[PATCH 5.10.y] KVM: x86: Reject Hyper-V's SEND_IPI hypercalls if local APIC isn't in-kernel

[PATCH 5.10.y] KVM: x86: Reject Hyper-V's SEND_IPI hypercalls if local APIC isn't in-kernel

[Abdelkareem Abdelsaamad]

From: Sean Christopherson <seanjc@google.com>

commit a8de7f100bb5989d9c3627d3a223ee1c863f3b69 upstream.

Advertise support for Hyper-V's SEND_IPI and SEND_IPI_EX hypercalls if and
only if the local API is emulated/virtualized by KVM, and explicitly reject
said hypercalls if the local APIC is emulated in userspace, i.e. don't rely
on userspace to opt-in to KVM_CAP_HYPERV_ENFORCE_CPUID.

Rejecting SEND_IPI and SEND_IPI_EX fixes a NULL-pointer dereference if
Hyper-V enlightenments are exposed to the guest without an in-kernel local
APIC:

  dump_stack+0xbe/0xfd
  __kasan_report.cold+0x34/0x84
  kasan_report+0x3a/0x50
  __apic_accept_irq+0x3a/0x5c0
  kvm_hv_send_ipi.isra.0+0x34e/0x820
  kvm_hv_hypercall+0x8d9/0x9d0
  kvm_emulate_hypercall+0x506/0x7e0
  __vmx_handle_exit+0x283/0xb60
  vmx_handle_exit+0x1d/0xd0
  vcpu_enter_guest+0x16b0/0x24c0
  vcpu_run+0xc0/0x550
  kvm_arch_vcpu_ioctl_run+0x170/0x6d0
  kvm_vcpu_ioctl+0x413/0xb20
  __se_sys_ioctl+0x111/0x160
  do_syscal1_64+0x30/0x40
  entry_SYSCALL_64_after_hwframe+0x67/0xd1

Note, checking the sending vCPU is sufficient, as the per-VM irqchip_mode
can't be modified after vCPUs are created, i.e. if one vCPU has an
in-kernel local APIC, then all vCPUs have an in-kernel local APIC.

Reported-by: Dongjie Zou <zoudongjie@huawei.com>
Fixes: 214ff83d4473 ("KVM: x86: hyperv: implement PV IPI send hypercalls")
Fixes: 2bc39970e932 ("x86/kvm/hyper-v: Introduce KVM_GET_SUPPORTED_HV_CPUID")
Cc: stable@vger.kernel.org
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Link: https://lore.kernel.org/r/20250118003454.2619573-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[Conflict due to
72167a9d7da2 ("KVM: x86: hyper-v: Stop shadowing global 'current_vcpu'
variable")
not in the tree]
Signed-off-by: Abdelkareem Abdelsaamad <kareemem@amazon.com>
---
 arch/x86/kvm/hyperv.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 20eb8f55e1f1..e097faf12c82 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1618,6 +1618,9 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *current_vcpu, u64 ingpa, u64 outgpa,
 	u32 vector;
 	bool all_cpus;
 
+	if (!lapic_in_kernel(current_vcpu))
+		return HV_STATUS_INVALID_HYPERCALL_INPUT;
+
 	if (!ex) {
 		if (!fast) {
 			if (unlikely(kvm_read_guest(kvm, ingpa, &send_ipi,
@@ -2060,7 +2063,8 @@ int kvm_vcpu_ioctl_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
 			ent->eax |= HV_X64_REMOTE_TLB_FLUSH_RECOMMENDED;
 			ent->eax |= HV_X64_APIC_ACCESS_RECOMMENDED;
 			ent->eax |= HV_X64_RELAXED_TIMING_RECOMMENDED;
-			ent->eax |= HV_X64_CLUSTER_IPI_RECOMMENDED;
+			if (!vcpu || lapic_in_kernel(vcpu))
+				ent->eax |= HV_X64_CLUSTER_IPI_RECOMMENDED;
 			ent->eax |= HV_X64_EX_PROCESSOR_MASKS_RECOMMENDED;
 			if (evmcs_ver)
 				ent->eax |= HV_X64_ENLIGHTENED_VMCS_RECOMMENDED;
-- 
2.47.1

Re: [PATCH 5.10.y] KVM: x86: Reject Hyper-V's SEND_IPI hypercalls if local APIC isn't in-kernel

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

✅ All tests passed successfully. No issues detected.
No action required from the submitter.

The upstream commit SHA1 provided is correct: a8de7f100bb5989d9c3627d3a223ee1c863f3b69

WARNING: Author mismatch between patch and upstream commit:
Backport author: Abdelkareem Abdelsaamad<kareemem@amazon.com>
Commit author: Sean Christopherson<seanjc@google.com>

Status in newer kernel trees:
6.13.y | Present (different SHA1: ca29f58ca374)
6.12.y | Present (different SHA1: aca8be4403fb)
6.6.y | Present (different SHA1: 874ff13c73c4)
6.1.y | Present (different SHA1: 5393cf223124)
5.15.y | Present (different SHA1: 8c0bc4fec456)

Note: The patch differs from the upstream commit:
---
1:  a8de7f100bb59 ! 1:  26c34724741d5 KVM: x86: Reject Hyper-V's SEND_IPI hypercalls if local APIC isn't in-kernel
    @@ Metadata
      ## Commit message ##
         KVM: x86: Reject Hyper-V's SEND_IPI hypercalls if local APIC isn't in-kernel
     
    +    commit a8de7f100bb5989d9c3627d3a223ee1c863f3b69 upstream.
    +
         Advertise support for Hyper-V's SEND_IPI and SEND_IPI_EX hypercalls if and
         only if the local API is emulated/virtualized by KVM, and explicitly reject
         said hypercalls if the local APIC is emulated in userspace, i.e. don't rely
    @@ Commit message
         Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
         Link: https://lore.kernel.org/r/20250118003454.2619573-2-seanjc@google.com
         Signed-off-by: Sean Christopherson <seanjc@google.com>
    +    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    +    [Conflict due to
    +    72167a9d7da2 ("KVM: x86: hyper-v: Stop shadowing global 'current_vcpu'
    +    variable")
    +    not in the tree]
    +    Signed-off-by: Abdelkareem Abdelsaamad <kareemem@amazon.com>
     
      ## arch/x86/kvm/hyperv.c ##
    -@@ arch/x86/kvm/hyperv.c: static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
    +@@ arch/x86/kvm/hyperv.c: static u64 kvm_hv_send_ipi(struct kvm_vcpu *current_vcpu, u64 ingpa, u64 outgpa,
      	u32 vector;
      	bool all_cpus;
      
    -+	if (!lapic_in_kernel(vcpu))
    ++	if (!lapic_in_kernel(current_vcpu))
     +		return HV_STATUS_INVALID_HYPERCALL_INPUT;
     +
    - 	if (hc->code == HVCALL_SEND_IPI) {
    - 		if (!hc->fast) {
    - 			if (unlikely(kvm_read_guest(kvm, hc->ingpa, &send_ipi,
    -@@ arch/x86/kvm/hyperv.c: int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
    + 	if (!ex) {
    + 		if (!fast) {
    + 			if (unlikely(kvm_read_guest(kvm, ingpa, &send_ipi,
    +@@ arch/x86/kvm/hyperv.c: int kvm_vcpu_ioctl_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
      			ent->eax |= HV_X64_REMOTE_TLB_FLUSH_RECOMMENDED;
      			ent->eax |= HV_X64_APIC_ACCESS_RECOMMENDED;
      			ent->eax |= HV_X64_RELAXED_TIMING_RECOMMENDED;
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-5.10.y       |  Success    |  Success   |