powerpc/pseries: Add a char driver for physical-attestation RTAS

JIRA: https://issues.redhat.com/browse/RHEL-101838

commit 86900ab
Author: Haren Myneni <haren@linux.ibm.com>
Date:   Wed Apr 16 15:57:42 2025 -0700

    powerpc/pseries: Add a char driver for physical-attestation RTAS

    The RTAS call ibm,physical-attestation is used to retrieve
    information about the trusted boot state of the firmware and
    hypervisor on the system, and also Trusted Platform Modules (TPM)
    data if the system is TCG 2.0 compliant.

    This RTAS interface expects the caller to define different command
    structs such as RetrieveTPMLog, RetrievePlatformCertificat and etc,
    in a work area with a maximum size of 4K bytes and the response
    buffer will be returned in the same work area.

    The current implementation of this RTAS function is in the user
    space but allocation of the work area is restricted with the system
    lockdown. So this patch implements this RTAS function in the kernel
    and expose to the user space with open/ioctl/read interfaces.

    PAPR (2.13+ 21.3 ibm,physical-attestation) defines RTAS function:
    - Pass the command struct to obtain the response buffer for the
      specific command.
    - This RTAS function is sequence RTAS call and has to issue RTAS
      call multiple times to get the complete response buffer (max 64K).
      The hypervisor expects the first RTAS call with the sequence 1 and
      the subsequent calls with the sequence number returned from the
      previous calls.

    Expose these interfaces to user space with a
    /dev/papr-physical-attestation character device using the following
    programming model:

     int devfd = open("/dev/papr-physical-attestation");
     int fd = ioctl(devfd, PAPR_PHY_ATTEST_IOC_HANDLE,
                          struct papr_phy_attest_io_block);
     - The user space defines the command struct and requests the
       response for any command.
     - Obtain the complete response buffer and returned the buffer as
       blob to the command specific FD.
     size = read(fd, buf, len);
     - Can retrieve the response buffer once or multiple times until the
       end of BLOB buffer.

    Implemented this new kernel ABI support in librtas library for
    system lockdown

    Signed-off-by: Haren Myneni <haren@linux.ibm.com>
    Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
    Link: https://patch.msgid.link/20250416225743.596462-8-haren@linux.ibm.com

Signed-off-by: Mamatha Inamdar <minamdar@redhat.com>

Author: Mamatha Inamdar

Documentation/userspace-api/ioctl/ioctl-number.rst

@@ -354,6 +354,8 @@ Code  Seq#    Include File                                           Comments
                                                                      <mailto:linuxppc-dev>
 0xB2  06-07 arch/powerpc/include/uapi/asm/papr-platform-dump.h       powerpc/pseries Platform Dump API
                                                                      <mailto:linuxppc-dev>
+0xB2  08  arch/powerpc/include/uapi/asm/papr-physical-attestation.h  powerpc/pseries Physical Attestation API
+                                                                     <mailto:linuxppc-dev>
 0xB3  00     linux/mmc/ioctl.h
 0xB4  00-0F  linux/gpio.h                                            <mailto:linux-gpio@vger.kernel.org>
 0xB5  00-0F  uapi/linux/rpmsg.h                                      <mailto:linux-remoteproc@vger.kernel.org>

arch/powerpc/include/asm/rtas.h

@@ -340,6 +340,7 @@ extern struct mutex rtas_ibm_get_vpd_lock;
 extern struct mutex rtas_ibm_get_indices_lock;
 extern struct mutex rtas_ibm_set_dynamic_indicator_lock;
 extern struct mutex rtas_ibm_get_dynamic_sensor_state_lock;
+extern struct mutex rtas_ibm_physical_attestation_lock;
 
