[PATCH] firmware: dmi-sysfs: add SMBIOS entry point area attribute

[Ivan Khoronzhuk]

Some utils, like dmidecode and smbios, needs to access SMBIOS entry
table area in order to get information like SMBIOS version, size, etc.
Currently it's done via /dev/mem. But for situation when /dev/mem
usage is disabled, the utils have to use dmi sysfs instead, which
doesn't represent SMBIOS entry. So this patch adds SMBIOS area to
dmi-sysfs in order to allow utils in question to work correctly with
dmi sysfs interface.

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx>
---
 Documentation/ABI/testing/sysfs-firmware-dmi | 10 +++++++
 drivers/firmware/dmi-sysfs.c                 | 42 ++++++++++++++++++++++++++++
 drivers/firmware/dmi_scan.c                  | 26 +++++++++++++++++
 include/linux/dmi.h                          |  3 ++
 4 files changed, 81 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-firmware-dmi b/Documentation/ABI/testing/sysfs-firmware-dmi
index c78f9ab..3a9ffe8 100644
--- a/Documentation/ABI/testing/sysfs-firmware-dmi
+++ b/Documentation/ABI/testing/sysfs-firmware-dmi
@@ -12,6 +12,16 @@ Description:
 		cannot ensure that the data as exported to userland is
 		without error either.
 
+		The firmware provides DMI structures as a packed list of
+		data referenced by a SMBIOS table entry point. The SMBIOS
+		entry point contains general information, like SMBIOS
+		version, DMI table size, etc. The structure, content and
+		size of SMBIOS entry point is dependent on SMBIOS version.
+		That's why SMBIOS entry point is represented in dmi sysfs
+		like a raw attribute and is accessible via
+		/sys/firmware/dmi/smbios_raw_header. The format of SMBIOS
+		entry point header can be read in SMBIOS specification.
+
 		DMI is structured as a large table of entries, where
 		each entry has a common header indicating the type and
 		length of the entry, as well as a firmware-provided
diff --git a/drivers/firmware/dmi-sysfs.c b/drivers/firmware/dmi-sysfs.c
index e0f1cb3..9b396d7 100644
--- a/drivers/firmware/dmi-sysfs.c
+++ b/drivers/firmware/dmi-sysfs.c
@@ -29,6 +29,8 @@
 #define MAX_ENTRY_TYPE 255 /* Most of these aren't used, but we consider
 			      the top entry type is only 8 bits */
 
+static const u8 *smbios_raw_header;
+
 struct dmi_sysfs_entry {
 	struct dmi_header dh;
 	struct kobject kobj;
@@ -646,9 +648,37 @@ static void cleanup_entry_list(void)
 	}
 }
 
+static ssize_t smbios_entry_area_raw_read(struct file *filp,
+					  struct kobject *kobj,
+					  struct bin_attribute *bin_attr,
+					  char *buf, loff_t pos, size_t count)
+{
+	ssize_t size;
+
+	size = bin_attr->size;
+
+	if (size > pos)
+		size -= pos;
+	else
+		return 0;
+
+	if (count < size)
+		size = count;
+
+	memcpy(buf, &smbios_raw_header[pos], size);
+
+	return size;
+}
+
+static struct bin_attribute smbios_raw_area_attr = {
+	.read = smbios_entry_area_raw_read,
+	.attr = {.name = "smbios_raw_header", .mode = 0400},
+};
+
 static int __init dmi_sysfs_init(void)
 {
 	int error = -ENOMEM;
+	int size;
 	int val;
 
 	/* Set up our directory */
@@ -669,6 +699,18 @@ static int __init dmi_sysfs_init(void)
 		goto err;
 	}
 
