cpu/x86/smm: reserve SMRAM for OPAL S3 state

Reserve a small persistent SMRAM subregion for OPAL S3 unlock state, so
the payload-provided OPAL secret can survive SMM handler reload on S3
resume.

Expose the region base/size to SMM via smm_runtime and provide an
accessor for SMM code. Clear the region on cold boot/reboot, but
preserve it when waking from S3.

TEST=tested with rest of patch train

Change-Id: Ib1e92edb31c845367afe6185e5fa18ab1bc71108
Signed-off-by: Sean Rhodes <sean@starlabs.systems>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/91414
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/cpu/x86/Kconfig

@@ -196,6 +196,21 @@ config SMM_MODULE_STACK_SIZE
 	  This option determines the size of the stack within the SMM handler
 	  modules.
 
+config SMM_OPAL_S3_STATE_SMRAM
+	bool
+	help
+	  Reserve a small persistent region in SMRAM for OPAL S3 state so the
+	  OPAL secret survives SMM handler reload on S3 resume.
+
+config SMM_OPAL_S3_STATE_SMRAM_SIZE
+	hex
+	default 0x1000 if SMM_OPAL_S3_STATE_SMRAM
+	default 0x0
+	help
+	  Size in bytes of the persistent SMRAM region reserved for OPAL S3
+	  secret/state. Must be large enough to store the OPAL S3 state
+	  structure and should be kept minimal to reduce SMRAM pressure.
+
 config SMM_OPAL_S3_SCRATCH_CBMEM
 	bool
 	depends on HAVE_ACPI_RESUME

src/cpu/x86/smm/smm_module_handler.c

@@ -74,6 +74,14 @@ void smm_get_opal_s3_scratch_buffer(uintptr_t *base, size_t *size)
 }
 #endif
 
+#if CONFIG(SMM_OPAL_S3_STATE_SMRAM)
+void smm_get_opal_s3_state_buffer(uintptr_t *base, size_t *size)
+{
+	*base = smm_runtime.opal_s3_state_base;
+	*size = smm_runtime.opal_s3_state_size;
+}
+#endif
+
 void smm_get_cbmemc_buffer(void **buffer_out, size_t *size_out)
 {
 	*buffer_out = smm_runtime.cbmemc;

src/cpu/x86/smm/smm_module_loader.c

@@ -1,5 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
+#include <acpi/acpi.h>
 #include <acpi/acpi_gnvs.h>
 #include <cbmem.h>
 #include <commonlib/helpers.h>
@@ -386,6 +387,23 @@ static void setup_smihandler_params(struct smm_runtime *mod_params,
 		mod_params->opal_s3_scratch_size = opal_s3_scratch_size;
 	}
 #endif
+
+#if CONFIG(SMM_OPAL_S3_STATE_SMRAM)
+	uintptr_t state_base = 0;
+	size_t state_size = 0;
+	if (smm_subregion(SMM_SUBREGION_OPAL_S3_STATE, &state_base, &state_size)) {
+		printk(BIOS_ERR, "SMM: Failed to locate OPAL S3 state SMRAM region\n");
+		mod_params->opal_s3_state_base = 0;
+		mod_params->opal_s3_state_size = 0;
+	} else {
+		mod_params->opal_s3_state_base = state_base;
+		mod_params->opal_s3_state_size = state_size;
+
+		/* Clear any stale state on cold boot/reboot, but preserve it on S3 resume. */
+		if (!acpi_is_wakeup_s3())
+			memset((void *)state_base, 0, state_size);
+	}
+#endif
 }
 
 static void print_region(const char *name, const struct region region)

src/cpu/x86/smm/tseg_region.c

@@ -15,6 +15,8 @@
  *     +-------------------------+
  *     |  External Stage Cache   | SMM_RESERVED_SIZE
  *     +-------------------------+
+ *     |   OPAL S3 State (opt)   | SMM_OPAL_S3_STATE_SMRAM_SIZE
+ *     +-------------------------+
  *     |      code and data      |
  *     |         (TSEG)          |
  *     +-------------------------+ TSEG
@@ -25,6 +27,7 @@ int smm_subregion(int sub, uintptr_t *start, size_t *size)
 	size_t sub_size;
 	const size_t ied_size = CONFIG_IED_REGION_SIZE;
 	const size_t cache_size = CONFIG_SMM_RESERVED_SIZE;
+	const size_t opal_state_size = CONFIG_SMM_OPAL_S3_STATE_SMRAM_SIZE;
 
 	if (CONFIG(SMM_TSEG))
 		smm_region(&sub_base, &sub_size);
@@ -34,13 +37,21 @@ int smm_subregion(int sub, uintptr_t *start, size_t *size)
 		return -1;
 
 	ASSERT(IS_ALIGNED(sub_base, sub_size));
-	ASSERT(sub_size > (cache_size + ied_size));
+	ASSERT(sub_size > (cache_size + ied_size + opal_state_size));
 
 	switch (sub) {
 	case SMM_SUBREGION_HANDLER:
 		/* Handler starts at the base of TSEG. */
 		sub_size -= ied_size;
 		sub_size -= cache_size;
+		sub_size -= opal_state_size;
+		break;
+	case SMM_SUBREGION_OPAL_S3_STATE:
+		if (!opal_state_size)
+			return -1;
+		/* Persistent OPAL S3 state lives below the external stage cache. */
+		sub_base += sub_size - (ied_size + cache_size + opal_state_size);
+		sub_size = opal_state_size;
 		break;
 	case SMM_SUBREGION_CACHE:
 		/* External cache is in the middle of TSEG. */

src/include/cpu/x86/smm.h

@@ -100,6 +100,10 @@ struct smm_runtime {
 	uintptr_t opal_s3_scratch_base;
 	size_t opal_s3_scratch_size;
 #endif
+#if CONFIG(SMM_OPAL_S3_STATE_SMRAM)
+	uintptr_t opal_s3_state_base;
+	size_t opal_s3_state_size;
+#endif
 } __packed;
 
 struct smm_module_params {
@@ -206,6 +210,8 @@ static inline void aseg_region(uintptr_t *start, size_t *size)
 enum {
 	/* SMM handler area. */
 	SMM_SUBREGION_HANDLER,
+	/* Persistent OPAL S3 state area. */
+	SMM_SUBREGION_OPAL_S3_STATE,
 	/* SMM cache region. */
 	SMM_SUBREGION_CACHE,
 	/* Chipset specific area. */
@@ -245,5 +251,8 @@ void smm_get_smmstore_com_buffer(uintptr_t *base, size_t *size);
 #if CONFIG(SMM_OPAL_S3_SCRATCH_CBMEM)
 void smm_get_opal_s3_scratch_buffer(uintptr_t *base, size_t *size);
 #endif
+#if CONFIG(SMM_OPAL_S3_STATE_SMRAM)
+void smm_get_opal_s3_state_buffer(uintptr_t *base, size_t *size);
+#endif
 
 #endif /* CPU_X86_SMM_H */