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[PATCH v5 1/4] firmware: introduce sysfs driver for QEMU's fw_cfg device

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  [PATCH v5 1/4] firmware: introduce sysfs driver for QEMU's fw_cfg device "Gabriel L. Somlo" <somlo@cmu.edu> - 2015-11-23 17:00 +0100
    Re: [PATCH v5 1/4] firmware: introduce sysfs driver for QEMU's  fw_cfg device "Gabriel L. Somlo" <somlo@cmu.edu> - 2015-11-24 18:00 +0100
      Re: [Qemu-devel] [PATCH v5 1/4] firmware: introduce sysfs driver for  QEMU's fw_cfg device Eric Blake <eblake@redhat.com> - 2015-11-24 18:40 +0100
        Re: [Qemu-devel] [PATCH v5 1/4] firmware: introduce sysfs driver for  QEMU's fw_cfg device Laszlo Ersek <lersek@redhat.com> - 2015-11-24 18:50 +0100
        Re: [Qemu-devel] [PATCH v5 1/4] firmware: introduce sysfs driver for  QEMU's fw_cfg device "Gabriel L. Somlo" <somlo@cmu.edu> - 2015-11-24 19:20 +0100

#1275503 — [PATCH v5 1/4] firmware: introduce sysfs driver for QEMU's fw_cfg device

From: Gabriel Somlo <somlo@cmu.edu>

Make fw_cfg entries of type "file" available via sysfs. Entries
are listed under /sys/firmware/qemu_fw_cfg/by_key, in folders
named after each entry's selector key. Filename, selector value,
and size read-only attributes are included for each entry. Also,
a "raw" attribute allows retrieval of the full binary content of
each entry.

The fw_cfg device can be instantiated automatically from ACPI or
the Device Tree, or manually by using a kernel module (or command
line) parameter, with a syntax outlined in the documentation file.

Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
---
 .../ABI/testing/sysfs-firmware-qemu_fw_cfg         |  58 ++
 drivers/firmware/Kconfig                           |  19 +
 drivers/firmware/Makefile                          |   1 +
 drivers/firmware/qemu_fw_cfg.c                     | 611 +++++++++++++++++++++
 4 files changed, 689 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
 create mode 100644 drivers/firmware/qemu_fw_cfg.c

diff --git a/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg b/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
new file mode 100644
index 0000000..718fbac
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
@@ -0,0 +1,58 @@
+What:		/sys/firmware/qemu_fw_cfg/
+Date:		August 2015
+Contact:	Gabriel Somlo <somlo@cmu.edu>
+Description:
+		Several different architectures supported by QEMU (x86, arm,
+		sun4*, ppc/mac) are provisioned with a firmware configuration
+		(fw_cfg) device, originally intended as a way for the host to
+		provide configuration data to the guest firmware. Starting
+		with QEMU v2.4, arbitrary fw_cfg file entries may be specified
+		by the user on the command line, which makes fw_cfg additionally
+		useful as an out-of-band, asynchronous mechanism for providing
+		configuration data to the guest userspace.
+
+		The authoritative guest-side hardware interface documentation
+		to the fw_cfg device ca be found in "docs/specs/fw_cfg.txt" in
+		the QEMU source tree.
+
+		=== SysFS fw_cfg Interface ===
+
+		The fw_cfg sysfs interface described in this document is only
+		intended to display discoverable blobs (i.e., those registered
+		with the file directory), as there is no way to determine the
+		presence or size of "legacy" blobs (with selector keys between
+		0x0002 and 0x0018) programmatically.
+
+		All fw_cfg information is shown under:
+
+			/sys/firmware/qemu_fw_cfg/
+
+		The only legacy blob displayed is the fw_cfg device revision:
+
+			/sys/firmware/qemu_fw_cfg/rev
+
+		--- Discoverable fw_cfg blobs by selector key ---
+
+		All discoverable blobs listed in the fw_cfg file directory are
+		displayed as entries named after their unique selector key
+		value, e.g.:
+
+			/sys/firmware/qemu_fw_cfg/by_key/32
+			/sys/firmware/qemu_fw_cfg/by_key/33
+			/sys/firmware/qemu_fw_cfg/by_key/34
+			...
+
+		Each such fw_cfg sysfs entry has the following values exported
+		as attributes:
+
+		name  	: The 56-byte nul-terminated ASCII string used as the
+			  blob's 'file name' in the fw_cfg directory.
+		size  	: The length of the blob, as given in the fw_cfg
+			  directory.
+		key	: The value of the blob's selector key as given in the
+			  fw_cfg directory. This value is the same as used in
+			  the parent directory name.
+		raw	: The raw bytes of the blob, obtained by selecting the
+			  entry via the control register, and reading a number
+			  of bytes equal to the blob size from the data
+			  register.
diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
index cf478fe..3cf920a 100644
--- a/drivers/firmware/Kconfig
+++ b/drivers/firmware/Kconfig
@@ -161,6 +161,25 @@ config RASPBERRYPI_FIRMWARE
 	  This option enables support for communicating with the firmware on the
 	  Raspberry Pi.
 
