6sm75232pgn.44.2019.10.30.07.21.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Oct 2019 07:21:17 -0700 (PDT) From: Daniel Axtens To: Andrey Ryabinin , kasan-dev@googlegroups.com, linux-mm@kvack.org, x86@kernel.org, glider@google.com, luto@kernel.org, linux-kernel@vger.kernel.org, mark.rutland@arm.com, dvyukov@google.com, christophe.leroy@c-s.fr Cc: linuxppc-dev@lists.ozlabs.org, gor@linux.ibm.com, Andrew Morton Subject: Re: [PATCH v10 4/5] x86/kasan: support KASAN_VMALLOC In-Reply-To: References: <20191029042059.28541-1-dja@axtens.net> <20191029042059.28541-5-dja@axtens.net> <87sgnamjg2.fsf@dja-thinkpad.axtens.net> Date: Thu, 31 Oct 2019 01:21:13 +1100 Message-ID: <87mudimi06.fsf@dja-thinkpad.axtens.net> MIME-Version: 1.0 Content-Type: text/plain X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Andrey Ryabinin writes: > On 10/30/19 4:50 PM, Daniel Axtens wrote: >> Andrey Ryabinin writes: >> >>> On 10/29/19 7:20 AM, Daniel Axtens wrote: >>>> In the case where KASAN directly allocates memory to back vmalloc >>>> space, don't map the early shadow page over it. >>>> >>>> We prepopulate pgds/p4ds for the range that would otherwise be empty. >>>> This is required to get it synced to hardware on boot, allowing the >>>> lower levels of the page tables to be filled dynamically. >>>> >>>> Acked-by: Dmitry Vyukov >>>> Signed-off-by: Daniel Axtens >>>> >>>> --- >>> >>>> +static void __init kasan_shallow_populate_pgds(void *start, void *end) >>>> +{ >>>> + unsigned long addr, next; >>>> + pgd_t *pgd; >>>> + void *p; >>>> + int nid = early_pfn_to_nid((unsigned long)start); >>> >>> This doesn't make sense. start is not even a pfn. With linear mapping >>> we try to identify nid to have the shadow on the same node as memory. But >>> in this case we don't have memory or the corresponding shadow (yet), >>> we only install pgd/p4d. >>> I guess we could just use NUMA_NO_NODE. >> >> Ah wow, that's quite the clanger on my part. >> >> There are a couple of other invocations of early_pfn_to_nid in that file >> that use an address directly, but at least they reference actual memory. >> I'll send a separate patch to fix those up. > > I see only one incorrect, in kasan_init(): early_pfn_to_nid(__pa(_stext)) > It should be wrapped with PFN_DOWN(). > Other usages in map_range() seems to be correct, range->start,end is pfns. > Oh, right, I didn't realise map_range was already using pfns. > >> >>> The rest looks ok, so with that fixed: >>> >>> Reviewed-by: Andrey Ryabinin >> >> Thanks heaps! I've fixed up the nit you identifed in the first patch, >> and I agree that the last patch probably isn't needed. I'll respin the >> series shortly. >> > > Hold on a sec, just spotted another thing to fix. > >> @@ -352,9 +397,24 @@ void __init kasan_init(void) >> shadow_cpu_entry_end = (void *)round_up( >> (unsigned long)shadow_cpu_entry_end, PAGE_SIZE); >> >> + /* >> + * If we're in full vmalloc mode, don't back vmalloc space with early >> + * shadow pages. Instead, prepopulate pgds/p4ds so they are synced to >> + * the global table and we can populate the lower levels on demand. >> + */ >> +#ifdef CONFIG_KASAN_VMALLOC >> + kasan_shallow_populate_pgds( >> + kasan_mem_to_shadow((void *)PAGE_OFFSET + MAXMEM), > > This should be VMALLOC_START, there is no point to allocate pgds for the hole between linear mapping > and vmalloc, just waste of memory. It make sense to map early shadow for that hole, because if code > dereferences address in that hole we will see the page fault on that address instead of fault on the shadow. > > So something like this might work: > > kasan_populate_early_shadow( > kasan_mem_to_shadow((void *)PAGE_OFFSET + MAXMEM), > kasan_mem_to_shadow((void *)VMALLOC_START)); > > if (IS_ENABLED(CONFIG_KASAN_VMALLOC) > kasan_shallow_populate_pgds(kasan_mem_to_shadow(VMALLOC_START), kasan_mem_to_shadow((void *)VMALLOC_END)) > else > kasan_populate_early_shadow(kasan_mem_to_shadow(VMALLOC_START), kasan_mem_to_shadow((void *)VMALLOC_END)); > > kasan_populate_early_shadow( > kasan_mem_to_shadow((void *)VMALLOC_END + 1), > shadow_cpu_entry_begin); Sounds good. It's getting late for me so I'll change and test that and send a respin tomorrow my time. Regards, Daniel