+	smbios_raw_header = dmi_get_smbios_entry_area(&size);
+	if (!smbios_raw_header) {
+		pr_debug("dmi-sysfs: SMBIOS raw data is not available.\n");
+		error = -EINVAL;
+		goto err;
+	}
+
+	/* Create the raw binary file to access the entry area */
+	smbios_raw_area_attr.size = size;
+	if (sysfs_create_bin_file(dmi_kobj, &smbios_raw_area_attr))
+		goto err;
+
 	pr_debug("dmi-sysfs: loaded.\n");
 
 	return 0;
diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
index c5f7b4e..d55c712 100644
--- a/drivers/firmware/dmi_scan.c
+++ b/drivers/firmware/dmi_scan.c
@@ -113,6 +113,8 @@ static void dmi_table(u8 *buf, int len, int num,
 	}
 }
 
+static u8 smbios_header[32];
+static int smbios_header_size;
 static phys_addr_t dmi_base;
 static u16 dmi_len;
 static u16 dmi_num;
@@ -474,6 +476,8 @@ static int __init dmi_present(const u8 *buf)
 	if (memcmp(buf, "_SM_", 4) == 0 &&
 	    buf[5] < 32 && dmi_checksum(buf, buf[5])) {
 		smbios_ver = get_unaligned_be16(buf + 6);
+		smbios_header_size = buf[5];
+		memcpy(smbios_header, buf, smbios_header_size);
 
 		/* Some BIOS report weird SMBIOS version, fix that up */
 		switch (smbios_ver) {
@@ -505,6 +509,8 @@ static int __init dmi_present(const u8 *buf)
 				pr_info("SMBIOS %d.%d present.\n",
 				       dmi_ver >> 8, dmi_ver & 0xFF);
 			} else {
+				smbios_header_size = 15;
+				memcpy(smbios_header, buf, smbios_header_size);
 				dmi_ver = (buf[14] & 0xF0) << 4 |
 					   (buf[14] & 0x0F);
 				pr_info("Legacy DMI %d.%d present.\n",
@@ -530,6 +536,8 @@ static int __init dmi_smbios3_present(const u8 *buf)
 		dmi_ver = get_unaligned_be16(buf + 7);
 		dmi_len = get_unaligned_le32(buf + 12);
 		dmi_base = get_unaligned_le64(buf + 16);
+		smbios_header_size = buf[6];
+		memcpy(smbios_header, buf, smbios_header_size);
 
 		/*
 		 * The 64-bit SMBIOS 3.0 entry point no longer has a field
@@ -941,3 +949,21 @@ void dmi_memdev_name(u16 handle, const char **bank, const char **device)
 	}
 }
 EXPORT_SYMBOL_GPL(dmi_memdev_name);
+
+/**
+ * dmi_get_smbios_entry_area - copy SMBIOS entry point area to array.
+ * @size - pointer to assign actual size of SMBIOS entry point area.
+ *
+ * returns NULL if table is not available, otherwise returns pointer on
+ * SMBIOS entry point area array.
+ */
+const u8 *dmi_get_smbios_entry_area(int *size)
+{
+	if (!smbios_header_size || !dmi_available)
+		return NULL;
+
+	*size = smbios_header_size;
+
+	return smbios_header;
+}
+EXPORT_SYMBOL_GPL(dmi_get_smbios_entry_area);
diff --git a/include/linux/dmi.h b/include/linux/dmi.h
index f820f0a..8e1a28d 100644
--- a/include/linux/dmi.h
+++ b/include/linux/dmi.h
@@ -109,6 +109,7 @@ extern int dmi_walk(void (*decode)(const struct dmi_header *, void *),
 	void *private_data);
 extern bool dmi_match(enum dmi_field f, const char *str);
 extern void dmi_memdev_name(u16 handle, const char **bank, const char **device);
+const u8 *dmi_get_smbios_entry_area(int *size);
 
 #else
 
@@ -140,6 +141,8 @@ static inline void dmi_memdev_name(u16 handle, const char **bank,
 		const char **device) { }
 static inline const struct dmi_system_id *
 	dmi_first_match(const struct dmi_system_id *list) { return NULL; }
+static inline const u8 *dmi_get_smbios_entry_area(int *size)
+	{ return NULL; }
 
 #endif
 
-- 
1.9.1


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