 #define GLOBAL_INTERRUPT_QUEUE 9005
 

arch/powerpc/include/uapi/asm/papr-physical-attestation.h

@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_PAPR_PHYSICAL_ATTESTATION_H_
+#define _UAPI_PAPR_PHYSICAL_ATTESTATION_H_
+
+#include <linux/types.h>
+#include <asm/ioctl.h>
+#include <asm/papr-miscdev.h>
+
+#define PAPR_PHYATTEST_MAX_INPUT 4084 /* Max 4K buffer: 4K-12 */
+
+/*
+ * Defined in PAPR 2.13+ 21.6 Attestation Command Structures.
+ * User space pass this struct and the max size should be 4K.
+ */
+struct papr_phy_attest_io_block {
+	__u8 version;
+	__u8 command;
+	__u8 TCG_major_ver;
+	__u8 TCG_minor_ver;
+	__be32 length;
+	__be32 correlator;
+	__u8 payload[PAPR_PHYATTEST_MAX_INPUT];
+};
+
+/*
+ * ioctl for /dev/papr-physical-attestation. Returns a attestation
+ * command fd handle
+ */
+#define PAPR_PHY_ATTEST_IOC_HANDLE _IOW(PAPR_MISCDEV_IOC_ID, 8, struct papr_phy_attest_io_block)
+
+#endif /* _UAPI_PAPR_PHYSICAL_ATTESTATION_H_ */

arch/powerpc/kernel/rtas.c

@@ -76,6 +76,7 @@ unsigned long rtas_rmo_buf;
 void (*rtas_flash_term_hook)(int);
 EXPORT_SYMBOL(rtas_flash_term_hook);
 
+DEFINE_MUTEX(rtas_ibm_physical_attestation_lock);
 DEFINE_MUTEX(rtas_ibm_get_vpd_lock);
 DEFINE_MUTEX(rtas_ibm_get_indices_lock);
 DEFINE_MUTEX(rtas_ibm_set_dynamic_indicator_lock);
@@ -1130,6 +1131,9 @@ static struct mutex *find_rtas_mutex(int token)
 	if (token == rtas_token("ibm,get-dynamic-sensor-state"))
 		return &rtas_ibm_get_dynamic_sensor_state_lock;
 
+	if (token == rtas_token("ibm,physical-attestation"))
+		return &rtas_ibm_physical_attestation_lock;
+
 	return NULL;
 }
 

arch/powerpc/platforms/pseries/Makefile

@@ -5,7 +5,7 @@ ccflags-$(CONFIG_PPC_PSERIES_DEBUG)	+= -DDEBUG
 obj-y			:= lpar.o hvCall.o nvram.o reconfig.o \
 			   of_helpers.o rtas-work-area.o papr-sysparm.o \
 			   papr-rtas-common.o papr-vpd.o papr-indices.o \
-			   papr-platform-dump.o \
+			   papr-platform-dump.o papr-phy-attest.o \
 			   setup.o iommu.o event_sources.o ras.o \
 			   firmware.o power.o dlpar.o mobility.o rng.o \
 			   pci.o pci_dlpar.o eeh_pseries.o msi.o \

