Re: [sos-linux-ext-patches] [RFC 04/14] x86/apic: Initialize APIC backing page for Secure AVIC

["Melody (Huibo) Wang" <huibo.wang@amd.com>]

Hi Neeraj,

On 9/13/2024 4:36 AM, Neeraj Upadhyay wrote:

> +static void init_backing_page(void *backing_page)
> +{
> +	u32 val;
> +	int i;
> +
> +	val = read_msr_from_hv(APIC_LVR);
> +	set_reg(backing_page, APIC_LVR, val);
> +

When you read the register from hypervisor, there is certain value defined in APM Table 16-2. APIC Registers, says APIC_LVR has value 80??0010h out of reset.

More specifically, Bit 31 is set which means the presence of extended APIC registers, and Bit 4 is set which is part of version number: "The local APIC implementation is identified with a value=1Xh (20h-FFh are
reserved)".

I think you should verify those values instead of just reading from the hypervisor. Also, I think you probably should verify all of registers you read from the hypervisor before you use them in the guest. In other words, sanitize the inputs from the hypervisor. 

Thanks,
Melody