A module update request is a struct used to describe information about
the TDX module to install. It is part of the P-SEAMLDR <-> kernel ABI
and is accepted by the SEAMLDR_INSTALL SEAMCALL.

The request includes pointers to pages that contain the module binary, a
pointer to a sigstruct file, and an update scenario.

Define the request struct according to the P-SEAMLDR spec [1], and parse
the bitstream from userspace to populate that struct for later module
updates.

Note that the bitstream format is specified in [2]. It consists of a
header, a sigstruct, a module binary, and reserved fields for future
extensions. The header includes fields like a simple checksum and a
signature for error detection.

Signed-off-by: Chao Gao <chao.gao@intel.com>
Tested-by: Farrah Chen <farrah.chen@intel.com>
Link: https://cdrdv2.intel.com/v1/dl/getContent/733584 # [1]
Link: https://github.com/intel/tdx-module-binaries/blob/main/blob_structure.txt # [2]
---
v2:
 - Add a high level description of the bitstream in changelog
 - Document where the bitstream format is defined in comments
 - Add checks for the version and reserved fields in tdx_blob
---
 arch/x86/virt/vmx/tdx/seamldr.c | 155 ++++++++++++++++++++++++++++++++
 1 file changed, 155 insertions(+)

diff --git a/arch/x86/virt/vmx/tdx/seamldr.c b/arch/x86/virt/vmx/tdx/seamldr.c
index 9f7d96ca8b2f..00a01acc15fd 100644
--- a/arch/x86/virt/vmx/tdx/seamldr.c
+++ b/arch/x86/virt/vmx/tdx/seamldr.c
@@ -6,9 +6,12 @@
  */
 #define pr_fmt(fmt)	"seamldr: " fmt
 
+#include <linux/cleanup.h>
 #include <linux/cpuhplock.h>
 #include <linux/cpumask.h>
 #include <linux/irqflags.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
 #include <linux/types.h>
 
 #include <asm/seamldr.h>
@@ -18,6 +21,26 @@
 /* P-SEAMLDR SEAMCALL leaf function */
 #define P_SEAMLDR_INFO			0x8000000000000000
 
+/* P-SEAMLDR can accept up to 496 4KB pages for TDX module binary */
+#define SEAMLDR_MAX_NR_MODULE_4KB_PAGES	496
+
+/* scenario field in struct seamldr_params */
+#define SEAMLDR_SCENARIO_UPDATE		1
+
+/*
+ * Passed to P-SEAMLDR to describe information about the TDX module to install.
+ * Defined in "SEAM Loader (SEAMLDR) Interface Specification", Revision
+ * 343755-003, Section 3.2.
+ */
+struct seamldr_params {
+	u32	version;
+	u32	scenario;
+	u64	sigstruct_pa;
+	u8	reserved[104];
+	u64	num_module_pages;
+	u64	mod_pages_pa_list[SEAMLDR_MAX_NR_MODULE_4KB_PAGES];
+} __packed;
+
 static struct seamldr_info seamldr_info __aligned(256);
 
 static inline int seamldr_call(u64 fn, struct tdx_module_args *args)
@@ -72,6 +95,133 @@ const struct seamldr_info *seamldr_get_info(void)
 }
 EXPORT_SYMBOL_GPL_FOR_MODULES(seamldr_get_info, "tdx-host");
 
+static void free_seamldr_params(struct seamldr_params *params)
+{
+	free_page((unsigned long)params);
+}
+
+/* Allocate and populate a seamldr_params */
+static struct seamldr_params *alloc_seamldr_params(const void *module, int module_size,
+						   const void *sig, int sig_size)
+{
+	struct seamldr_params *params;
+	const u8 *ptr;
+	int i;
+
+	BUILD_BUG_ON(sizeof(struct seamldr_params) != SZ_4K);
+	if (module_size > SEAMLDR_MAX_NR_MODULE_4KB_PAGES * SZ_4K)
+		return ERR_PTR(-EINVAL);
+
+	if (!IS_ALIGNED(module_size, SZ_4K) || !IS_ALIGNED(sig_size, SZ_4K) ||
+	    !IS_ALIGNED((unsigned long)module, SZ_4K) ||
+	    !IS_ALIGNED((unsigned long)sig, SZ_4K))
+		return ERR_PTR(-EINVAL);
+
+	/* seamldr_params accepts one 4KB-page for sigstruct */
+	if (sig_size != SZ_4K)
+		return ERR_PTR(-EINVAL);
+
+	params = (struct seamldr_params *)get_zeroed_page(GFP_KERNEL);
+	if (!params)
+		return ERR_PTR(-ENOMEM);
+
+	params->scenario = SEAMLDR_SCENARIO_UPDATE;
+	params->sigstruct_pa = (vmalloc_to_pfn(sig) << PAGE_SHIFT) +
+			       ((unsigned long)sig & ~PAGE_MASK);
+	params->num_module_pages = module_size / SZ_4K;
+
+	ptr = module;
+	for (i = 0; i < params->num_module_pages; i++) {
+		params->mod_pages_pa_list[i] = (vmalloc_to_pfn(ptr) << PAGE_SHIFT) +
+					       ((unsigned long)ptr & ~PAGE_MASK);
+		ptr += SZ_4K;
+	}
+
+	return params;
+}
+
+/*
+ * Intel TDX Module blob. Its format is defined at:
+ * https://github.com/intel/tdx-module-binaries/blob/main/blob_structure.txt
+ */
+struct tdx_blob {
+	u16	version;
+	u16	checksum;
+	u32	offset_of_module;
+	u8	signature[8];
+	u32	len;
+	u32	resv1;
+	u64	resv2[509];
+	u8	data[];
+} __packed;
+
+/*
+ * Verify that the checksum of the entire blob is zero. The checksum is
+ * calculated by summing up all 16-bit words, with carry bits dropped.
+ */
+static bool verify_checksum(const struct tdx_blob *blob)
+{
+	u32 size = blob->len;
+	u16 checksum = 0;
+	const u16 *p;
+	int i;
+
+	/* Handle the last byte if the size is odd */
+	if (size % 2) {
+		checksum += *((const u8 *)blob + size - 1);
+		size--;
+	}
+
+	p = (const u16 *)blob;
+	for (i = 0; i < size; i += 2) {
+		checksum += *p;
+		p++;
+	}
+
+	return !checksum;
+}
+
+static struct seamldr_params *init_seamldr_params(const u8 *data, u32 size)
+{
+	const struct tdx_blob *blob = (const void *)data;
+	int module_size, sig_size;
+	const void *sig, *module;
+
+	if (blob->version != 0x100) {
+		pr_err("unsupported blob version: %u\n", blob->version);
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (blob->resv1 || memchr_inv(blob->resv2, 0, sizeof(blob->resv2))) {
+		pr_err("non-zero reserved fields\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	/* Split the given blob into a sigstruct and a module */
+	sig		= blob->data;
+	sig_size	= blob->offset_of_module - sizeof(struct tdx_blob);
+	module		= data + blob->offset_of_module;
+	module_size	= size - blob->offset_of_module;
+
+	if (sig_size <= 0 || module_size <= 0 || blob->len != size)
+		return ERR_PTR(-EINVAL);
+
+	if (memcmp(blob->signature, "TDX-BLOB", 8)) {
+		pr_err("invalid signature\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (!verify_checksum(blob)) {
+		pr_err("invalid checksum\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	return alloc_seamldr_params(module, module_size, sig, sig_size);
+}
+
+DEFINE_FREE(free_seamldr_params, struct seamldr_params *,
+	    if (!IS_ERR_OR_NULL(_T)) free_seamldr_params(_T))
+
 int seamldr_install_module(const u8 *data, u32 size)
 {
 	const struct seamldr_info *info = seamldr_get_info();
@@ -82,6 +232,11 @@ int seamldr_install_module(const u8 *data, u32 size)
 	if (!info->num_remaining_updates)
 		return -ENOSPC;
 
+	struct seamldr_params *params __free(free_seamldr_params) =
+						init_seamldr_params(data, size);
+	if (IS_ERR(params))
+		return PTR_ERR(params);
+
 	guard(cpus_read_lock)();
 	if (!cpumask_equal(cpu_online_mask, cpu_present_mask)) {
 		pr_err("Cannot update TDX module if any CPU is offline\n");
-- 
2.47.3