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Subject[RFC PATCH 05/21] x86/virt/tdx: Detect P-SEAMLDR and TDX module
Date
P-SEAMLDR (persistent SEAM loader) is the first software module that
runs in SEAM VMX root, responsible for loading and updating the TDX
module. Both P-SEAMLDR and TDX module are expected to be loaded before
host kernel boots.

Detect P-SEAMLDR and TDX module by calling SEAMLDR.INFO SEAMCALL to get
the P-SEAMLDR information. If the SEAMCALL fails with VMfailInvalid,
both of them are not loaded. Otherwise, if the SEAMCALL succeeds, the
P-SEAMLDR information further tells whether the TDX module is loaded.

Also implement a wrapper of __seamcall() to make SEAMCALL to P-SEAMLDR
and TDX module with additional defensive check on SEAMRR and CR4.VMXE,
since both detecting and initializing TDX module require the caller of
TDX to handle VMXON.

Signed-off-by: Kai Huang <kai.huang@intel.com>
---
arch/x86/virt/vmx/tdx.c | 180 +++++++++++++++++++++++++++++++++++++++-
arch/x86/virt/vmx/tdx.h | 31 +++++++
2 files changed, 208 insertions(+), 3 deletions(-)

diff --git a/arch/x86/virt/vmx/tdx.c b/arch/x86/virt/vmx/tdx.c
index a85bc52c4690..35116eaa0c1a 100644
--- a/arch/x86/virt/vmx/tdx.c
+++ b/arch/x86/virt/vmx/tdx.c
@@ -15,7 +15,9 @@
#include <asm/msr.h>
#include <asm/cpufeature.h>
#include <asm/cpufeatures.h>
+#include <asm/virtext.h>
#include <asm/tdx.h>
+#include "tdx.h"

/* Support Intel Secure Arbitration Mode Range Registers (SEAMRR) */
#define MTRR_CAP_SEAMRR BIT(15)
@@ -74,6 +76,8 @@ static enum tdx_module_status_t tdx_module_status;
/* Prevent concurrent attempts on TDX detection and initialization */
static DEFINE_MUTEX(tdx_module_lock);

+static struct p_seamldr_info p_seamldr_info;
+
static bool __seamrr_enabled(void)
{
return (seamrr_mask & SEAMRR_ENABLED_BITS) == SEAMRR_ENABLED_BITS;
@@ -229,6 +233,161 @@ static bool tdx_keyid_sufficient(void)
return tdx_keyid_num >= 2;
}

+/*
+ * All error codes of both P-SEAMLDR and TDX module SEAMCALLs
+ * have bit 63 set if SEAMCALL fails.
+ */
+#define SEAMCALL_LEAF_ERROR(_ret) ((_ret) & BIT_ULL(63))
+
+/**
+ * seamcall - make SEAMCALL to P-SEAMLDR or TDX module with additional
+ * check on SEAMRR and CR4.VMXE
+ *
+ * @fn: SEAMCALL leaf number.
+ * @rcx: Input operand RCX.
+ * @rdx: Input operand RDX.
+ * @r8: Input operand R8.
+ * @r9: Input operand R9.
+ * @seamcall_ret: SEAMCALL completion status (can be NULL).
+ * @out: Additional output operands (can be NULL).
+ *
+ * Wrapper of __seamcall() to make SEAMCALL to TDX module or P-SEAMLDR
+ * with additional defensive check on SEAMRR and CR4.VMXE. Caller to
+ * make sure SEAMRR is enabled and CPU is already in VMX operation before
+ * calling this function.
+ *
+ * Unlike __seamcall(), it returns kernel error code instead of SEAMCALL
+ * completion status, which is returned via @seamcall_ret if desired.
+ *
+ * Return:
+ *
+ * * -ENODEV: SEAMCALL failed with VMfailInvalid, or SEAMRR is not enabled.
+ * * -EPERM: CR4.VMXE is not enabled
+ * * -EFAULT: SEAMCALL failed
+ * * -0: SEAMCALL succeeded
+ */
+static int seamcall(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
+ u64 *seamcall_ret, struct tdx_module_output *out)
+{
+ u64 ret;
+
+ if (WARN_ON_ONCE(!seamrr_enabled()))
+ return -ENODEV;
+
+ /*
+ * SEAMCALL instruction requires CPU being already in VMX
+ * operation (VMXON has been done), otherwise it causes #UD.
+ * Sanity check whether CR4.VMXE has been enabled.
+ *
+ * Note VMX being enabled in CR4 doesn't mean CPU is already
+ * in VMX operation, but unfortunately there's no way to do
+ * such check. However in practice enabling CR4.VMXE and
+ * doing VMXON are done together (for now) so in practice it
+ * checks whether VMXON has been done.
+ *
+ * Preemption is disabled during the CR4.VMXE check and the
+ * actual SEAMCALL so VMX doesn't get disabled by other threads
+ * due to scheduling.
+ */
+ preempt_disable();
+ if (WARN_ON_ONCE(!cpu_vmx_enabled())) {
+ preempt_enable_no_resched();
+ return -EPERM;
+ }
+
+ ret = __seamcall(fn, rcx, rdx, r8, r9, out);
+
+ preempt_enable_no_resched();
+
+ /*
+ * Convert SEAMCALL error code to kernel error code:
+ * - -ENODEV: VMfailInvalid
+ * - -EFAULT: SEAMCALL failed
+ * - 0: SEAMCALL was successful
+ */
+ if (ret == TDX_SEAMCALL_VMFAILINVALID)
+ return -ENODEV;
+
+ /* Save the completion status if caller wants to use it */
+ if (seamcall_ret)
+ *seamcall_ret = ret;
+
+ /*
+ * TDX module SEAMCALLs may also return non-zero completion
+ * status codes but w/o bit 63 set. Those codes are treated
+ * as additional information/warning while the SEAMCALL is
+ * treated as completed successfully. Return 0 in this case.
+ * Caller can use @seamcall_ret to get the additional code
+ * when it is desired.
+ */
+ if (SEAMCALL_LEAF_ERROR(ret)) {
+ pr_err("SEAMCALL leaf %llu failed: 0x%llx\n", fn, ret);
+ return -EFAULT;
+ }
+
+ return 0;
+}
+
+static inline bool p_seamldr_ready(void)
+{
+ return !!p_seamldr_info.p_seamldr_ready;
+}
+
+static inline bool tdx_module_ready(void)
+{
+ /*
+ * SEAMLDR_INFO.SEAM_READY indicates whether TDX module
+ * is (loaded and) ready for SEAMCALL.
+ */
+ return p_seamldr_ready() && !!p_seamldr_info.seam_ready;
+}
+
+/*
+ * Detect whether P-SEAMLDR has been loaded by calling SEAMLDR.INFO
+ * SEAMCALL to P-SEAMLDR information, which also contains whether
+ * the TDX module has been loaded and ready for SEAMCALL. Caller to
+ * make sure only calling this function when CPU is already in VMX
+ * operation.
+ */
+static int detect_p_seamldr(void)
+{
+ int ret;
+
+ /*
+ * SEAMCALL fails with VMfailInvalid when SEAM software is not
+ * loaded, in which case seamcall() returns -ENODEV. Use this
+ * to detect P-SEAMLDR.
+ *
+ * Note P-SEAMLDR SEAMCALL also fails with VMfailInvalid when
+ * P-SEAMLDR is already busy with another SEAMCALL. But this
+ * won't happen here as this function is only called once.
+ */
+ ret = seamcall(P_SEAMCALL_SEAMLDR_INFO, __pa(&p_seamldr_info),
+ 0, 0, 0, NULL, NULL);
+ if (ret) {
+ if (ret == -ENODEV)
+ pr_info("P-SEAMLDR is not loaded.\n");
+ else
+ pr_info("Failed to detect P-SEAMLDR.\n");
+
+ return ret;
+ }
+
+ /*
+ * If SEAMLDR.INFO was successful, it must be ready for SEAMCALL.
+ * Otherwise it's either kernel or firmware bug.
+ */
+ if (WARN_ON_ONCE(!p_seamldr_ready()))
+ return -ENODEV;
+
+ pr_info("P-SEAMLDR: version 0x%x, vendor_id: 0x%x, build_date: %u, build_num %u, major %u, minor %u\n",
+ p_seamldr_info.version, p_seamldr_info.vendor_id,
+ p_seamldr_info.build_date, p_seamldr_info.build_num,
+ p_seamldr_info.major, p_seamldr_info.minor);
+
+ return 0;
+}
+
static int __tdx_detect(void)
{
/*
@@ -247,7 +406,22 @@ static int __tdx_detect(void)
goto no_tdx_module;
}

