Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 13 Oct 2020 09:25:25 +0000
From:   Wei Liu <wei.liu@kernel.org>
To:     Sasha Levin <sashal@kernel.org>
Cc:     kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com,
        wei.liu@kernel.org, tglx@linutronix.de, mingo@redhat.com,
        bp@alien8.de, x86@kernel.org, hpa@zytor.com, vkuznets@redhat.com,
        mikelley@microsoft.com, linux-hyperv@vger.kernel.org,
        linux-kernel@vger.kernel.org, stable@kernel.org
Subject: Re: [PATCH v2 1/2] x86/hyper-v: guard against cpu mask changes in
 hyperv_flush_tlb_others()
Message-ID: <20201013092525.4po4glgjn2vodytf@liuwe-devbox-debian-v2>
References: <20201005233739.2560641-1-sashal@kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20201005233739.2560641-1-sashal@kernel.org>
User-Agent: NeoMutt/20180716
Precedence: bulk

On Mon, Oct 05, 2020 at 07:37:38PM -0400, Sasha Levin wrote:
> cpumask can change underneath us, which is generally safe except when we
> call into hv_cpu_number_to_vp_number(): if cpumask ends up empty we pass
> num_cpu_possible() into hv_cpu_number_to_vp_number(), causing it to read
> garbage. As reported by KASAN:
> 
> [   83.504763] BUG: KASAN: slab-out-of-bounds in hyperv_flush_tlb_others (include/asm-generic/mshyperv.h:128 arch/x86/hyperv/mmu.c:112)
> [   83.908636] Read of size 4 at addr ffff888267c01370 by task kworker/u8:2/106
> [   84.196669] CPU: 0 PID: 106 Comm: kworker/u8:2 Tainted: G        W         5.4.60 #1
> [   84.196669] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS 090008  12/07/2018
> [   84.196669] Workqueue: writeback wb_workfn (flush-8:0)
> [   84.196669] Call Trace:
> [   84.196669] dump_stack (lib/dump_stack.c:120)
> [   84.196669] print_address_description.constprop.0 (mm/kasan/report.c:375)
> [   84.196669] __kasan_report.cold (mm/kasan/report.c:507)
> [   84.196669] kasan_report (arch/x86/include/asm/smap.h:71 mm/kasan/common.c:635)
> [   84.196669] hyperv_flush_tlb_others (include/asm-generic/mshyperv.h:128 arch/x86/hyperv/mmu.c:112)
> [   84.196669] flush_tlb_mm_range (arch/x86/include/asm/paravirt.h:68 arch/x86/mm/tlb.c:798)
> [   84.196669] ptep_clear_flush (arch/x86/include/asm/tlbflush.h:586 mm/pgtable-generic.c:88)
> 

What is the easiest way to reproduce this? Just enable KASAN in the
guest and run it normally? I want to have a chance to verify my earlier
reply.

Thanks,
Wei.