[PATCH v11 05/20] x86/virt/tdx: Add SEAMCALL infrastructure

From: Kai Huang
Date: Sun Jun 04 2023 - 10:29:24 EST

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TDX introduces a new CPU mode: Secure Arbitration Mode (SEAM). This
mode runs only the TDX module itself or other code to load the TDX
module.

The host kernel communicates with SEAM software via a new SEAMCALL
instruction. This is conceptually similar to a guest->host hypercall,
except it is made from the host to SEAM software instead. The TDX
module establishes a new SEAMCALL ABI which allows the host to
initialize the module and to manage VMs.

Add infrastructure to make SEAMCALLs. The SEAMCALL ABI is very similar
to the TDCALL ABI and leverages much TDCALL infrastructure.

SEAMCALL instruction causes #GP when TDX isn't BIOS enabled, and #UD
when CPU is not in VMX operation. Currently, only KVM code mocks with
VMX enabling, and KVM is the only user of TDX. This implementation
chooses to make KVM itself responsible for enabling VMX before using
TDX and let the rest of the kernel stay blissfully unaware of VMX.

The current TDX_MODULE_CALL macro handles neither #GP nor #UD. The
kernel would hit Oops if SEAMCALL were mistakenly made w/o enabling VMX
first. Architecturally, there is no CPU flag to check whether the CPU
is in VMX operation. Also, if a BIOS were buggy, it could still report
valid TDX private KeyIDs when TDX actually couldn't be enabled.

Extend the TDX_MODULE_CALL macro to handle #UD and #GP to return error
codes. Introduce two new TDX error codes for them respectively so the
caller can distinguish.

Also add a wrapper function of SEAMCALL to convert SEAMCALL error code
to the kernel error code, and print out SEAMCALL error code to help the
user to understand what went wrong.

Signed-off-by: Kai Huang <kai.huang@xxxxxxxxx>
---

v10 -> v11:
- No update

v9 -> v10:
- Make the TDX_SEAMCALL_{GP|UD} error codes unconditional but doesn't
define them when INTEL_TDX_HOST is enabled. (Dave)
- Slightly improved changelog to explain why add assembly code to handle
#UD and #GP.

v8 -> v9:
- Changed patch title (Dave).
- Enhanced seamcall() to include the cpu id to the error message when
SEAMCALL fails.

v7 -> v8:
- Improved changelog (Dave):
- Trim down some sentences (Dave).
- Removed __seamcall() and seamcall() function name and changed
accordingly (Dave).
- Improved the sentence explaining why to handle #GP (Dave).
- Added code to print out error message in seamcall(), following
the idea that tdx_enable() to return universal error and print out
error message to make clear what's going wrong (Dave). Also mention
this in changelog.

v6 -> v7:
- No change.

v5 -> v6:
- Added code to handle #UD and #GP (Dave).
- Moved the seamcall() wrapper function to this patch, and used a
temporary __always_unused to avoid compile warning (Dave).

- v3 -> v5 (no feedback on v4):
- Explicitly tell TDX_SEAMCALL_VMFAILINVALID is returned if the
SEAMCALL itself fails.
- Improve the changelog.

---
arch/x86/include/asm/tdx.h | 5 +++
arch/x86/virt/vmx/tdx/Makefile | 2 +-
arch/x86/virt/vmx/tdx/seamcall.S | 52 +++++++++++++++++++++++++++++
arch/x86/virt/vmx/tdx/tdx.c | 56 ++++++++++++++++++++++++++++++++
arch/x86/virt/vmx/tdx/tdx.h | 10 ++++++
arch/x86/virt/vmx/tdx/tdxcall.S | 19 +++++++++--
6 files changed, 141 insertions(+), 3 deletions(-)
create mode 100644 arch/x86/virt/vmx/tdx/seamcall.S
create mode 100644 arch/x86/virt/vmx/tdx/tdx.h

diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 4dfe2e794411..b489b5b9de5d 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -8,6 +8,8 @@
#include <asm/ptrace.h>
#include <asm/shared/tdx.h>

+#include <asm/trapnr.h>
+
/*
* SW-defined error codes.
*
@@ -18,6 +20,9 @@
#define TDX_SW_ERROR (TDX_ERROR | GENMASK_ULL(47, 40))
#define TDX_SEAMCALL_VMFAILINVALID (TDX_SW_ERROR | _UL(0xFFFF0000))

+#define TDX_SEAMCALL_GP (TDX_SW_ERROR | X86_TRAP_GP)
+#define TDX_SEAMCALL_UD (TDX_SW_ERROR | X86_TRAP_UD)
+
#ifndef __ASSEMBLY__

/* TDX supported page sizes from the TDX module ABI. */
diff --git a/arch/x86/virt/vmx/tdx/Makefile b/arch/x86/virt/vmx/tdx/Makefile
index 93ca8b73e1f1..38d534f2c113 100644
--- a/arch/x86/virt/vmx/tdx/Makefile
+++ b/arch/x86/virt/vmx/tdx/Makefile
@@ -1,2 +1,2 @@
# SPDX-License-Identifier: GPL-2.0-only
-obj-y += tdx.o
+obj-y += tdx.o seamcall.o
diff --git a/arch/x86/virt/vmx/tdx/seamcall.S b/arch/x86/virt/vmx/tdx/seamcall.S
new file mode 100644
index 000000000000..f81be6b9c133
--- /dev/null
+++ b/arch/x86/virt/vmx/tdx/seamcall.S
@@ -0,0 +1,52 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/linkage.h>
+#include <asm/frame.h>
+
+#include "tdxcall.S"
+
+/*
+ * __seamcall() - Host-side interface functions to SEAM software module
+ * (the P-SEAMLDR or the TDX module).
+ *
+ * Transform function call register arguments into the SEAMCALL register
+ * ABI. Return TDX_SEAMCALL_VMFAILINVALID if the SEAMCALL itself fails,
+ * or the completion status of the SEAMCALL leaf function. Additional
+ * output operands are saved in @out (if it is provided by the caller).
+ *
+ *-------------------------------------------------------------------------
+ * SEAMCALL ABI:
+ *-------------------------------------------------------------------------
+ * Input Registers:
+ *
+ * RAX - SEAMCALL Leaf number.
+ * RCX,RDX,R8-R9 - SEAMCALL Leaf specific input registers.
+ *
+ * Output Registers:
+ *
+ * RAX - SEAMCALL completion status code.
+ * RCX,RDX,R8-R11 - SEAMCALL Leaf specific output registers.
+ *
+ *-------------------------------------------------------------------------
+ *
+ * __seamcall() function ABI:
+ *
+ * @fn (RDI) - SEAMCALL Leaf number, moved to RAX
+ * @rcx (RSI) - Input parameter 1, moved to RCX
+ * @rdx (RDX) - Input parameter 2, moved to RDX
+ * @r8 (RCX) - Input parameter 3, moved to R8
+ * @r9 (R8) - Input parameter 4, moved to R9
+ *
+ * @out (R9) - struct tdx_module_output pointer
+ * stored temporarily in R12 (not
+ * used by the P-SEAMLDR or the TDX
+ * module). It can be NULL.
+ *
+ * Return (via RAX) the completion status of the SEAMCALL, or
+ * TDX_SEAMCALL_VMFAILINVALID.
+ */
+SYM_FUNC_START(__seamcall)
+ FRAME_BEGIN
+ TDX_MODULE_CALL host=1
+ FRAME_END
+ RET
+SYM_FUNC_END(__seamcall)
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index 2d91e7120c90..e82713dd5d54 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -12,14 +12,70 @@
#include <linux/init.h>
#include <linux/errno.h>
#include <linux/printk.h>
+#include <linux/smp.h>
#include <asm/msr-index.h>
#include <asm/msr.h>
#include <asm/tdx.h>
+#include "tdx.h"

static u32 tdx_global_keyid __ro_after_init;
static u32 tdx_guest_keyid_start __ro_after_init;
static u32 tdx_nr_guest_keyids __ro_after_init;

+/*
+ * Wrapper of __seamcall() to convert SEAMCALL leaf function error code
+ * to kernel error code. @seamcall_ret and @out contain the SEAMCALL
+ * leaf function return code and the additional output respectively if
+ * not NULL.
+ */
+static int __always_unused seamcall(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
+ u64 *seamcall_ret,
+ struct tdx_module_output *out)
+{
+ int cpu, ret = 0;
+ u64 sret;
+
+ /* Need a stable CPU id for printing error message */
+ cpu = get_cpu();
+
+ sret = __seamcall(fn, rcx, rdx, r8, r9, out);
+
+ /* Save SEAMCALL return code if the caller wants it */
+ if (seamcall_ret)
+ *seamcall_ret = sret;
+
+ /* SEAMCALL was successful */
+ if (!sret)
+ goto out;
+
+ switch (sret) {
+ case TDX_SEAMCALL_GP:
+ pr_err_once("[firmware bug]: TDX is not enabled by BIOS.\n");
+ ret = -ENODEV;
+ break;
+ case TDX_SEAMCALL_VMFAILINVALID:
+ pr_err_once("TDX module is not loaded.\n");
+ ret = -ENODEV;
+ break;
+ case TDX_SEAMCALL_UD:
+ pr_err_once("SEAMCALL failed: CPU %d is not in VMX operation.\n",
+ cpu);
+ ret = -EINVAL;
+ break;
+ default:
+ pr_err_once("SEAMCALL failed: CPU %d: leaf %llu, error 0x%llx.\n",
+ cpu, fn, sret);
+ if (out)
+ pr_err_once("additional output: rcx 0x%llx, rdx 0x%llx, r8 0x%llx, r9 0x%llx, r10 0x%llx, r11 0x%llx.\n",
+ out->rcx, out->rdx, out->r8,
+ out->r9, out->r10, out->r11);
+ ret = -EIO;
+ }
+out:
+ put_cpu();
+ return ret;
+}
+
static int __init record_keyid_partitioning(u32 *tdx_keyid_start,
u32 *nr_tdx_keyids)
{
diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
new file mode 100644
index 000000000000..48ad1a1ba737
--- /dev/null
+++ b/arch/x86/virt/vmx/tdx/tdx.h
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _X86_VIRT_TDX_H
+#define _X86_VIRT_TDX_H
+
+#include <linux/types.h>
+
+struct tdx_module_output;
+u64 __seamcall(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
+ struct tdx_module_output *out);
+#endif
diff --git a/arch/x86/virt/vmx/tdx/tdxcall.S b/arch/x86/virt/vmx/tdx/tdxcall.S
index 49a54356ae99..757b0c34be10 100644
--- a/arch/x86/virt/vmx/tdx/tdxcall.S
+++ b/arch/x86/virt/vmx/tdx/tdxcall.S
@@ -1,6 +1,7 @@
/* SPDX-License-Identifier: GPL-2.0 */
#include <asm/asm-offsets.h>
#include <asm/tdx.h>
+#include <asm/asm.h>

/*
* TDCALL and SEAMCALL are supported in Binutils >= 2.36.
@@ -45,6 +46,7 @@
/* Leave input param 2 in RDX */

.if \host
+1:
seamcall
/*
* SEAMCALL instruction is essentially a VMExit from VMX root
@@ -57,10 +59,23 @@
* This value will never be used as actual SEAMCALL error code as
* it is from the Reserved status code class.
*/
- jnc .Lno_vmfailinvalid
+ jnc .Lseamcall_out
mov $TDX_SEAMCALL_VMFAILINVALID, %rax
-.Lno_vmfailinvalid:
+ jmp .Lseamcall_out
+2:
+ /*
+ * SEAMCALL caused #GP or #UD. By reaching here %eax contains
+ * the trap number. Convert the trap number to the TDX error
+ * code by setting TDX_SW_ERROR to the high 32-bits of %rax.
+ *
+ * Note cannot OR TDX_SW_ERROR directly to %rax as OR instruction
+ * only accepts 32-bit immediate at most.
+ */
+ mov $TDX_SW_ERROR, %r12
+ orq %r12, %rax

+ _ASM_EXTABLE_FAULT(1b, 2b)
+.Lseamcall_out:
.else
tdcall
.endif
--
2.40.1

Next message: Kai Huang: "[PATCH v11 06/20] x86/virt/tdx: Handle SEAMCALL running out of entropy error"
Previous message: Kai Huang: "[PATCH v11 04/20] x86/cpu: Detect TDX partial write machine check erratum"
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Next in thread: Isaku Yamahata: "Re: [PATCH v11 05/20] x86/virt/tdx: Add SEAMCALL infrastructure"
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