arch/powerpc/platforms/pseries/papr-phy-attest.c

@@ -0,0 +1,288 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#define pr_fmt(fmt) "papr-phy-attest: " fmt
+
+#include <linux/build_bug.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/lockdep.h>
+#include <linux/kernel.h>
+#include <linux/miscdevice.h>
+#include <linux/signal.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/string_helpers.h>
+#include <linux/uaccess.h>
+#include <asm/machdep.h>
+#include <asm/rtas-work-area.h>
+#include <asm/rtas.h>
+#include <uapi/asm/papr-physical-attestation.h>
+#include "papr-rtas-common.h"
+
+/**
+ * struct rtas_phy_attest_params - Parameters (in and out) for
+ * ibm,physical-attestation.
+ *
+ * @cmd:  In: Caller-provided attestation command buffer. Must be
+ *        RTAS-addressable.
+ * @work_area: In: Caller-provided work area buffer for attestation
+ *             command structure
+ *             Out: Caller-provided work area buffer for the response
+ * @cmd_len:   In: Caller-provided attestation command structure
+ *             length
+ * @sequence:  In: Sequence number. Out: Next sequence number.
+ * @written:   Out: Bytes written by ibm,physical-attestation to
+ *             @work_area.
+ * @status:    Out: RTAS call status.
+ */
+struct rtas_phy_attest_params {
+	struct papr_phy_attest_io_block cmd;
+	struct rtas_work_area *work_area;
+	u32 cmd_len;
+	u32 sequence;
+	u32 written;
+	s32 status;
+};
+
+/**
+ * rtas_physical_attestation() - Call ibm,physical-attestation to
+ * fill a work area buffer.
+ * @params: See &struct rtas_phy_attest_params.
+ *
+ * Calls ibm,physical-attestation until it errors or successfully
+ * deposits data into the supplied work area. Handles RTAS retry
+ * statuses. Maps RTAS error statuses to reasonable errno values.
+ *
+ * The caller is expected to invoke rtas_physical_attestation()
+ * multiple times to retrieve all the data for the provided
+ * attestation command. Only one sequence should be in progress at
+ * any time; starting a new sequence will disrupt any sequence
+ * already in progress. Serialization of attestation retrieval
+ * sequences is the responsibility of the caller.
+ *
+ * The caller should inspect @params.status to determine whether more
+ * calls are needed to complete the sequence.
+ *
+ * Context: May sleep.
+ * Return: -ve on error, 0 otherwise.
+ */
+static int rtas_physical_attestation(struct rtas_phy_attest_params *params)
+{
+	struct rtas_work_area *work_area;
+	s32 fwrc, token;
+	u32 rets[2];
+	int ret;
+
+	work_area = params->work_area;
+	token = rtas_token("ibm,physical-attestation");
+	if (token == RTAS_UNKNOWN_SERVICE)
+		return -ENOENT;
+
+	lockdep_assert_held(&rtas_ibm_physical_attestation_lock);
+
+	do {
+		fwrc = rtas_call(token, 3, 3, rets,
+				 rtas_work_area_phys(work_area),
+				 params->cmd_len,
+				 params->sequence);
+	} while (rtas_busy_delay(fwrc));
+
+	switch (fwrc) {
+	case RTAS_HARDWARE_ERROR:
+		ret = -EIO;
+		break;
+	case RTAS_INVALID_PARAMETER:
+		ret = -EINVAL;
+		break;
+	case RTAS_SEQ_MORE_DATA:
+		params->sequence = rets[0];
+		fallthrough;
+	case RTAS_SEQ_COMPLETE:
+		params->written = rets[1];
+		/*
+		 * Kernel or firmware bug, do not continue.
+		 */
+		if (WARN(params->written > rtas_work_area_size(work_area),
+			 "possible write beyond end of work area"))
+			ret = -EFAULT;
+		else
+			ret = 0;
+		break;
+	default:
+		ret = -EIO;
+		pr_err_ratelimited("unexpected ibm,get-phy_attest status %d\n", fwrc);
+		break;
+	}
+
+	params->status = fwrc;
+	return ret;
+}
+
+/*
+ * Internal physical-attestation sequence APIs. A physical-attestation
+ * sequence is a series of calls to get ibm,physical-attestation
+ * for a given attestation command. The sequence ends when an error
+ * is encountered or all data for the attestation command has been
+ * returned.
+ */
+
+/**
+ * phy_attest_sequence_begin() - Begin a response data for attestation
+ * command retrieval sequence.
+ * @seq: user specified parameters for RTAS call from seq struct.
+ *
+ * Context: May sleep.
+ */
+static void phy_attest_sequence_begin(struct papr_rtas_sequence *seq)
+{
+	struct rtas_phy_attest_params *param;
+
+	/*
+	 * We could allocate the work area before acquiring the
+	 * function lock, but that would allow concurrent requests to
+	 * exhaust the limited work area pool for no benefit. So
