[PATCH v6 2/5] efi: Add embedded peripheral firmware support

Hans de Goede
2018-06-01T12:53:27Z

Just like with PCI options ROMs, which we save in the setup_efi_pci*
functions from arch/x86/boot/compressed/eboot.c, the EFI code / ROM itself
sometimes may contain data which is useful/necessary for peripheral drivers
to have access to.

Specifically the EFI code may contain an embedded copy of firmware which
needs to be (re)loaded into the peripheral. Normally such firmware would be
part of linux-firmware, but in some cases this is not feasible, for 2
reasons:

1) The firmware is customized for a specific use-case of the chipset / use
with a specific hardware model, so we cannot have a single firmware file
for the chipset. E.g. touchscreen controller firmwares are compiled
specifically for the hardware model they are used with, as they are
calibrated for a specific model digitizer.

2) Despite repeated attempts we have failed to get permission to
redistribute the firmware. This is especially a problem with customized
firmwares, these get created by the chip vendor for a specific ODM and the
copyright may partially belong with the ODM, so the chip vendor cannot
give a blanket permission to distribute these.

This commit adds support for finding peripheral firmware embedded in the
EFI code and making this available to peripheral drivers through the
standard firmware loading mechanism.

Note we check the EFI_BOOT_SERVICES_CODE for embedded firmware near the end
of start_kernel(), just before calling rest_init(), this is on purpose
because the typical EFI_BOOT_SERVICES_CODE memory-segment is too large for
early_memremap(), so the check must be done after mm_init(). This relies
on EFI_BOOT_SERVICES_CODE not being free-ed until efi_free_boot_services()
is called, which means that this will only work on x86 for now.

Reported-by: Dave Olsthoorn <dave@bewaar.me>
Suggested-by: Peter Jones <pjones@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
Changes in v6:
-Rework code to remove casts from if (prefix == mem) comparison
-Use SHA256 hashes instead of crc32 sums
-Add new READING_FIRMWARE_EFI_EMBEDDED read_file_id and use it
-Call security_kernel_read_file(NULL, READING_FIRMWARE_EFI_EMBEDDED)
to check if this is allowed before looking at EFI embedded fw
-Document why we are not using the PI Firmware Volume protocol

Changes in v5:
-Rename the EFI_BOOT_SERVICES flag to EFI_PRESERVE_BS_REGIONS

Changes in v4:
-Drop note in docs about EFI_FIRMWARE_VOLUME_PROTOCOL, it is not part of
UEFI proper, so the EFI maintainers don't want us referring people to it
-Use new EFI_BOOT_SERVICES flag
-Put the new fw_get_efi_embedded_fw() function in its own fallback_efi.c
file which only gets built when EFI_EMBEDDED_FIRMWARE is selected
-Define an empty stub for fw_get_efi_embedded_fw() in fallback.h hwen
EFI_EMBEDDED_FIRMWARE is not selected, to avoid the need for #ifdefs
in firmware_loader/main.c
-Properly call security_kernel_post_read_file() on the firmware returned
by efi_get_embedded_fw() to make sure that we are allowed to use it

Changes in v3:
-Fix the docs using "efi-embedded-fw" as property name instead of
"efi-embedded-firmware"

