linux-kernel - Re: [PATCH v2] KVM: X86: Fix SMRAM accessing even if VM is shutdown

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Date:   Thu, 8 Feb 2018 11:24:18 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH v2] KVM: X86: Fix SMRAM accessing even if VM is shutdown

On 08/02/2018 08:32, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@...cent.com>
> 
> Reported by syzkaller:
> 
>    WARNING: CPU: 6 PID: 2434 at arch/x86/kvm/vmx.c:6660 handle_ept_misconfig+0x54/0x1e0 [kvm_intel]
>    CPU: 6 PID: 2434 Comm: repro_test Not tainted 4.15.0+ #4
>    RIP: 0010:handle_ept_misconfig+0x54/0x1e0 [kvm_intel]
>    Call Trace:
>     vmx_handle_exit+0xbd/0xe20 [kvm_intel]
>     kvm_arch_vcpu_ioctl_run+0xdaf/0x1d50 [kvm]
>     kvm_vcpu_ioctl+0x3e9/0x720 [kvm]
>     do_vfs_ioctl+0xa4/0x6a0
>     SyS_ioctl+0x79/0x90
>     entry_SYSCALL_64_fastpath+0x25/0x9c
> 
> The syzkaller creates a former thread to issue KVM_SMI ioctl, and then creates
> a latter thread to mmap and operate on the same vCPU, rsm emulation will not be 
> executed since there is no something like seabios which implements smi handler 
> when running syzkaller directly. This triggers a race condition when running 
> the testcase with multiple threads. Sometimes one thread exit w/ SHUTDOWN 
> reason, another thread mmaps and operates on the same vCPU, it continues to 
> use CS=0x30000, IP=0x8000 to access the address of SMI handler which results 
> in the above ept misconfig. This patch fixes it by returning RET_PF_EMULATE
> in kvm_handle_bad_page() which would cause an emulation failure and then an 
> exit with KVM_EXIT_INTERNAL_ERROR, the VM will stop instead of resetting and 
> be taken advantage of.
> 
> Reported-by: syzbot+c1d9517cab094dae65e446c0c5b4de6c40f4dc58@...kaller.appspotmail.com
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> ---
> v1 -> v2:
>  * return RET_PF_EMULATE
> 
>  arch/x86/kvm/mmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 8eca1d0..6c5a82c 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -3029,7 +3029,7 @@ static int kvm_handle_bad_page(struct kvm_vcpu *vcpu, gfn_t gfn, kvm_pfn_t pfn)
>  		return RET_PF_RETRY;
>  	}
>  
> -	return -EFAULT;
> +	return RET_PF_EMULATE;
>  }
>  
>  static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu,
> 

Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>