+config FW_CFG_SYSFS
+	tristate "QEMU fw_cfg device support in sysfs"
+	depends on SYSFS
+	default n
+	help
+	  Say Y or M here to enable the exporting of the QEMU firmware
+	  configuration (fw_cfg) file entries via sysfs. Entries are
+	  found under /sys/firmware/fw_cfg when this option is enabled
+	  and loaded.
+
+config FW_CFG_SYSFS_CMDLINE
+	bool "QEMU fw_cfg device parameter parsing"
+	depends on FW_CFG_SYSFS
+	help
+	  Allow the qemu_fw_cfg device to be initialized via the kernel
+	  command line or using a module parameter.
+	  WARNING: Using incorrect parameters (base address in particular)
+	  may crash your system.
+
 config QCOM_SCM
 	bool
 	depends on ARM || ARM64
diff --git a/drivers/firmware/Makefile b/drivers/firmware/Makefile
index 48dd417..474bada 100644
--- a/drivers/firmware/Makefile
+++ b/drivers/firmware/Makefile
@@ -14,6 +14,7 @@ obj-$(CONFIG_ISCSI_IBFT_FIND)	+= iscsi_ibft_find.o
 obj-$(CONFIG_ISCSI_IBFT)	+= iscsi_ibft.o
 obj-$(CONFIG_FIRMWARE_MEMMAP)	+= memmap.o
 obj-$(CONFIG_RASPBERRYPI_FIRMWARE) += raspberrypi.o
+obj-$(CONFIG_FW_CFG_SYSFS)	+= qemu_fw_cfg.o
 obj-$(CONFIG_QCOM_SCM)		+= qcom_scm.o
 obj-$(CONFIG_QCOM_SCM_64)	+= qcom_scm-64.o
 obj-$(CONFIG_QCOM_SCM_32)	+= qcom_scm-32.o
diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
new file mode 100644
index 0000000..618304a
--- /dev/null
+++ b/drivers/firmware/qemu_fw_cfg.c
@@ -0,0 +1,611 @@
+/*
+ * drivers/firmware/qemu_fw_cfg.c
+ *
+ * Copyright 2015 Carnegie Mellon University
+ *
+ * Expose entries from QEMU's firmware configuration (fw_cfg) device in
+ * sysfs (read-only, under "/sys/firmware/qemu_fw_cfg/...").
+ *
+ * The fw_cfg device may be instantiated via either an ACPI node (on x86
+ * and select subsets of aarch64), a Device Tree node (on arm), or using
+ * a kernel module (or command line) parameter with the following syntax:
+ *
+ *      [fw_cfg.]ioport=<size>@<base>[:<ctrl_off>:<data_off>]
+ * or
+ *      [fw_cfg.]mmio=<size>@<base>[:<ctrl_off>:<data_off>]
+ *
+ * where:
+ *      <size>     := size of ioport or mmio range
+ *      <base>     := physical base address of ioport or mmio range
+ *      <ctrl_off> := (optional) offset of control register
+ *      <data_off> := (optional) offset of data register
+ *
+ * e.g.:
+ *      fw_cfg.ioport=2@0x510:0:1		(the default on x86)
+ * or
+ *      fw_cfg.mmio=0xA@0x9020000:8:0		(the default on arm)
+ */
+
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/acpi.h>
+#include <linux/slab.h>
+#include <linux/io.h>
+#include <linux/ioport.h>
+
+MODULE_AUTHOR("Gabriel L. Somlo <somlo@cmu.edu>");
+MODULE_DESCRIPTION("QEMU fw_cfg sysfs support");
+MODULE_LICENSE("GPL");
+
+/* selector key values for "well-known" fw_cfg entries */
+#define FW_CFG_SIGNATURE  0x00
+#define FW_CFG_ID         0x01
+#define FW_CFG_FILE_DIR   0x19
+
+/* size in bytes of fw_cfg signature */
+#define FW_CFG_SIG_SIZE 4
+
+/* fw_cfg "file name" is up to 56 characters (including terminating nul) */
+#define FW_CFG_MAX_FILE_PATH 56
+
+/* fw_cfg file directory entry type */
+struct fw_cfg_file {
+	u32 size;
+	u16 select;
+	u16 reserved;
+	char name[FW_CFG_MAX_FILE_PATH];
+};
+
+/* fw_cfg device i/o register addresses */
+static bool fw_cfg_is_mmio;
+static phys_addr_t fw_cfg_p_base;
+static resource_size_t fw_cfg_p_size;
+static void __iomem *fw_cfg_dev_base;
+static void __iomem *fw_cfg_reg_ctrl;
+static void __iomem *fw_cfg_reg_data;
+
+/* atomic access to fw_cfg device (potentially slow i/o, so using mutex) */
+static DEFINE_MUTEX(fw_cfg_dev_lock);
+
+/* pick appropriate endianness for selector key */
+static inline u16 fw_cfg_sel_endianness(u16 key)
+{
+	return fw_cfg_is_mmio ? cpu_to_be16(key) : cpu_to_le16(key);
+}
+
+/* read chunk of given fw_cfg blob (caller responsible for sanity-check) */
+static inline void fw_cfg_read_blob(u16 key,
+				    void *buf, loff_t pos, size_t count)
+{
+	mutex_lock(&fw_cfg_dev_lock);
+	iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
+	while (pos-- > 0)
+		ioread8(fw_cfg_reg_data);
+	ioread8_rep(fw_cfg_reg_data, buf, count);
+	mutex_unlock(&fw_cfg_dev_lock);
+}
+
+/* clean up fw_cfg device i/o */
+static void fw_cfg_io_cleanup(void)
+{
+	if (fw_cfg_is_mmio) {
+		iounmap(fw_cfg_dev_base);
+		release_mem_region(fw_cfg_p_base, fw_cfg_p_size);
+	} else {
+		ioport_unmap(fw_cfg_dev_base);
+		release_region(fw_cfg_p_base, fw_cfg_p_size);
+	}
+}
+
+/* initialize fw_cfg device i/o from platform data */
+static int fw_cfg_do_platform_probe(struct platform_device *pdev)
+{
+	char sig[FW_CFG_SIG_SIZE];
+	struct resource *range, *ctrl, *data;
+
+	/* acquire i/o range details */
+	fw_cfg_is_mmio = false;
+	range = platform_get_resource(pdev, IORESOURCE_IO, 0);
+	if (!range) {
+		fw_cfg_is_mmio = true;
