linux-kernel - Re: [PATCH] KVM: X86: Fix read out-of-bounds vulnerability in kvm pio emulation

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Message-ID: <d3dc4ca8-0000-4cf6-b2b0-06bee400a8dd@redhat.com>
Date:   Fri, 19 May 2017 12:33:13 +0200
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>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Moguofang <moguofang@...wei.com>
Subject: Re: [PATCH] KVM: X86: Fix read out-of-bounds vulnerability in kvm pio
 emulation



On 19/05/2017 11:46, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@...mail.com>
> 
> Huawei folks reported a read out-of-bounds vulnerability in kvm pio emulation.
> 
> - "inb" instruction to access PIT Mod/Command register (ioport 0x43, write only, 
>   a read should be ignored) in guest can get a random number.
> - "rep insb" instruction to access PIT register port 0x43 can control memcpy() 
>   in emulator_pio_in_emulated() to copy max 0x400 bytes but only read 1 bytes, 
>   which will disclose the unimportant kernel memory in host but no crash.

The data comes simply from the last PIO read, right?  The vcpu struct is
zero-initialized, so there is no kernel memory leak---the byte was
already previously known to the guest.

Good catch though, and the patch looks good.

Thanks,

Paolo

> The similar test program below can reproduce the read out-of-bounds vulnerability: