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Date: Mon, 16 Jul 2018 10:09:12 -0700
From: Marc Orr <marcorr@...gle.com>
To: gregkh@...uxfoundation.org
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
syzkaller@...glegroups.com, rkrcmar@...hat.com
Subject: Re: [PATCH 4.17 62/67] kvm: vmx: Nested VM-entry prereqs for event inj.
On Mon, Jul 16, 2018 at 12:39 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> 4.17-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: Marc Orr <marcorr@...gle.com>
>
> commit 0447378a4a793da008451fad50bc0f93e9675ae6 upstream.
>
> This patch extends the checks done prior to a nested VM entry.
> Specifically, it extends the check_vmentry_prereqs function with checks
> for fields relevant to the VM-entry event injection information, as
> described in the Intel SDM, volume 3.
>
> This patch is motivated by a syzkaller bug, where a bad VM-entry
> interruption information field is generated in the VMCS02, which causes
> the nested VM launch to fail. Then, KVM fails to resume L1.
>
> While KVM should be improved to correctly resume L1 execution after a
> failed nested launch, this change is justified because the existing code
> to resume L1 is flaky/ad-hoc and the test coverage for resuming L1 is
> sparse.
>
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Signed-off-by: Marc Orr <marcorr@...gle.com>
> [Removed comment whose parts were describing previous revisions and the
> rest was obvious from function/variable naming. - Radim]
> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>
> ---
> arch/x86/include/asm/vmx.h | 3 ++
> arch/x86/kvm/vmx.c | 67 +++++++++++++++++++++++++++++++++++++++++++++
> arch/x86/kvm/x86.h | 9 ++++++
> 3 files changed, 79 insertions(+)
>
> --- a/arch/x86/include/asm/vmx.h
> +++ b/arch/x86/include/asm/vmx.h
> @@ -114,6 +114,7 @@
> #define VMX_MISC_PREEMPTION_TIMER_RATE_MASK 0x0000001f
> #define VMX_MISC_SAVE_EFER_LMA 0x00000020
> #define VMX_MISC_ACTIVITY_HLT 0x00000040
> +#define VMX_MISC_ZERO_LEN_INS 0x40000000
>
> /* VMFUNC functions */
> #define VMX_VMFUNC_EPTP_SWITCHING 0x00000001
> @@ -349,11 +350,13 @@ enum vmcs_field {
> #define VECTORING_INFO_VALID_MASK INTR_INFO_VALID_MASK
>
> #define INTR_TYPE_EXT_INTR (0 << 8) /* external interrupt */
> +#define INTR_TYPE_RESERVED (1 << 8) /* reserved */
> #define INTR_TYPE_NMI_INTR (2 << 8) /* NMI */
> #define INTR_TYPE_HARD_EXCEPTION (3 << 8) /* processor exception */
> #define INTR_TYPE_SOFT_INTR (4 << 8) /* software interrupt */
> #define INTR_TYPE_PRIV_SW_EXCEPTION (5 << 8) /* ICE breakpoint - undocumented */
> #define INTR_TYPE_SOFT_EXCEPTION (6 << 8) /* software exception */
> +#define INTR_TYPE_OTHER_EVENT (7 << 8) /* other event */
>
> /* GUEST_INTERRUPTIBILITY_INFO flags. */
> #define GUEST_INTR_STATE_STI 0x00000001
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -1510,6 +1510,17 @@ static inline unsigned nested_cpu_vmx_mi
> return vmx_misc_cr3_count(to_vmx(vcpu)->nested.msrs.misc_low);
> }
>
> +static inline bool nested_cpu_has_zero_length_injection(struct kvm_vcpu *vcpu)
> +{
> + return to_vmx(vcpu)->nested.msrs.misc_low & VMX_MISC_ZERO_LEN_INS;
> +}
> +
> +static inline bool nested_cpu_supports_monitor_trap_flag(struct kvm_vcpu *vcpu)
> +{
> + return to_vmx(vcpu)->nested.msrs.procbased_ctls_high &
> + CPU_BASED_MONITOR_TRAP_FLAG;
> +}
> +
> static inline bool nested_cpu_has(struct vmcs12 *vmcs12, u32 bit)
> {
> return vmcs12->cpu_based_vm_exec_control & bit;
> @@ -11364,6 +11375,62 @@ static int check_vmentry_prereqs(struct
> !nested_cr3_valid(vcpu, vmcs12->host_cr3))
> return VMXERR_ENTRY_INVALID_HOST_STATE_FIELD;
>
> + /*
> + * From the Intel SDM, volume 3:
> + * Fields relevant to VM-entry event injection must be set properly.
> + * These fields are the VM-entry interruption-information field, the
> + * VM-entry exception error code, and the VM-entry instruction length.
> + */
> + if (vmcs12->vm_entry_intr_info_field & INTR_INFO_VALID_MASK) {
> + u32 intr_info = vmcs12->vm_entry_intr_info_field;
> + u8 vector = intr_info & INTR_INFO_VECTOR_MASK;
> + u32 intr_type = intr_info & INTR_INFO_INTR_TYPE_MASK;
> + bool has_error_code = intr_info & INTR_INFO_DELIVER_CODE_MASK;
> + bool should_have_error_code;
> + bool urg = nested_cpu_has2(vmcs12,
> + SECONDARY_EXEC_UNRESTRICTED_GUEST);
> + bool prot_mode = !urg || vmcs12->guest_cr0 & X86_CR0_PE;
> +
> + /* VM-entry interruption-info field: interruption type */
> + if (intr_type == INTR_TYPE_RESERVED ||
> + (intr_type == INTR_TYPE_OTHER_EVENT &&
> + !nested_cpu_supports_monitor_trap_flag(vcpu)))
> + return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
> +
> + /* VM-entry interruption-info field: vector */
> + if ((intr_type == INTR_TYPE_NMI_INTR && vector != NMI_VECTOR) ||
> + (intr_type == INTR_TYPE_HARD_EXCEPTION && vector > 31) ||
> + (intr_type == INTR_TYPE_OTHER_EVENT && vector != 0))
> + return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
> +
> + /* VM-entry interruption-info field: deliver error code */
> + should_have_error_code =
> + intr_type == INTR_TYPE_HARD_EXCEPTION && prot_mode &&
> + x86_exception_has_error_code(vector);
> + if (has_error_code != should_have_error_code)
> + return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
> +
> + /* VM-entry exception error code */
> + if (has_error_code &&
> + vmcs12->vm_entry_exception_error_code & GENMASK(31, 15))
> + return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
> +
> + /* VM-entry interruption-info field: reserved bits */
> + if (intr_info & INTR_INFO_RESVD_BITS_MASK)
> + return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
> +
> + /* VM-entry instruction length */
> + switch (intr_type) {
> + case INTR_TYPE_SOFT_EXCEPTION:
> + case INTR_TYPE_SOFT_INTR:
> + case INTR_TYPE_PRIV_SW_EXCEPTION:
> + if ((vmcs12->vm_entry_instruction_len > 15) ||
> + (vmcs12->vm_entry_instruction_len == 0 &&
> + !nested_cpu_has_zero_length_injection(vcpu)))
> + return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
> + }
> + }
> +
> return 0;
> }
>
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -110,6 +110,15 @@ static inline bool is_la57_mode(struct k
> #endif
> }
>
> +static inline bool x86_exception_has_error_code(unsigned int vector)
> +{
> + static u32 exception_has_error_code = BIT(DF_VECTOR) | BIT(TS_VECTOR) |
> + BIT(NP_VECTOR) | BIT(SS_VECTOR) | BIT(GP_VECTOR) |
> + BIT(PF_VECTOR) | BIT(AC_VECTOR);
> +
> + return (1U << vector) & exception_has_error_code;
> +}
> +
> static inline bool mmu_is_nested(struct kvm_vcpu *vcpu)
> {
> return vcpu->arch.walk_mmu == &vcpu->arch.nested_mmu;
>
>
Reviewed-by: Marc Orr <marcorr@...gle.com>
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