+		range = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+		if (!range)
+			return -EINVAL;
+	}
+	fw_cfg_p_base = range->start;
+	fw_cfg_p_size = resource_size(range);
+
+	if (fw_cfg_is_mmio) {
+		if (!request_mem_region(fw_cfg_p_base,
+					fw_cfg_p_size, "fw_cfg_mem"))
+			return -EBUSY;
+		fw_cfg_dev_base = ioremap(fw_cfg_p_base, fw_cfg_p_size);
+		if (!fw_cfg_dev_base) {
+			release_mem_region(fw_cfg_p_base, fw_cfg_p_size);
+			return -EFAULT;
+		}
+		/* set register addresses (using arm/mmio offsets) */
+		fw_cfg_reg_ctrl = fw_cfg_dev_base + 0x08;
+		fw_cfg_reg_data = fw_cfg_dev_base + 0x00;
+	} else {
+		if (!request_region(fw_cfg_p_base,
+				    fw_cfg_p_size, "fw_cfg_io"))
+			return -EBUSY;
+		fw_cfg_dev_base = ioport_map(fw_cfg_p_base, fw_cfg_p_size);
+		if (!fw_cfg_dev_base) {
+			release_region(fw_cfg_p_base, fw_cfg_p_size);
+			return -EFAULT;
+		}
+		/* set register addresses (using pc/i386/ioport offsets) */
+		fw_cfg_reg_ctrl = fw_cfg_dev_base + 0x00;
+		fw_cfg_reg_data = fw_cfg_dev_base + 0x01;
+	}
+
+	/* were custom register offsets provided (e.g. on the command line)? */
+	ctrl = platform_get_resource_byname(pdev, IORESOURCE_REG, "ctrl");
+	data = platform_get_resource_byname(pdev, IORESOURCE_REG, "data");
+	if (ctrl && data) {
+		fw_cfg_reg_ctrl = fw_cfg_dev_base + ctrl->start;
+		fw_cfg_reg_data = fw_cfg_dev_base + data->start;
+	}
+
+	/* verify fw_cfg device signature */
+	fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, 0, FW_CFG_SIG_SIZE);
+	if (memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) {
+		fw_cfg_io_cleanup();
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+/* fw_cfg revision attribute, in /sys/firmware/qemu_fw_cfg top-level dir. */
+static u32 fw_cfg_rev;
+
+static ssize_t fw_cfg_showrev(struct kobject *k, struct attribute *a, char *buf)
+{
+	return sprintf(buf, "%u\n", fw_cfg_rev);
+}
+
+static const struct {
+	struct attribute attr;
+	ssize_t (*show)(struct kobject *k, struct attribute *a, char *buf);
+} fw_cfg_rev_attr = {
+	.attr = { .name = "rev", .mode = S_IRUSR },
+	.show = fw_cfg_showrev,
+};
+
+/* fw_cfg_sysfs_entry type */
+struct fw_cfg_sysfs_entry {
+	struct kobject kobj;
+	struct fw_cfg_file f;
+	struct list_head list;
+};
+
+/* get fw_cfg_sysfs_entry from kobject member */
+static inline struct fw_cfg_sysfs_entry *to_entry(struct kobject *kobj)
+{
+	return container_of(kobj, struct fw_cfg_sysfs_entry, kobj);
+}
+
+/* fw_cfg_sysfs_attribute type */
+struct fw_cfg_sysfs_attribute {
+	struct attribute attr;
+	ssize_t (*show)(struct fw_cfg_sysfs_entry *entry, char *buf);
+};
+
+/* get fw_cfg_sysfs_attribute from attribute member */
+static inline struct fw_cfg_sysfs_attribute *to_attr(struct attribute *attr)
+{
+	return container_of(attr, struct fw_cfg_sysfs_attribute, attr);
+}
+
+/* global cache of fw_cfg_sysfs_entry objects */
+static LIST_HEAD(fw_cfg_entry_cache);
+
+/* kobjects removed lazily by kernel, mutual exclusion needed */
+static DEFINE_SPINLOCK(fw_cfg_cache_lock);
+
+static inline void fw_cfg_sysfs_cache_enlist(struct fw_cfg_sysfs_entry *entry)
+{
+	spin_lock(&fw_cfg_cache_lock);
+	list_add_tail(&entry->list, &fw_cfg_entry_cache);
+	spin_unlock(&fw_cfg_cache_lock);
+}
+
+static inline void fw_cfg_sysfs_cache_delist(struct fw_cfg_sysfs_entry *entry)
+{
+	spin_lock(&fw_cfg_cache_lock);
+	list_del(&entry->list);
+	spin_unlock(&fw_cfg_cache_lock);
+}
+
+static void fw_cfg_sysfs_cache_cleanup(void)
+{
+	struct fw_cfg_sysfs_entry *entry, *next;
+
+	list_for_each_entry_safe(entry, next, &fw_cfg_entry_cache, list) {
+		/* will end up invoking fw_cfg_sysfs_cache_delist()
+		 * via each object's release() method (i.e. destructor)
+		 */
+		kobject_put(&entry->kobj);
+	}
+}
+
+/* default_attrs: per-entry attributes and show methods */
+
+#define FW_CFG_SYSFS_ATTR(_attr) \
+struct fw_cfg_sysfs_attribute fw_cfg_sysfs_attr_##_attr = { \
+	.attr = { .name = __stringify(_attr), .mode = S_IRUSR }, \
+	.show = fw_cfg_sysfs_show_##_attr, \
+}
+
+static ssize_t fw_cfg_sysfs_show_size(struct fw_cfg_sysfs_entry *e, char *buf)
+{
+	return sprintf(buf, "%u\n", e->f.size);
+}
+
+static ssize_t fw_cfg_sysfs_show_key(struct fw_cfg_sysfs_entry *e, char *buf)
+{
+	return sprintf(buf, "%u\n", e->f.select);
+}
+
+static ssize_t fw_cfg_sysfs_show_name(struct fw_cfg_sysfs_entry *e, char *buf)
+{
+	return sprintf(buf, "%s\n", e->f.name);
+}
+
+static FW_CFG_SYSFS_ATTR(size);
+static FW_CFG_SYSFS_ATTR(key);
+static FW_CFG_SYSFS_ATTR(name);
+
+static struct attribute *fw_cfg_sysfs_entry_attrs[] = {
+	&fw_cfg_sysfs_attr_size.attr,
+	&fw_cfg_sysfs_attr_key.attr,
+	&fw_cfg_sysfs_attr_name.attr,
+	NULL,
+};
+
+/* sysfs_ops: find fw_cfg_[entry, attribute] and call appropriate show method */
+static ssize_t fw_cfg_sysfs_attr_show(struct kobject *kobj, struct attribute *a,
+				      char *buf)
+{
+	struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
+	struct fw_cfg_sysfs_attribute *attr = to_attr(a);
+
+	return attr->show(entry, buf);
+}
+
+static const struct sysfs_ops fw_cfg_sysfs_attr_ops = {
+	.show = fw_cfg_sysfs_attr_show,
+};
+
+/* release: destructor, to be called via kobject_put() */
+static void fw_cfg_sysfs_release_entry(struct kobject *kobj)
+{
+	struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
+
+	fw_cfg_sysfs_cache_delist(entry);
+	kfree(entry);
+}
+
+/* kobj_type: ties together all properties required to register an entry */
+static struct kobj_type fw_cfg_sysfs_entry_ktype = {
+	.default_attrs = fw_cfg_sysfs_entry_attrs,
+	.sysfs_ops = &fw_cfg_sysfs_attr_ops,
+	.release = fw_cfg_sysfs_release_entry,
+};
+
+/* raw-read method and attribute */
+static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj,
+				     struct bin_attribute *bin_attr,
+				     char *buf, loff_t pos, size_t count)
+{
+	struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
+
+	if (pos > entry->f.size)
+		return -EINVAL;
+
+	if (count > entry->f.size - pos)
+		count = entry->f.size - pos;
+
+	fw_cfg_read_blob(entry->f.select, buf, pos, count);
+	return count;
+}
+
+static struct bin_attribute fw_cfg_sysfs_attr_raw = {
+	.attr = { .name = "raw", .mode = S_IRUSR },
+	.read = fw_cfg_sysfs_read_raw,
+};
+
+/* kobjects representing top-level and by_key folders */
+static struct kobject *fw_cfg_top_ko;
+static struct kobject *fw_cfg_sel_ko;
+
+/* register an individual fw_cfg file */
+static int fw_cfg_register_file(const struct fw_cfg_file *f)
+{
+	int err;
+	struct fw_cfg_sysfs_entry *entry;
+
+	/* allocate new entry */
+	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
+	if (!entry)
+		return -ENOMEM;
+
+	/* set file entry information */
+	memcpy(&entry->f, f, sizeof(struct fw_cfg_file));
+
+	/* register entry under "/sys/firmware/qemu_fw_cfg/by_key/" */
+	err = kobject_init_and_add(&entry->kobj, &fw_cfg_sysfs_entry_ktype,
+				   fw_cfg_sel_ko, "%d", entry->f.select);
+	if (err)
+		goto err_register;
+
+	/* add raw binary content access */
+	err = sysfs_create_bin_file(&entry->kobj, &fw_cfg_sysfs_attr_raw);
+	if (err)
+		goto err_add_raw;
+
+	/* success, add entry to global cache */
+	fw_cfg_sysfs_cache_enlist(entry);
+	return 0;
+
+err_add_raw:
+	kobject_del(&entry->kobj);
+err_register:
+	kfree(entry);
+	return err;
+}
+
+/* iterate over all fw_cfg directory entries, registering each one */
+static int fw_cfg_register_dir_entries(void)
+{
+	int ret = 0;
+	u32 count, i;
+	struct fw_cfg_file *dir;
+	size_t dir_size;
+
+	fw_cfg_read_blob(FW_CFG_FILE_DIR, &count, 0, sizeof(count));
+	count = be32_to_cpu(count);
+	dir_size = count * sizeof(struct fw_cfg_file);
+
+	dir = kmalloc(dir_size, GFP_KERNEL);
+	if (!dir)
+		return -ENOMEM;
+
+	fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, sizeof(count), dir_size);
+
+	for (i = 0; i < count; i++) {
+		dir[i].size = be32_to_cpu(dir[i].size);
+		dir[i].select = be16_to_cpu(dir[i].select);
+		ret = fw_cfg_register_file(&dir[i]);
+		if (ret)
+			break;
+	}
+
+	kfree(dir);
+	return ret;
+}
+
+/* unregister top-level or by_key folder */
+static inline void fw_cfg_kobj_cleanup(struct kobject *kobj)
+{
+	kobject_del(kobj);
+	kobject_put(kobj);
+}
+
+static int fw_cfg_sysfs_probe(struct platform_device *pdev)
+{
+	int err;
+
+	/* NOTE: If we supported multiple fw_cfg devices, we'd first create
+	 * a subdirectory named after e.g. pdev->id, then hang per-device
+	 * by_key subdirectories underneath it. However, only
+	 * one fw_cfg device exist system-wide, so if one was already found
+	 * earlier, we might as well stop here.
+	 */
+	if (fw_cfg_sel_ko)
+		return -EBUSY;
+
+	/* create by_key subdirectory of /sys/firmware/qemu_fw_cfg/ */
+	err = -ENOMEM;
+	fw_cfg_sel_ko = kobject_create_and_add("by_key", fw_cfg_top_ko);
+	if (!fw_cfg_sel_ko)
+		goto err_sel;
+
+	/* initialize fw_cfg device i/o from platform data */
+	err = fw_cfg_do_platform_probe(pdev);
+	if (err)
+		goto err_probe;
+
+	/* get revision number, add matching top-level attribute */
+	fw_cfg_read_blob(FW_CFG_ID, &fw_cfg_rev, 0, sizeof(fw_cfg_rev));
+	fw_cfg_rev = le32_to_cpu(fw_cfg_rev);
+	err = sysfs_create_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr);
+	if (err)
+		goto err_rev;
+
+	/* process fw_cfg file directory entry, registering each file */
+	err = fw_cfg_register_dir_entries();
+	if (err)
+		goto err_dir;
+
+	/* success */
+	pr_debug("fw_cfg: loaded.\n");
+	return 0;
+
+err_dir:
+	fw_cfg_sysfs_cache_cleanup();
+	sysfs_remove_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr);
+err_rev:
+	fw_cfg_io_cleanup();
+err_probe:
+	fw_cfg_kobj_cleanup(fw_cfg_sel_ko);
+err_sel:
+	return err;
+}
+
+static int fw_cfg_sysfs_remove(struct platform_device *pdev)
+{
+	pr_debug("fw_cfg: unloading.\n");
+	fw_cfg_sysfs_cache_cleanup();
+	fw_cfg_kobj_cleanup(fw_cfg_sel_ko);
+	fw_cfg_io_cleanup();
+	return 0;
+}
+
+static const struct of_device_id fw_cfg_sysfs_mmio_match[] = {
+	{ .compatible = "qemu,fw-cfg-mmio", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, fw_cfg_sysfs_mmio_match);
+
+#ifdef CONFIG_ACPI
+static const struct acpi_device_id fw_cfg_sysfs_acpi_match[] = {
+	{ "QEMU0002", },
+	{},
+};
+MODULE_DEVICE_TABLE(acpi, fw_cfg_sysfs_acpi_match);
+#endif
+
+static struct platform_driver fw_cfg_sysfs_driver = {
+	.probe = fw_cfg_sysfs_probe,
+	.remove = fw_cfg_sysfs_remove,
+	.driver = {
+		.name = "fw_cfg",
+		.of_match_table = fw_cfg_sysfs_mmio_match,
+		.acpi_match_table = ACPI_PTR(fw_cfg_sysfs_acpi_match),
+	},
+};
+
+#ifdef CONFIG_FW_CFG_SYSFS_CMDLINE
+
+static struct platform_device *fw_cfg_cmdline_dev;
+
+static int fw_cfg_cmdline_set(const char *arg, const struct kernel_param *kp)
+{
+	struct resource res[3] = {};
+	char *str;
+	phys_addr_t base;
+	resource_size_t size, ctrl_off, data_off;
+	int processed, consumed = 0;
+
+	/* only one fw_cfg device can exist system-wide, so if one
+	 * was processed on the command line already, we might as
+	 * well stop here.
+	 */
+	if (fw_cfg_cmdline_dev) {
+		/* avoid leaking previously registered device */
+		platform_device_unregister(fw_cfg_cmdline_dev);
+		return -EINVAL;
+	}
+
+	/* consume "<size>" portion of command line argument */
+	size = memparse(arg, &str);
+
+	/* get "@<base>[:<ctrl_off>:<data_off>]" chunks */
+	processed = sscanf(str, "@%lli%n:%lli:%lli%n",
+			   &base, &consumed,
+			   &ctrl_off, &data_off, &consumed);
+
+	/* sscanf() must process precisely 1 or 3 chunks:
+	 * <base> is mandatory, optionally followed by <ctrl_off>
+	 * and <data_off>;
+	 * there must be no extra characters after the last chunk,
+	 * so str[consumed] must be '\0'.
+	 */
+	if (str[consumed] ||
+	    (processed != 1 && processed != 3))
+		return -EINVAL;
+
+	res[0].start = base;
+	res[0].end = base + size - 1;
+	res[0].flags = !strcmp(kp->name, "mmio") ? IORESOURCE_MEM :
+						   IORESOURCE_IO;
+
+	/* insert register offsets, if provided */
+	if (processed > 1) {
+		res[1].name = "ctrl";
+		res[1].start = ctrl_off;
+		res[1].flags = IORESOURCE_REG;
+		res[2].name = "data";
+		res[2].start = data_off;
+		res[2].flags = IORESOURCE_REG;
+	}
+
+	/* "processed" happens to nicely match the number of resources
+	 * we need to pass in to this platform device.
+	 */
+	fw_cfg_cmdline_dev = platform_device_register_simple("fw_cfg",
+					PLATFORM_DEVID_NONE, res, processed);
+	if (IS_ERR(fw_cfg_cmdline_dev))
+		return PTR_ERR(fw_cfg_cmdline_dev);
+
+	return 0;
+}
+
+static int fw_cfg_cmdline_get(char *buf, const struct kernel_param *kp)
+{
+	/* stay silent if device was not configured via the command
+	 * line, or if the parameter name (ioport/mmio) doesn't match
+	 * the device setting
+	 */
+	if (!fw_cfg_cmdline_dev ||
+	    (!strcmp(kp->name, "mmio") ^
+	     (fw_cfg_cmdline_dev->resource[0].flags == IORESOURCE_MEM)))
+		return 0;
+
+	switch (fw_cfg_cmdline_dev->num_resources) {
+	case 1:
+		return snprintf(buf, PAGE_SIZE, "0x%llx@0x%llx",
+				resource_size(&fw_cfg_cmdline_dev->resource[0]),
+				fw_cfg_cmdline_dev->resource[0].start);
+	case 3:
+		return snprintf(buf, PAGE_SIZE, "0x%llx@0x%llx:%llu:%llu",
+				resource_size(&fw_cfg_cmdline_dev->resource[0]),
+				fw_cfg_cmdline_dev->resource[0].start,
+				fw_cfg_cmdline_dev->resource[1].start,
+				fw_cfg_cmdline_dev->resource[2].start);
+	}
+
+	/* Should never get here */
+	WARN(1, "Unexpected number of resources: %d\n",
+		fw_cfg_cmdline_dev->num_resources);
+	return 0;
+}
+
+static const struct kernel_param_ops fw_cfg_cmdline_param_ops = {
+	.set = fw_cfg_cmdline_set,
+	.get = fw_cfg_cmdline_get,
+};
+
+device_param_cb(ioport, &fw_cfg_cmdline_param_ops, NULL, S_IRUSR);
+device_param_cb(mmio, &fw_cfg_cmdline_param_ops, NULL, S_IRUSR);
+
+#endif /* CONFIG_FW_CFG_SYSFS_CMDLINE */
+
+static int __init fw_cfg_sysfs_init(void)
+{
+	/* create /sys/firmware/qemu_fw_cfg/ top level directory */
+	fw_cfg_top_ko = kobject_create_and_add("qemu_fw_cfg", firmware_kobj);
+	if (!fw_cfg_top_ko)
+		return -ENOMEM;
+
+	return platform_driver_register(&fw_cfg_sysfs_driver);
+}
+
+static void __exit fw_cfg_sysfs_exit(void)
+{
+	platform_driver_unregister(&fw_cfg_sysfs_driver);
+
+#ifdef CONFIG_FW_CFG_SYSFS_CMDLINE
+	platform_device_unregister(fw_cfg_cmdline_dev);
+#endif
+
+	/* clean up /sys/firmware/qemu_fw_cfg/ */
+	fw_cfg_kobj_cleanup(fw_cfg_top_ko);
+}
+
+module_init(fw_cfg_sysfs_init);
+module_exit(fw_cfg_sysfs_exit);
-- 
2.4.3