+	 * allocate the work area under the lock.
+	 */
+	mutex_lock(&rtas_ibm_physical_attestation_lock);
+	param =  (struct rtas_phy_attest_params *)seq->params;
+	param->work_area = rtas_work_area_alloc(SZ_4K);
+	memcpy(rtas_work_area_raw_buf(param->work_area), &param->cmd,
+			param->cmd_len);
+	param->sequence = 1;
+	param->status = 0;
+}
+
+/**
+ * phy_attest_sequence_end() - Finalize a attestation command
+ * response retrieval sequence.
+ * @seq: Sequence state.
+ *
+ * Releases resources obtained by phy_attest_sequence_begin().
+ */
+static void phy_attest_sequence_end(struct papr_rtas_sequence *seq)
+{
+	struct rtas_phy_attest_params *param;
+
+	param =  (struct rtas_phy_attest_params *)seq->params;
+	rtas_work_area_free(param->work_area);
+	mutex_unlock(&rtas_ibm_physical_attestation_lock);
+	kfree(param);
+}
+
+/*
+ * Generator function to be passed to papr_rtas_blob_generate().
+ */
+static const char *phy_attest_sequence_fill_work_area(struct papr_rtas_sequence *seq,
+						size_t *len)
+{
+	struct rtas_phy_attest_params *p;
+	bool init_state;
+
+	p = (struct rtas_phy_attest_params *)seq->params;
+	init_state = (p->written == 0) ? true : false;
+
+	if (papr_rtas_sequence_should_stop(seq, p->status, init_state))
+		return NULL;
+	if (papr_rtas_sequence_set_err(seq, rtas_physical_attestation(p)))
+		return NULL;
+	*len = p->written;
+	return rtas_work_area_raw_buf(p->work_area);
+}
+
+static const struct file_operations papr_phy_attest_handle_ops = {
+	.read = papr_rtas_common_handle_read,
+	.llseek = papr_rtas_common_handle_seek,
+	.release = papr_rtas_common_handle_release,
+};
+
+/**
+ * papr_phy_attest_create_handle() - Create a fd-based handle for
+ * reading the response for the given attestation command.
+ * @ulc: Attestation command in user memory; defines the scope of
+ *       data for the attestation command to retrieve.
+ *
+ * Handler for PAPR_PHYSICAL_ATTESTATION_IOC_CREATE_HANDLE ioctl
+ * command. Validates @ulc and instantiates an immutable response
+ * "blob" for attestation command. The blob is attached to a file
+ * descriptor for reading by user space. The memory backing the blob
+ * is freed when the file is released.
+ *
+ * The entire requested response buffer for the attestation command
+ * retrieved by this call and all necessary RTAS interactions are
+ * performed before returning the fd to user space. This keeps the
+ * read handler simple and ensures that kernel can prevent
+ * interleaving ibm,physical-attestation call sequences.
+ *
+ * Return: The installed fd number if successful, -ve errno otherwise.
+ */
+static long papr_phy_attest_create_handle(struct papr_phy_attest_io_block __user *ulc)
+{
+	struct rtas_phy_attest_params *params;
+	struct papr_rtas_sequence seq = {};
+	int fd;
+
+	/*
+	 * Freed in phy_attest_sequence_end().
+	 */
+	params =  kzalloc(sizeof(*params), GFP_KERNEL_ACCOUNT);
+	if (!params)
+		return -ENOMEM;
+
+	if (copy_from_user(&params->cmd, ulc,
+			sizeof(struct papr_phy_attest_io_block)))
+		return -EFAULT;
+
+	params->cmd_len = be32_to_cpu(params->cmd.length);
+	seq = (struct papr_rtas_sequence) {
+		.begin = phy_attest_sequence_begin,
+		.end = phy_attest_sequence_end,
+		.work = phy_attest_sequence_fill_work_area,
+	};
+
+	seq.params = (void *)params;
+
+	fd = papr_rtas_setup_file_interface(&seq,
+			&papr_phy_attest_handle_ops,
+			"[papr-physical-attestation]");
+
+	return fd;
+}
+
+/*
+ * Top-level ioctl handler for /dev/papr-physical-attestation.
+ */
+static long papr_phy_attest_dev_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
+{
+	void __user *argp = (__force void __user *)arg;
+	long ret;
+
+	switch (ioctl) {
+	case PAPR_PHY_ATTEST_IOC_HANDLE:
+		ret = papr_phy_attest_create_handle(argp);
+		break;
+	default:
+		ret = -ENOIOCTLCMD;
+		break;
+	}
+	return ret;
+}
+
+static const struct file_operations papr_phy_attest_ops = {
+	.unlocked_ioctl = papr_phy_attest_dev_ioctl,
+};
+
+static struct miscdevice papr_phy_attest_dev = {
+	.minor = MISC_DYNAMIC_MINOR,
+	.name = "papr-physical-attestation",
+	.fops = &papr_phy_attest_ops,
+};
+
+static __init int papr_phy_attest_init(void)
+{
+	if (!rtas_service_present("ibm,physical-attestation"))
+		return -ENODEV;
+
+	return misc_register(&papr_phy_attest_dev);
+}
+machine_device_initcall(pseries, papr_phy_attest_init);