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From: Binbin Wu <binbin.wu@linux.intel.com>
To: pbonzini@redhat.com,
xiaoyao.li@intel.com,
qemu-devel@nongnu.org
Cc: seanjc@google.com, michael.roth@amd.com, rick.p.edgecombe@intel.com,
isaku.yamahata@intel.com, farrah.chen@intel.com, kvm@vger.kernel.org,
binbin.wu@linux.intel.com
Subject: [PATCH] i386/kvm: Set return value after handling KVM_EXIT_HYPERCALL
Date: Thu, 12 Dec 2024 11:26:28 +0800
Message-ID: <20241212032628.475976-1-binbin.wu@linux.intel.com>
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Userspace should set the ret field of hypercall after handling
KVM_EXIT_HYPERCALL. Otherwise, a stale value could be returned to KVM.
Fixes: 47e76d03b15 ("i386/kvm: Add KVM_EXIT_HYPERCALL handling for KVM_HC_M=
AP_GPA_RANGE")
Reported-by: Farrah Chen <farrah.chen@intel.com>
Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
Tested-by: Farrah Chen <farrah.chen@intel.com>
---
To test the TDX code in kvm-coco-queue, please apply the patch to the QEMU,
otherwise, TDX guest boot could fail.
A matching QEMU tree including this patch is here:
https://github.com/intel-staging/qemu-tdx/releases/tag/tdx-qemu-upstream-v6=
.1-fix_kvm_hypercall_return_value
Previously, the issue was not triggered because no one would modify the ret
value. But with the refactor patch for __kvm_emulate_hypercall() in KVM,
https://lore.kernel.org/kvm/20241128004344.4072099-7-seanjc@google.com/, the
value could be modified.
---
target/i386/kvm/kvm.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index 8e17942c3b..4bcccb48d1 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -6005,10 +6005,14 @@ static int kvm_handle_hc_map_gpa_range(struct kvm_r=
un *run)
=20
static int kvm_handle_hypercall(struct kvm_run *run)
{
+ int ret =3D -EINVAL;
+
if (run->hypercall.nr =3D=3D KVM_HC_MAP_GPA_RANGE)
- return kvm_handle_hc_map_gpa_range(run);
+ ret =3D kvm_handle_hc_map_gpa_range(run);
+
+ run->hypercall.ret =3D ret;
=20
- return -EINVAL;
+ return ret;
}
=20
#define VMX_INVALID_GUEST_STATE 0x80000021
base-commit: ae35f033b874c627d81d51070187fbf55f0bf1a7
--=20
2.46.0