linux-kernel - [PATCH v9 18/19] KVM: selftests: Add ucall support for TDX

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250821042915.3712925-19-sagis@google.com>
Date: Wed, 20 Aug 2025 21:29:11 -0700
From: Sagi Shahar <sagis@...gle.com>
To: linux-kselftest@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>, 
	Shuah Khan <shuah@...nel.org>, Sean Christopherson <seanjc@...gle.com>, 
	Ackerley Tng <ackerleytng@...gle.com>, Ryan Afranji <afranji@...gle.com>, 
	Andrew Jones <ajones@...tanamicro.com>, Isaku Yamahata <isaku.yamahata@...el.com>, 
	Erdem Aktas <erdemaktas@...gle.com>, Rick Edgecombe <rick.p.edgecombe@...el.com>, 
	Sagi Shahar <sagis@...gle.com>, Roger Wang <runanwang@...gle.com>, 
	Binbin Wu <binbin.wu@...ux.intel.com>, Oliver Upton <oliver.upton@...ux.dev>, 
	"Pratik R. Sampat" <pratikrajesh.sampat@....com>, Reinette Chatre <reinette.chatre@...el.com>, 
	Ira Weiny <ira.weiny@...el.com>, Chao Gao <chao.gao@...el.com>, 
	Chenyi Qiang <chenyi.qiang@...el.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: [PATCH v9 18/19] KVM: selftests: Add ucall support for TDX

From: Ackerley Tng <ackerleytng@...gle.com>

ucalls for non-Coco VMs work by having the guest write to the rdi
register, then perform an io instruction to exit to the host. The host
then reads rdi using kvm_get_regs().

CPU registers can't be read using kvm_get_regs() for TDX, so TDX
guests use MMIO to pass the struct ucall's hva to the host. MMIO was
chosen because it is one of the simplest (hence unlikely to fail)
mechanisms that support passing 8 bytes from guest to host.

Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
Co-developed-by: Sagi Shahar <sagis@...gle.com>
Signed-off-by: Sagi Shahar <sagis@...gle.com>
---
 .../testing/selftests/kvm/include/x86/ucall.h |  4 +-
 tools/testing/selftests/kvm/lib/x86/ucall.c   | 45 ++++++++++++++++---
 2 files changed, 41 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/x86/ucall.h b/tools/testing/selftests/kvm/include/x86/ucall.h
index d3825dcc3cd9..0494a4a21557 100644
--- a/tools/testing/selftests/kvm/include/x86/ucall.h
+++ b/tools/testing/selftests/kvm/include/x86/ucall.h
@@ -6,8 +6,6 @@
 
 #define UCALL_EXIT_REASON       KVM_EXIT_IO
 
-static inline void ucall_arch_init(struct kvm_vm *vm, vm_paddr_t mmio_gpa)
-{
-}
+void ucall_arch_init(struct kvm_vm *vm, vm_paddr_t mmio_gpa);
 
 #endif
diff --git a/tools/testing/selftests/kvm/lib/x86/ucall.c b/tools/testing/selftests/kvm/lib/x86/ucall.c
index 1265cecc7dd1..0ad24baaa3c4 100644
--- a/tools/testing/selftests/kvm/lib/x86/ucall.c
+++ b/tools/testing/selftests/kvm/lib/x86/ucall.c
@@ -5,11 +5,34 @@
  * Copyright (C) 2018, Red Hat, Inc.
  */
 #include "kvm_util.h"
+#include "tdx/tdx.h"
 
 #define UCALL_PIO_PORT ((uint16_t)0x1000)
 
+static uint8_t vm_type;
+static vm_paddr_t host_ucall_mmio_gpa;
+static vm_paddr_t ucall_mmio_gpa;
+
+void ucall_arch_init(struct kvm_vm *vm, vm_paddr_t mmio_gpa)
+{
+	vm_type = vm->type;
+	sync_global_to_guest(vm, vm_type);
+
+	host_ucall_mmio_gpa = ucall_mmio_gpa = mmio_gpa;
+
+	if (vm_type == KVM_X86_TDX_VM)
+		ucall_mmio_gpa |= vm->arch.s_bit;
+
+	sync_global_to_guest(vm, ucall_mmio_gpa);
+}
+
 void ucall_arch_do_ucall(vm_vaddr_t uc)
 {
+	if (vm_type == KVM_X86_TDX_VM) {
+		tdg_vp_vmcall_ve_request_mmio_write(ucall_mmio_gpa, 8, uc);
+		return;
+	}
+
 	/*
 	 * FIXME: Revert this hack (the entire commit that added it) once nVMX
 	 * preserves L2 GPRs across a nested VM-Exit.  If a ucall from L2, e.g.
@@ -46,11 +69,23 @@ void *ucall_arch_get_ucall(struct kvm_vcpu *vcpu)
 {
 	struct kvm_run *run = vcpu->run;
 
-	if (run->exit_reason == KVM_EXIT_IO && run->io.port == UCALL_PIO_PORT) {
-		struct kvm_regs regs;
+	switch (vm_type) {
+	case KVM_X86_TDX_VM:
+		if (vcpu->run->exit_reason == KVM_EXIT_MMIO &&
+		    vcpu->run->mmio.phys_addr == host_ucall_mmio_gpa &&
+		    vcpu->run->mmio.len == 8 && vcpu->run->mmio.is_write) {
+			uint64_t data = *(uint64_t *)vcpu->run->mmio.data;
+
+			return (void *)data;
+		}
+		return NULL;
+	default:
+		if (run->exit_reason == KVM_EXIT_IO && run->io.port == UCALL_PIO_PORT) {
+			struct kvm_regs regs;
 
-		vcpu_regs_get(vcpu, &regs);
-		return (void *)regs.rdi;
+			vcpu_regs_get(vcpu, &regs);
+			return (void *)regs.rdi;
+		}
+		return NULL;
 	}
-	return NULL;
 }
-- 
2.51.0.rc1.193.gad69d77794-goog