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#1276654 — Re: [PATCH v5 1/4] firmware: introduce sysfs driver for QEMU's fw_cfg device

On Tue, Nov 24, 2015 at 04:14:50AM +0800, kbuild test robot wrote:
> Hi Gabriel,
> 
> [auto build test WARNING on v4.4-rc2]
> [also build test WARNING on next-20151123]
> [cannot apply to robh/for-next]
> 
> url:    https://github.com/0day-ci/linux/commits/Gabriel-L-Somlo/SysFS-driver-for-QEMU-fw_cfg-device/20151124-000402
> config: arm-allyesconfig (attached as .config)
> reproduce:
>         wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # save the attached .config to linux build tree
>         make.cross ARCH=arm 
> 
> All warnings (new ones prefixed by >>):
> 
>    drivers/firmware/qemu_fw_cfg.c: In function 'fw_cfg_cmdline_set':
> >> drivers/firmware/qemu_fw_cfg.c:510:7: warning: format '%lli' expects argument of type 'long long int *', but argument 3 has type 'phys_addr_t *' [-Wformat=]
>           &ctrl_off, &data_off, &consumed);
>           ^

Oh, I think I know why this happened:

...
        phys_addr_t base;
        resource_size_t size, ctrl_off, data_off;
...
        /* get "@<base>[:<ctrl_off>:<data_off>]" chunks */
        processed = sscanf(str, "@%lli%n:%lli:%lli%n"
                           &base, &consumed,
                           &ctrl_off, &data_off, &consumed);
...

On some architectures, phys_addr_t (and resource_size_t) are u32,
rather than u64. In include/linux/types.h we have:

...
#ifdef CONFIG_PHYS_ADDR_T_64BIT
typedef u64 phys_addr_t;
#else
typedef u32 phys_addr_t;
#endif
...

So, I could use u64 instead of phys_addr_t and resource_size_t, and
keep "%lli" (or "%Li"), but then I'd have to check if the parsed value
would overflow a 32-bit address value on arches where phys_addr_t is
u32, which would make things a bit more messy and awkward.

I'm planning on #ifdef-ing the format string instead:

#ifdef CONFIG_PHYS_ADDR_T_64BIT
#define PH_ADDR_SCAN_FMT "@%Li%n:%Li:%Li%n"
#else
#define PH_ADDR_SCAN_FMT "@%li%n:%li:%li%n"
#endif
...
        processed = sscanf(str, PH_ADDR_SCAN_FMT,
                           &base, &consumed,
                           &ctrl_off, &data_off, &consumed);


This should make the warning go away, and be correct. Does that sound
like a valid plan, or is there some other stylistic reason I should
stay away from doing it that way ?

thanks,
--Gabriel

> >> drivers/firmware/qemu_fw_cfg.c:510:7: warning: format '%lli' expects argument of type 'long long int *', but argument 5 has type 'resource_size_t *' [-Wformat=]
>    drivers/firmware/qemu_fw_cfg.c:510:7: warning: format '%lli' expects argument of type 'long long int *', but argument 6 has type 'resource_size_t *' [-Wformat=]
>    drivers/firmware/qemu_fw_cfg.c: In function 'fw_cfg_cmdline_get':
> >> drivers/firmware/qemu_fw_cfg.c:563:5: warning: format '%llx' expects argument of type 'long long unsigned int', but argument 4 has type 'resource_size_t' [-Wformat=]
>         fw_cfg_cmdline_dev->resource[0].start);
>         ^
>    drivers/firmware/qemu_fw_cfg.c:563:5: warning: format '%llx' expects argument of type 'long long unsigned int', but argument 5 has type 'resource_size_t' [-Wformat=]
>    drivers/firmware/qemu_fw_cfg.c:569:5: warning: format '%llx' expects argument of type 'long long unsigned int', but argument 4 has type 'resource_size_t' [-Wformat=]
>         fw_cfg_cmdline_dev->resource[2].start);
>         ^
>    drivers/firmware/qemu_fw_cfg.c:569:5: warning: format '%llx' expects argument of type 'long long unsigned int', but argument 5 has type 'resource_size_t' [-Wformat=]
> >> drivers/firmware/qemu_fw_cfg.c:569:5: warning: format '%llu' expects argument of type 'long long unsigned int', but argument 6 has type 'resource_size_t' [-Wformat=]
>    drivers/firmware/qemu_fw_cfg.c:569:5: warning: format '%llu' expects argument of type 'long long unsigned int', but argument 7 has type 'resource_size_t' [-Wformat=]
> 
> vim +510 drivers/firmware/qemu_fw_cfg.c
> 
>    504		/* consume "<size>" portion of command line argument */
>    505		size = memparse(arg, &str);
>    506	
>    507		/* get "@<base>[:<ctrl_off>:<data_off>]" chunks */
>    508		processed = sscanf(str, "@%lli%n:%lli:%lli%n",
>    509				   &base, &consumed,
>  > 510				   &ctrl_off, &data_off, &consumed);
>    511	
>    512		/* sscanf() must process precisely 1 or 3 chunks:
>    513		 * <base> is mandatory, optionally followed by <ctrl_off>
>    514		 * and <data_off>;
>    515		 * there must be no extra characters after the last chunk,
>    516		 * so str[consumed] must be '\0'.
>    517		 */
>    518		if (str[consumed] ||
>    519		    (processed != 1 && processed != 3))
>    520			return -EINVAL;
>    521	
>    522		res[0].start = base;
>    523		res[0].end = base + size - 1;
>    524		res[0].flags = !strcmp(kp->name, "mmio") ? IORESOURCE_MEM :
>    525							   IORESOURCE_IO;
>    526	
>    527		/* insert register offsets, if provided */
>    528		if (processed > 1) {
>    529			res[1].name = "ctrl";
>    530			res[1].start = ctrl_off;
>    531			res[1].flags = IORESOURCE_REG;
>    532			res[2].name = "data";
>    533			res[2].start = data_off;
>    534			res[2].flags = IORESOURCE_REG;
>    535		}
>    536	
>    537		/* "processed" happens to nicely match the number of resources
>    538		 * we need to pass in to this platform device.
>    539		 */
>    540		fw_cfg_cmdline_dev = platform_device_register_simple("fw_cfg",
>    541						PLATFORM_DEVID_NONE, res, processed);
>    542		if (IS_ERR(fw_cfg_cmdline_dev))
>    543			return PTR_ERR(fw_cfg_cmdline_dev);
>    544	
>    545		return 0;
>    546	}
>    547	
>    548	static int fw_cfg_cmdline_get(char *buf, const struct kernel_param *kp)
>    549	{
>    550		/* stay silent if device was not configured via the command
>    551		 * line, or if the parameter name (ioport/mmio) doesn't match
>    552		 * the device setting
>    553		 */
>    554		if (!fw_cfg_cmdline_dev ||
>    555		    (!strcmp(kp->name, "mmio") ^
>    556		     (fw_cfg_cmdline_dev->resource[0].flags == IORESOURCE_MEM)))
>    557			return 0;
>    558	
>    559		switch (fw_cfg_cmdline_dev->num_resources) {
>    560		case 1:
>    561			return snprintf(buf, PAGE_SIZE, "0x%llx@0x%llx",
>    562					resource_size(&fw_cfg_cmdline_dev->resource[0]),
>  > 563					fw_cfg_cmdline_dev->resource[0].start);
>    564		case 3:
>    565			return snprintf(buf, PAGE_SIZE, "0x%llx@0x%llx:%llu:%llu",
>    566					resource_size(&fw_cfg_cmdline_dev->resource[0]),
>    567					fw_cfg_cmdline_dev->resource[0].start,
>    568					fw_cfg_cmdline_dev->resource[1].start,
>  > 569					fw_cfg_cmdline_dev->resource[2].start);
>    570		}
>    571	
>    572		/* Should never get here */
> 
> ---
> 0-DAY kernel test infrastructure                Open Source Technology Center
> https://lists.01.org/pipermail/kbuild-all                   Intel Corporation


