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vmm: igvm: gate CPUID page read with runtime hypervisor check

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The SnpCpuidInfo allocation and guest_memory.read() call in the
isolated page import loop are only needed for KVM's CPUID page
retry logic. However, when building with both 'mshv' and 'kvm'
features, #[cfg(feature = "kvm")] alone is insufficient as a
guard because both features compile into the same binary.

Without a runtime hypervisor type check, this code executes on
MSHV as well, reading guest memory at arbitrary GPAs that may
not be valid in the MSHV memory layout. This can cause undefined
behavior or crashes during IGVM loading.

Add #[cfg(feature = "kvm")] to the variable declarations and
wrap the guest_memory.read() call in a runtime check for
HypervisorType::Kvm to ensure it only executes on KVM.

Assisted-by: Claude:Opus-4.6

Signed-off-by: Muminul Islam <muislam@microsoft.com>
This commit is contained in:
Muminul Islam
2026-04-29 15:35:04 -07:00
committed by Rob Bradford
parent 7d24608bcf
commit 4608de134f
1 changed files with 12 additions and 6 deletions
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18
vmm/src/igvm/igvm_loader.rs
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@@ -23,12 +23,14 @@ use log::info;
#[cfg(feature = "mshv")]
use mshv_bindings::*;
use thiserror::Error;
#[cfg(all(feature = "kvm", feature = "sev_snp"))]
use vm_memory::Bytes;
#[cfg(feature = "sev_snp")]
use vm_memory::{Bytes, GuestAddress, GuestAddressSpace, GuestMemory};
use vm_memory::{GuestAddress, GuestAddressSpace, GuestMemory};
#[cfg(all(feature = "kvm", feature = "sev_snp"))]
use vm_migration::Snapshottable;
use zerocopy::IntoBytes;
#[cfg(feature = "sev_snp")]
#[cfg(all(feature = "kvm", feature = "sev_snp"))]
use zerocopy::{FromBytes, FromZeros};
#[cfg(feature = "sev_snp")]
@@ -40,11 +42,11 @@ use crate::memory_manager::{Error as MemoryManagerError, MemoryManager};
#[cfg(feature = "sev_snp")]
const ISOLATED_PAGE_SHIFT: u32 = 12;
#[cfg(feature = "sev_snp")]
#[cfg(all(feature = "kvm", feature = "sev_snp"))]
const SNP_CPUID_LIMIT: u32 = 64;
// see section 7.1
// https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/56860.pdf
#[cfg(feature = "sev_snp")]
#[cfg(all(feature = "kvm", feature = "sev_snp"))]
#[repr(C)]
#[derive(Debug, Clone, PartialEq, Eq, IntoBytes, FromBytes)]
pub struct SnpCpuidFunc {
@@ -59,7 +61,7 @@ pub struct SnpCpuidFunc {
pub reserved: u64,
}
#[cfg(feature = "sev_snp")]
#[cfg(all(feature = "kvm", feature = "sev_snp"))]
#[repr(C)]
#[derive(Debug, Clone, FromBytes, IntoBytes)]
pub struct SnpCpuidInfo {
@@ -656,8 +658,12 @@ pub fn load_igvm(
.collect();
#[cfg(feature = "kvm")]
let page_type = group[0].page_type;
#[cfg(feature = "kvm")]
let mut new_cp = SnpCpuidInfo::new_zeroed();
let _ = guest_memory.read(new_cp.as_mut_bytes(), GuestAddress(group[0].gpa));
#[cfg(feature = "kvm")]
if hypervisor_type == HypervisorType::Kvm {
let _ = guest_memory.read(new_cp.as_mut_bytes(), GuestAddress(group[0].gpa));
}
let import_result = memory_manager
.lock()
.unwrap()