[PATCHv2 01/29] x86/tdx: Detect running as a TDX guest in early boot

Kirill A. Shutemov
2022-01-24T15:02:19Z

From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

cc_platform_has() API is used in the kernel to enable confidential
computing features. Since TDX guest is a confidential computing
platform, it also needs to use this API.

In preparation of extending cc_platform_has() API to support TDX guest,
use CPUID instruction to detect support for TDX guests in the early
boot code (via tdx_early_init()). Since copy_bootdata() is the first
user of cc_platform_has() API, detect the TDX guest status before it.

Since cc_plaform_has() API will be used frequently across the boot
code, instead of repeatedly detecting the TDX guest status using the
CPUID instruction, detect once and cache the result. Add a function
(is_tdx_guest()) to read the cached TDX guest status in CC APIs.

Define a synthetic feature flag (X86_FEATURE_TDX_GUEST) and set this
bit in a valid TDX guest platform. This feature bit will be used to
do TDX-specific handling in some areas of the ARCH code where a
function call to check for TDX guest status is not cost-effective
(for example, TDX hypercall support).

Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/x86/Kconfig | 12 +++++++++
arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/include/asm/disabled-features.h | 8 +++++-
arch/x86/include/asm/tdx.h | 23 ++++++++++++++++++
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/head64.c | 4 +++
arch/x86/kernel/tdx.c | 31 ++++++++++++++++++++++++
7 files changed, 79 insertions(+), 1 deletion(-)
create mode 100644 arch/x86/include/asm/tdx.h
create mode 100644 arch/x86/kernel/tdx.c

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6fddb63271d9..09e6744af3f8 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -880,6 +880,18 @@ config ACRN_GUEST
IOT with small footprint and real-time features. More details can be
found in https://projectacrn.org/.

+config INTEL_TDX_GUEST
+ bool "Intel TDX (Trust Domain Extensions) - Guest Support"
+ depends on X86_64 && CPU_SUP_INTEL
+ depends on X86_X2APIC
+ help
+ Support running as a guest under Intel TDX. Without this support,
+ the guest kernel can not boot or run under TDX.
+ TDX includes memory encryption and integrity capabilities
+ which protect the confidentiality and integrity of guest
+ memory contents and CPU state. TDX guests are protected from
+ potential attacks from the VMM.
+
endif #HYPERVISOR_GUEST

source "arch/x86/Kconfig.cpu"
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 6db4e2932b3d..defed3bd543b 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -238,6 +238,7 @@
#define X86_FEATURE_VMW_VMMCALL ( 8*32+19) /* "" VMware prefers VMMCALL hypercall instruction */
#define X86_FEATURE_PVUNLOCK ( 8*32+20) /* "" PV unlock function */
#define X86_FEATURE_VCPUPREEMPT ( 8*32+21) /* "" PV vcpu_is_preempted function */
+#define X86_FEATURE_TDX_GUEST ( 8*32+22) /* Intel Trust Domain Extensions Guest */

/* Intel-defined CPU features, CPUID level 0x00000007:0 (EBX), word 9 */
#define X86_FEATURE_FSGSBASE ( 9*32+ 0) /* RDFSBASE, WRFSBASE, RDGSBASE, WRGSBASE instructions*/
diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
index 8f28fafa98b3..f556086e6093 100644
--- a/arch/x86/include/asm/disabled-features.h
+++ b/arch/x86/include/asm/disabled-features.h
@@ -65,6 +65,12 @@
# define DISABLE_SGX (1 << (X86_FEATURE_SGX & 31))
#endif

+#ifdef CONFIG_INTEL_TDX_GUEST
+# define DISABLE_TDX_GUEST 0
+#else
+# define DISABLE_TDX_GUEST (1 << (X86_FEATURE_TDX_GUEST & 31))
+#endif
+
/*
* Make sure to add features to the correct mask
*/
@@ -76,7 +82,7 @@
#define DISABLED_MASK5 0
#define DISABLED_MASK6 0
#define DISABLED_MASK7 (DISABLE_PTI)
-#define DISABLED_MASK8 0
+#define DISABLED_MASK8 (DISABLE_TDX_GUEST)
#define DISABLED_MASK9 (DISABLE_SMAP|DISABLE_SGX)
#define DISABLED_MASK10 0
#define DISABLED_MASK11 0
diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
new file mode 100644
index 000000000000..e375a950a033
--- /dev/null
+++ b/arch/x86/include/asm/tdx.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) 2021-2022 Intel Corporation */
+#ifndef _ASM_X86_TDX_H
+#define _ASM_X86_TDX_H
+
+#include <linux/init.h>
+
+#define TDX_CPUID_LEAF_ID 0x21
+#define TDX_IDENT "IntelTDX "
+
+#ifdef CONFIG_INTEL_TDX_GUEST
+
+void __init tdx_early_init(void);
+bool is_tdx_guest(void);
+
+#else
+
+static inline void tdx_early_init(void) { };
+static inline bool is_tdx_guest(void) { return false; }
+
+#endif /* CONFIG_INTEL_TDX_GUEST */
+
+#endif /* _ASM_X86_TDX_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 6aef9ee28a39..211d9fcdd729 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -130,6 +130,7 @@ obj-$(CONFIG_PARAVIRT_CLOCK) += pvclock.o
obj-$(CONFIG_X86_PMEM_LEGACY_DEVICE) += pmem.o

obj-$(CONFIG_JAILHOUSE_GUEST) += jailhouse.o
+obj-$(CONFIG_INTEL_TDX_GUEST) += tdx.o

obj-$(CONFIG_EISA) += eisa.o
obj-$(CONFIG_PCSPKR_PLATFORM) += pcspeaker.o
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index de563db9cdcd..1cb6346ec3d1 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -40,6 +40,7 @@
#include <asm/extable.h>
#include <asm/trapnr.h>
#include <asm/sev.h>
+#include <asm/tdx.h>

/*
* Manage page tables very early on.
@@ -516,6 +517,9 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)

copy_bootdata(__va(real_mode_data));

+ /* Needed before cc_platform_has() can be used for TDX */
+ tdx_early_init();
+
/*
* Load microcode early on BSP.
*/
diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
new file mode 100644
index 000000000000..1ef6979a6434
--- /dev/null
+++ b/arch/x86/kernel/tdx.c
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2021-2022 Intel Corporation */
+
+#undef pr_fmt
+#define pr_fmt(fmt) "tdx: " fmt
+
+#include <linux/cpufeature.h>
+#include <asm/tdx.h>
+
+static bool tdx_guest_detected __ro_after_init;
+
+bool is_tdx_guest(void)
+{
+ return tdx_guest_detected;
+}
+
+void __init tdx_early_init(void)
+{
+ u32 eax, sig[3];
+
+ cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2], &sig[1]);
+
+ if (memcmp(TDX_IDENT, sig, 12))
+ return;
+
+ tdx_guest_detected = true;
+
+ setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);
+
+ pr_info("Guest detected\n");
+}
--
2.34.1