efivars: Add compatibility code for compat tasks

It seems people are using 32-bit efibootmgr on top of 64-bit kernels,
which will currently fail horribly when using the efivars interface,
which is the traditional efibootmgr backend (the other being efivarfs).

Since there is no versioning info in the data structure, figure out when
we need to munge the structure data via judicious use of
is_compat_task().

Cc: Mike Waychison <[e-mail]>
Signed-off-by: Matt Fleming <[e-mail]>

drivers/firmware/efi/efivars.c

···
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/ucs2_string.h>
+#include <linux/compat.h>
 
 #define EFIVARS_VERSION "0.08"
 #define EFIVARS_DATE "2004-May-17"
···
 
 static struct bin_attribute *efivars_new_var;
 static struct bin_attribute *efivars_del_var;
+
+struct compat_efi_variable {
+	efi_char16_t  VariableName[EFI_VAR_NAME_LEN/sizeof(efi_char16_t)];
+	efi_guid_t    VendorGuid;
+	__u32         DataSize;
+	__u8          Data[1024];
+	__u32         Status;
+	__u32         Attributes;
+} __packed;
 
 struct efivar_attribute {
 	struct attribute attr;
···
 	return 0;
 }
 
+static inline bool is_compat(void)
+{
+	if (IS_ENABLED(CONFIG_COMPAT) && is_compat_task())
+		return true;
+
+	return false;
+}
+
+static void
+copy_out_compat(struct efi_variable *dst, struct compat_efi_variable *src)
+{
+	memcpy(dst->VariableName, src->VariableName, EFI_VAR_NAME_LEN);
+	memcpy(dst->Data, src->Data, sizeof(src->Data));
+
+	dst->VendorGuid = src->VendorGuid;
+	dst->DataSize = src->DataSize;
+	dst->Attributes = src->Attributes;
+}
+
 /*
  * We allow each variable to be edited via rewriting the
  * entire efi variable structure.
···
 	u8 *data;
 	int err;
 
-	if (count != sizeof(struct efi_variable))
-		return -EINVAL;
+	if (is_compat()) {
+		struct compat_efi_variable *compat;
 
-	new_var = (struct efi_variable *)buf;
+		if (count != sizeof(*compat))
+			return -EINVAL;
 
-	attributes = new_var->Attributes;
-	vendor = new_var->VendorGuid;
-	name = new_var->VariableName;
-	size = new_var->DataSize;
-	data = new_var->Data;
+		compat = (struct compat_efi_variable *)buf;
+		attributes = compat->Attributes;
+		vendor = compat->VendorGuid;
+		name = compat->VariableName;
+		size = compat->DataSize;
+		data = compat->Data;
 
-	err = sanity_check(var, name, vendor, size, attributes, data);
-	if (err)
-		return err;
+		err = sanity_check(var, name, vendor, size, attributes, data);
+		if (err)
+			return err;
 
-	memcpy(&entry->var, new_var, count);
+		copy_out_compat(&entry->var, compat);
+	} else {
+		if (count != sizeof(struct efi_variable))
+			return -EINVAL;
+
+		new_var = (struct efi_variable *)buf;
+
+		attributes = new_var->Attributes;
+		vendor = new_var->VendorGuid;
+		name = new_var->VariableName;
+		size = new_var->DataSize;
+		data = new_var->Data;
+
+		err = sanity_check(var, name, vendor, size, attributes, data);
+		if (err)
+			return err;
+
+		memcpy(&entry->var, new_var, count);
+	}
 
 	err = efivar_entry_set(entry, attributes, size, data, NULL);
 	if (err) {
···
 efivar_show_raw(struct efivar_entry *entry, char *buf)
 {
 	struct efi_variable *var = &entry->var;
+	struct compat_efi_variable *compat;
+	size_t size;
 
 	if (!entry || !buf)
 		return 0;
···
 			     &entry->var.DataSize, entry->var.Data))
 		return -EIO;
 
-	memcpy(buf, var, sizeof(*var));
+	if (is_compat()) {
+		compat = (struct compat_efi_variable *)buf;
 
-	return sizeof(*var);
+		size = sizeof(*compat);
+		memcpy(compat->VariableName, var->VariableName,
+			EFI_VAR_NAME_LEN);
+		memcpy(compat->Data, var->Data, sizeof(compat->Data));
+
+		compat->VendorGuid = var->VendorGuid;
+		compat->DataSize = var->DataSize;
+		compat->Attributes = var->Attributes;
+	} else {
+		size = sizeof(*var);
+		memcpy(buf, var, size);
+	}
+
+	return size;
 }
 
 /*
···
 			     struct bin_attribute *bin_attr,
 			     char *buf, loff_t pos, size_t count)
 {
+	struct compat_efi_variable *compat = (struct compat_efi_variable *)buf;
 	struct efi_variable *new_var = (struct efi_variable *)buf;
 	struct efivar_entry *new_entry;
+	bool need_compat = is_compat();
 	efi_char16_t *name;
 	unsigned long size;
 	u32 attributes;
···
 	if (!capable(CAP_SYS_ADMIN))
 		return -EACCES;
 
-	if (count != sizeof(*new_var))
-		return -EINVAL;
+	if (need_compat) {
+		if (count != sizeof(*compat))
+			return -EINVAL;
 
-	attributes = new_var->Attributes;
-	name = new_var->VariableName;
-	size = new_var->DataSize;
-	data = new_var->Data;
+		attributes = compat->Attributes;
+		name = compat->VariableName;
+		size = compat->DataSize;
+		data = compat->Data;
+	} else {
+		if (count != sizeof(*new_var))
+			return -EINVAL;
+
+		attributes = new_var->Attributes;
+		name = new_var->VariableName;
+		size = new_var->DataSize;
+		data = new_var->Data;
+	}
 
 	if ((attributes & ~EFI_VARIABLE_MASK) != 0 ||
 	    efivar_validate(name, data, size) == false) {
···
 	if (!new_entry)
 		return -ENOMEM;
 
-	memcpy(&new_entry->var, new_var, sizeof(*new_var));
+	if (need_compat)
+		copy_out_compat(&new_entry->var, compat);
+	else
+		memcpy(&new_entry->var, new_var, sizeof(*new_var));
 
 	err = efivar_entry_set(new_entry, attributes, size,
 			       data, &efivar_sysfs_list);
···
 			     char *buf, loff_t pos, size_t count)
 {
 	struct efi_variable *del_var = (struct efi_variable *)buf;
+	struct compat_efi_variable *compat;
 	struct efivar_entry *entry;
 	efi_char16_t *name;
 	efi_guid_t vendor;
···
 	if (!capable(CAP_SYS_ADMIN))
 		return -EACCES;
 
-	if (count != sizeof(*del_var))
-		return -EINVAL;
+	if (is_compat()) {
+		if (count != sizeof(*compat))
+			return -EINVAL;
 
-	name = del_var->VariableName;
-	vendor = del_var->VendorGuid;
+		compat = (struct compat_efi_variable *)buf;
+		name = compat->VariableName;
+		vendor = compat->VendorGuid;
+	} else {
+		if (count != sizeof(*del_var))
+			return -EINVAL;
+
+		name = del_var->VariableName;
+		vendor = del_var->VendorGuid;
+	}
 
 	efivar_entry_iter_begin();
 	entry = efivar_entry_find(name, vendor, &efivar_sysfs_list, true);