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

[Paolo Bonzini]

On 19/05/2017 11:46, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> 
> 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: