FAILED: patch "[PATCH] KVM: x86: Reject Hyper-V's SEND_IPI hypercalls if local APIC" failed to apply to 5.10-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x a8de7f100bb5989d9c3627d3a223ee1c863f3b69
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025021850-exes-cabana-e868@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a8de7f100bb5989d9c3627d3a223ee1c863f3b69 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@google.com>
Date: Fri, 17 Jan 2025 16:34:51 -0800
Subject: [PATCH] KVM: x86: Reject Hyper-V's SEND_IPI hypercalls if local APIC
 isn't in-kernel

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>

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 6a6dd5a84f22..6ebeb6cea6c0 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -2226,6 +2226,9 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
 	u32 vector;
 	bool all_cpus;
 
+	if (!lapic_in_kernel(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,
@@ -2852,7 +2855,8 @@ int kvm_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;