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Message-ID: <1a1172db-12f6-1173-b526-89e4da00e96a@gmail.com>
Date:   Fri, 25 Mar 2022 18:51:40 +0300
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Subject: Re: [syzbot] general protection fault in kvm_mmu_uninit_tdp_mmu
Content-Language: en-US
To:     syzbot <syzbot+717ed82268812a643b28@syzkaller.appspotmail.com>,
        bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com,
        jmattson@google.com, joro@8bytes.org, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, mingo@redhat.com,
        pbonzini@redhat.com, seanjc@google.com,
        syzkaller-bugs@googlegroups.com, tglx@linutronix.de,
        vkuznets@redhat.com, wanpengli@tencent.com, x86@kernel.org
References: <000000000000a5cb1305db0aaf48@google.com>
From:   Pavel Skripkin <paskripkin@gmail.com>
In-Reply-To: <000000000000a5cb1305db0aaf48@google.com>
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On 3/25/22 16:10, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    f9006d9269ea Add linux-next specific files for 20220321
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=101191bd700000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c1619ffa2b0259a1
> dashboard link: https://syzkaller.appspot.com/bug?extid=717ed82268812a643b28
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=109e8f5d700000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1666180b700000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+717ed82268812a643b28@syzkaller.appspotmail.com
> 

The following code is not safe:

arch/x86/kvm/mmu/tdp_mmu.c:

28	kvm->arch.tdp_mmu_zap_wq =
29		alloc_workqueue("kvm", WQ_UNBOUND|WQ_MEM_RECLAIM|WQ_CPU_INTENSIVE, 0);
30
31	return true;


Looks like kvm_mmu_init_tdp_mmu() error value is just ignored, and then 
all kvm_*_init_vm() functions are void, so the easiest solution is to 
check that tdp_mmu_zap_wq is valid pointer


#syz test: 
git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master


With regards,
Pavel Skripkin
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