Messages in this thread Patch in this message | | | From | Michael Kelley <> | Subject | [PATCH 1/1] x86/hyperv: Block root partition functionality in a Confidential VM | Date | Wed, 15 Mar 2023 08:34:13 -0700 |
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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: Michael Kelley <mikelley@microsoft.com> --- arch/x86/kernel/cpu/mshyperv.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c index ff348eb..ac630ec 100644 --- a/arch/x86/kernel/cpu/mshyperv.c +++ b/arch/x86/kernel/cpu/mshyperv.c @@ -356,12 +356,16 @@ 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"); } -- 1.8.3.1
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