Changes in v2:
-Rebased on driver-core/driver-core-next
-Add documentation describing the EFI embedded firmware mechanism to:
Documentation/driver-api/firmware/request_firmware.rst
-Add a new EFI_EMBEDDED_FIRMWARE Kconfig bool and only build the embedded
fw support if this is set. This is an invisible option which should be
selected by drivers which need this
-Remove the efi_embedded_fw_desc and dmi_system_id-s for known devices
from the efi-embedded-fw code, instead drivers using this are expected to
export a dmi_system_id array, with each entries' driver_data pointing to a
efi_embedded_fw_desc struct and register this with the efi-embedded-fw code
-Use kmemdup to make a copy instead of efi_mem_reserve()-ing the firmware,
this avoids us messing with the EFI memmap and avoids the need to make
changes to efi_mem_desc_lookup()
-Make the firmware-loader code only fallback to efi_get_embedded_fw() if the
passed in device has the "efi-embedded-firmware" device-property bool set
-Skip usermodehelper fallback when "efi-embedded-firmware" device-property
is set
---
.../driver-api/firmware/request_firmware.rst | 76 +++++++++
drivers/base/firmware_loader/Makefile | 1 +
drivers/base/firmware_loader/fallback.h | 12 ++
drivers/base/firmware_loader/fallback_efi.c | 56 +++++++
drivers/base/firmware_loader/main.c | 2 +
drivers/firmware/efi/Kconfig | 3 +
drivers/firmware/efi/Makefile | 1 +
drivers/firmware/efi/embedded-firmware.c | 148 ++++++++++++++++++
include/linux/efi.h | 6 +
include/linux/efi_embedded_fw.h | 25 +++
include/linux/fs.h | 1 +
init/main.c | 3 +
12 files changed, 334 insertions(+)
create mode 100644 drivers/base/firmware_loader/fallback_efi.c
create mode 100644 drivers/firmware/efi/embedded-firmware.c
create mode 100644 include/linux/efi_embedded_fw.h

diff --git a/Documentation/driver-api/firmware/request_firmware.rst b/Documentation/driver-api/firmware/request_firmware.rst
index f62bdcbfed5b..66ab91f3357d 100644
--- a/Documentation/driver-api/firmware/request_firmware.rst
+++ b/Documentation/driver-api/firmware/request_firmware.rst
@@ -73,3 +73,79 @@ If something went wrong request_firmware() returns non-zero and fw_entry
is set to NULL. Once your driver is done with processing the firmware it
can call call release_firmware(fw_entry) to release the firmware image
and any related resource.
+
+EFI embedded firmware support
+=============================
+
+On some devices the system's EFI code / ROM may contain an embedded copy
+of firmware for some of the system's integrated peripheral devices and
+the peripheral's Linux device-driver needs to access this firmware.
+
+A device driver which needs this can describe the firmware it needs
+using an efi_embedded_fw_desc struct:
+
+.. kernel-doc:: include/linux/efi_embedded_fw.h
+ :functions: efi_embedded_fw_desc
+
+The EFI embedded-fw code works by scanning all EFI_BOOT_SERVICES_CODE memory
+segments for an eight byte sequence matching prefix, if the prefix is found it
+then does a crc32 over length bytes and if that matches makes a copy of length
+bytes and adds that to its list with found firmwares.
+
+To avoid doing this somewhat expensive scan on all systems, dmi matching is
+used. Drivers are expected to export a dmi_system_id array, with each entries'
+driver_data pointing to an efi_embedded_fw_desc.
+
+To register this array with the efi-embedded-fw code, a driver needs to:
+
+1. Always be builtin to the kernel or store the dmi_system_id array in a
+ separate object file which always gets builtin.
+
+2. Add an extern declaration for the dmi_system_id array to
+ include/linux/efi_embedded_fw.h.
+
+3. Add the dmi_system_id array to the embedded_fw_table in
+ drivers/firmware/efi/embedded-firmware.c wrapped in a #ifdef testing that
+ the driver is being builtin.
+
+4. Add "select EFI_EMBEDDED_FIRMWARE if EFI_STUB" to its Kconfig entry.
+
+The request_firmware() function will always first try to load firmware with
+the specified name directly from the disk, so the EFI embedded-fw can always
+be overridden by placing a file under /lib/firmare.
+
+To make request_firmware() fallback to trying EFI embedded firmwares after this,
+the driver must set a boolean "efi-embedded-firmware" device-property on the
+device before passing it to request_firmware(). Note that this disables the
+usual usermodehelper fallback, so you may want to only set this on systems
+which match your dmi_system_id array.
+
+Once the device-property is set, the driver can use the regular
+request_firmware() function to get the firmware, using the name filled in
+in the efi_embedded_fw_desc.
+
+Note that:
+
+1. The code scanning for EFI embbedded-firmware runs near the end
+ of start_kernel(), just before calling rest_init(). For normal drivers and
+ subsystems using subsys_initcall() to register themselves this does not
+ matter. This means that code running earlier cannot use EFI
+ embbedded-firmware.
+
+2. ATM the EFI embedded-fw code assumes that firmwares always start at an offset
+ which is a multiple of 8 bytes, if this is not true for your case send in
+ a patch to fix this.
+
+3. ATM the EFI embedded-fw code only works on x86 because other archs free
+ EFI_BOOT_SERVICES_CODE before the EFI embedded-fw code gets a chance to
+ scan it.
+
+4. The current brute-force scanning of EFI_BOOT_SERVICES_CODE is an ad-hoc
+ brute-force solution. There has been discussion to use the PI spec's
+ Firmware Volume protocol. This has been rejected because the FV Protocol
+ relies on *internal* interfaces of PI spec, and:
+ 1. The The PI spec does not define firmware at all
+ 2. The internal interfaces of PI Spec does not guarantee any backward
+ compatibility. Any implementation details in FV may be subject to change,
+ and may vary system to system. Supporting the FV Protocol would be
+ difficult as it is purposely ambiguous.
diff --git a/drivers/base/firmware_loader/Makefile b/drivers/base/firmware_loader/Makefile
index a97eeb0be1d8..365a040995d3 100644
--- a/drivers/base/firmware_loader/Makefile
+++ b/drivers/base/firmware_loader/Makefile
@@ -5,3 +5,4 @@ obj-y := fallback_table.o
obj-$(CONFIG_FW_LOADER) += firmware_class.o
firmware_class-objs := main.o
firmware_class-$(CONFIG_FW_LOADER_USER_HELPER) += fallback.o
+firmware_class-$(CONFIG_EFI_EMBEDDED_FIRMWARE) += fallback_efi.o
diff --git a/drivers/base/firmware_loader/fallback.h b/drivers/base/firmware_loader/fallback.h
index 21063503e4ea..5103283873d5 100644
--- a/drivers/base/firmware_loader/fallback.h
+++ b/drivers/base/firmware_loader/fallback.h
@@ -66,4 +66,16 @@ static inline void unregister_sysfs_loader(void)
}
#endif /* CONFIG_FW_LOADER_USER_HELPER */

