Re: [PATCH v2 8/8] KVM: x86: Bug the VM on an out-of-bounds data read

Vitaly Kuznetsov
2022-06-01T08:39:22Z

Sean Christopherson <seanjc@google.com> writes:

> Bug the VM and terminate emulation if an out-of-bounds read into the
> emulator's data cache occurs. Knowingly contuining on all but guarantees
> that KVM will overwrite random kernel data, which is far, far worse than
> killing the VM.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/emulate.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 2aa17462a9ac..39ea9138224c 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -1373,7 +1373,8 @@ static int read_emulated(struct x86_emulate_ctxt *ctxt,
> if (mc->pos < mc->end)
> goto read_cached;
>
> - WARN_ON((mc->end + size) >= sizeof(mc->data));
> + if (KVM_EMULATOR_BUG_ON((mc->end + size) >= sizeof(mc->data), ctxt))
> + return X86EMUL_UNHANDLEABLE;
>
> rc = ctxt->ops->read_emulated(ctxt, addr, mc->data + mc->end, size,
> &ctxt->exception);

The last WARN_ON() is gone, cool)

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

--
Vitaly