- /* Return -ENODEV until TDX module is detected */
+ /*
+ * For simplicity any error during detect_p_seamldr() marks
+ * TDX module as not loaded.
+ */
+ if (detect_p_seamldr())
+ goto no_tdx_module;
+
+ if (!tdx_module_ready()) {
+ pr_info("TDX module is not loaded.\n");
+ goto no_tdx_module;
+ }
+
+ pr_info("TDX module detected.\n");
+ tdx_module_status = TDX_MODULE_LOADED;
+ return 0;
+
no_tdx_module:
tdx_module_status = TDX_MODULE_NONE;
return -ENODEV;
@@ -308,8 +482,8 @@ static int __tdx_init(void)
* tdx_detect - Detect whether the TDX module has been loaded
*
* Detect whether the TDX module has been loaded and ready for
- * initialization. Only call this function when CPU is already
- * in VMX operation.
+ * initialization. Only call this function when all cpus are
+ * already in VMX operation.
*
* This function can be called in parallel by multiple callers.
*
diff --git a/arch/x86/virt/vmx/tdx.h b/arch/x86/virt/vmx/tdx.h
index 9d5b6f554c20..6990c93198b3 100644
--- a/arch/x86/virt/vmx/tdx.h
+++ b/arch/x86/virt/vmx/tdx.h
@@ -3,6 +3,37 @@
#define _X86_VIRT_TDX_H

#include <linux/types.h>
+#include <linux/compiler.h>
+
+/*
+ * TDX architectural data structures
+ */
+
+#define P_SEAMLDR_INFO_ALIGNMENT 256
+
+struct p_seamldr_info {
+ u32 version;
+ u32 attributes;
+ u32 vendor_id;
+ u32 build_date;
+ u16 build_num;
+ u16 minor;
+ u16 major;
+ u8 reserved0[2];
+ u32 acm_x2apicid;
+ u8 reserved1[4];
+ u8 seaminfo[128];
+ u8 seam_ready;
+ u8 seam_debug;
+ u8 p_seamldr_ready;
+ u8 reserved2[88];
+} __packed __aligned(P_SEAMLDR_INFO_ALIGNMENT);
+
+/*
+ * P-SEAMLDR SEAMCALL leaf function
+ */
+#define P_SEAMLDR_SEAMCALL_BASE BIT_ULL(63)
+#define P_SEAMCALL_SEAMLDR_INFO (P_SEAMLDR_SEAMCALL_BASE | 0x0)

struct tdx_module_output;
u64 __seamcall(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
--
2.33.1
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