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#1276675 — Re: [Qemu-devel] [PATCH v5 1/4] firmware: introduce sysfs driver for QEMU's fw_cfg device

[Multipart message — attachments visible in raw view] — view raw

On 11/24/2015 09:55 AM, Gabriel L. Somlo wrote:
> On Tue, Nov 24, 2015 at 04:14:50AM +0800, kbuild test robot wrote:

>>
>>    drivers/firmware/qemu_fw_cfg.c: In function 'fw_cfg_cmdline_set':
>>>> drivers/firmware/qemu_fw_cfg.c:510:7: warning: format '%lli' expects argument of type 'long long int *', but argument 3 has type 'phys_addr_t *' [-Wformat=]
>>           &ctrl_off, &data_off, &consumed);
>>           ^
> 
> Oh, I think I know why this happened:
> 

> 
> So, I could use u64 instead of phys_addr_t and resource_size_t, and
> keep "%lli" (or "%Li"), but then I'd have to check if the parsed value

%Li is not POSIX.  Don't use it (stick with %lli).

> would overflow a 32-bit address value on arches where phys_addr_t is
> u32, which would make things a bit more messy and awkward.
> 
> I'm planning on #ifdef-ing the format string instead:
> 
> #ifdef CONFIG_PHYS_ADDR_T_64BIT
> #define PH_ADDR_SCAN_FMT "@%Li%n:%Li:%Li%n"
> #else
> #define PH_ADDR_SCAN_FMT "@%li%n:%li:%li%n"
> #endif

A more typical approach is akin to <inttypes.h>; have PH_ADDR_FMT
defined to either "lli" or "li", then write sscanf(str, "@%"PH_ADDR_FMT
"%n:..., ...), using PH_ADDR_FMT multiple times.

> ...
>         processed = sscanf(str, PH_ADDR_SCAN_FMT,
>                            &base, &consumed,
>                            &ctrl_off, &data_off, &consumed);

Umm, why are you passing &consumed to more than one sscanf() %?  That's
(probably) undefined behavior.

[In general, sscanf() is a horrid interface to use for parsing integers
- it has undefined behavior if the input text would trigger integer
overflow, making it safe to use ONLY on text that you control and can
guarantee won't overflow. By the time you've figured out if untrusted
text meets the requirement for safe parsing via sscanf(), you've
practically already parsed it via safer strtol() and friends.]

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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#1276683 — Re: [Qemu-devel] [PATCH v5 1/4] firmware: introduce sysfs driver for QEMU's fw_cfg device

