Commit f8acb24a authored by Michael Kelley's avatar Michael Kelley Committed by Wei Liu
Browse files

x86/hyperv: Block root partition functionality in a Confidential VM 



Hyper-V should never specify a VM that is a Confidential VM and also
running in the root partition.  Nonetheless, explicitly block such a
combination to guard against a compromised Hyper-V maliciously trying to
exploit root partition functionality in a Confidential VM to expose
Confidential VM secrets. No known bug is being fixed, but the attack
surface for Confidential VMs on Hyper-V is reduced.

Signed-off-by: default avatarMichael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/1678894453-95392-1-git-send-email-mikelley@microsoft.com


Signed-off-by: default avatarWei Liu <wei.liu@kernel.org>
parent 1eb65c86

arch/x86/kernel/cpu/mshyperv.c

+8 −4
Original line number Diff line number Diff line
@@ -358,12 +358,16 @@ static void __init ms_hyperv_init_platform(void) 
	 * To mirror what Windows does we should extract CPU management

	 * features and use the ReservedIdentityBit to detect if Linux is the

	 * root partition. But that requires negotiating CPU management

	 * interface (a process to be finalized).

	 * interface (a process to be finalized). For now, use the privilege

	 * flag as the indicator for running as root.

	 *

	 * For now, use the privilege flag as the indicator for running as

	 * root.

	 * Hyper-V should never specify running as root and as a Confidential

	 * VM. But to protect against a compromised/malicious Hyper-V trying

	 * to exploit root behavior to expose Confidential VM memory, ignore

	 * the root partition setting if also a Confidential VM.

	 */

	if (cpuid_ebx(HYPERV_CPUID_FEATURES) & HV_CPU_MANAGEMENT) {

	if ((ms_hyperv.priv_high & HV_CPU_MANAGEMENT) &&

	    !(ms_hyperv.priv_high & HV_ISOLATION)) {

		hv_root_partition = true;

		pr_info("Hyper-V: running as root partition\n");

	}