On 11/24/15 18:38, Eric Blake wrote:
> On 11/24/2015 09:55 AM, Gabriel L. Somlo wrote:
>> On Tue, Nov 24, 2015 at 04:14:50AM +0800, kbuild test robot wrote:
> 
>>>
>>>    drivers/firmware/qemu_fw_cfg.c: In function 'fw_cfg_cmdline_set':
>>>>> drivers/firmware/qemu_fw_cfg.c:510:7: warning: format '%lli' expects argument of type 'long long int *', but argument 3 has type 'phys_addr_t *' [-Wformat=]
>>>           &ctrl_off, &data_off, &consumed);
>>>           ^
>>
>> Oh, I think I know why this happened:
>>
> 
>>
>> So, I could use u64 instead of phys_addr_t and resource_size_t, and
>> keep "%lli" (or "%Li"), but then I'd have to check if the parsed value
> 
> %Li is not POSIX.  Don't use it (stick with %lli).
> 
>> would overflow a 32-bit address value on arches where phys_addr_t is
>> u32, which would make things a bit more messy and awkward.
>>
>> I'm planning on #ifdef-ing the format string instead:
>>
>> #ifdef CONFIG_PHYS_ADDR_T_64BIT
>> #define PH_ADDR_SCAN_FMT "@%Li%n:%Li:%Li%n"
>> #else
>> #define PH_ADDR_SCAN_FMT "@%li%n:%li:%li%n"
>> #endif
> 
> A more typical approach is akin to <inttypes.h>; have PH_ADDR_FMT
> defined to either "lli" or "li", then write sscanf(str, "@%"PH_ADDR_FMT
> "%n:..., ...), using PH_ADDR_FMT multiple times.
> 
>> ...
>>         processed = sscanf(str, PH_ADDR_SCAN_FMT,
>>                            &base, &consumed,
>>                            &ctrl_off, &data_off, &consumed);
> 
> Umm, why are you passing &consumed to more than one sscanf() %?  That's
> (probably) undefined behavior.
> 
> [In general, sscanf() is a horrid interface to use for parsing integers
> - it has undefined behavior if the input text would trigger integer
> overflow, making it safe to use ONLY on text that you control and can
> guarantee won't overflow. By the time you've figured out if untrusted
> text meets the requirement for safe parsing via sscanf(), you've
> practically already parsed it via safer strtol() and friends.]
> 

Yes, but this is the kernel, which may or may not follow POSIX
semantics. (And may or may not curse at POSIX in the process, either
way! :))

Laszlo
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#1276701 — Re: [Qemu-devel] [PATCH v5 1/4] firmware: introduce sysfs driver for QEMU's fw_cfg device

On Tue, Nov 24, 2015 at 10:38:18AM -0700, Eric Blake wrote:
> On 11/24/2015 09:55 AM, Gabriel L. Somlo wrote:
> > On Tue, Nov 24, 2015 at 04:14:50AM +0800, kbuild test robot wrote:
> 
> >>
> >>    drivers/firmware/qemu_fw_cfg.c: In function 'fw_cfg_cmdline_set':
> >>>> drivers/firmware/qemu_fw_cfg.c:510:7: warning: format '%lli' expects argument of type 'long long int *', but argument 3 has type 'phys_addr_t *' [-Wformat=]
> >>           &ctrl_off, &data_off, &consumed);
> >>           ^
> > 
> > Oh, I think I know why this happened:
> > 
> 
> > 
> > So, I could use u64 instead of phys_addr_t and resource_size_t, and
> > keep "%lli" (or "%Li"), but then I'd have to check if the parsed value
> 
> %Li is not POSIX.  Don't use it (stick with %lli).
> 
> > would overflow a 32-bit address value on arches where phys_addr_t is
> > u32, which would make things a bit more messy and awkward.
> > 
> > I'm planning on #ifdef-ing the format string instead:
> > 
> > #ifdef CONFIG_PHYS_ADDR_T_64BIT
> > #define PH_ADDR_SCAN_FMT "@%Li%n:%Li:%Li%n"
> > #else
> > #define PH_ADDR_SCAN_FMT "@%li%n:%li:%li%n"
> > #endif
> 
> A more typical approach is akin to <inttypes.h>; have PH_ADDR_FMT
> defined to either "lli" or "li", then write sscanf(str, "@%"PH_ADDR_FMT
> "%n:..., ...), using PH_ADDR_FMT multiple times.

That sounds almost like it should be a separate patch against
include/linux/types.h:

diff --git a/include/linux/types.h b/include/linux/types.h
index 70d8500..35be16e 100644
--- a/include/linux/types.h
+++ b/include/linux/types.h
@@ -160,8 +160,10 @@ typedef unsigned __bitwise__ oom_flags_t;
 
 #ifdef CONFIG_PHYS_ADDR_T_64BIT
 typedef u64 phys_addr_t;
+#define __PHYS_ADDR_PREFIX "ll"
 #else
 typedef u32 phys_addr_t;
+#define __PHYS_ADDR_PREFIX "l"
 #endif
 
 typedef phys_addr_t resource_size_t;

But whether it's a good idea for me to detour from fw_cfg/sysfs into
sorting this out with the kernel community right now, I don't know :)

I'll just try to do it inside the fw_cfg sysfs driver for now, see how
that goes...

> 
> > ...
> >         processed = sscanf(str, PH_ADDR_SCAN_FMT,
> >                            &base, &consumed,
> >                            &ctrl_off, &data_off, &consumed);
> 
> Umm, why are you passing &consumed to more than one sscanf() %?  That's
> (probably) undefined behavior.

Input might end after reading 'base', in which case %n would store the
next character's index in consumed, and evaluate (but otherwise
ignore) the remaining pointer arguments (including the second &consumed).

Or, it might end after reading data_off, then the earlier value of
consumed gets overwritten with the new (past data_off) index. I get to
verify that str[index] is '\0', i.e. that there were no left-over,
unprocessed characters, whether I got one or three items processed by
scanf.

I don't think passing '&consumed' in twice is a problem. I also didn't
cleverly come up with this myself, but rather lifted it from
drivers/virtio/virtio_mmio.c, so at least there's precedent :)

> [In general, sscanf() is a horrid interface to use for parsing integers
> - it has undefined behavior if the input text would trigger integer
> overflow, making it safe to use ONLY on text that you control and can
> guarantee won't overflow. By the time you've figured out if untrusted
> text meets the requirement for safe parsing via sscanf(), you've
> practically already parsed it via safer strtol() and friends.]

Just like (I think) is the case with virtio_mmio, this is an optional
feature to allow specifying a base address, range, and register
offsets for fw_cfg via the insmod (or modprobe) command line, so one
would already have to be root. Also, perfectly well-formated base and
size values could be used to hose the system, which is why virtio_mmio
(and also fw_cfg) leave this feature off by default, and recommend
caution before one would turn it on.

Thanks much,
--Gabriel
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