+#ifdef CONFIG_EFI_EMBEDDED_FIRMWARE
+int fw_get_efi_embedded_fw(struct device *dev, struct fw_priv *fw_priv,
+ enum fw_opt *opt_flags, int ret);
+#else
+static inline int fw_get_efi_embedded_fw(struct device *dev,
+ struct fw_priv *fw_priv,
+ enum fw_opt *opt_flags, int ret)
+{
+ return ret;
+}
+#endif /* CONFIG_EFI_EMBEDDED_FIRMWARE */
+
#endif /* __FIRMWARE_FALLBACK_H */
diff --git a/drivers/base/firmware_loader/fallback_efi.c b/drivers/base/firmware_loader/fallback_efi.c
new file mode 100644
index 000000000000..641598b8f746
--- /dev/null
+++ b/drivers/base/firmware_loader/fallback_efi.c
@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/efi_embedded_fw.h>
+#include <linux/property.h>
+#include <linux/security.h>
+#include <linux/vmalloc.h>
+
+#include "fallback.h"
+#include "firmware.h"
+
+int fw_get_efi_embedded_fw(struct device *dev, struct fw_priv *fw_priv,
+ enum fw_opt *opt_flags, int ret)
+{
+ size_t size, max = INT_MAX;
+ bool free_on_err = true;
+ int rc;
+
+ if (!dev)
+ return ret;
+
+ if (!device_property_read_bool(dev, "efi-embedded-firmware"))
+ return ret;
+
+ *opt_flags |= FW_OPT_NO_WARN | FW_OPT_NOCACHE | FW_OPT_NOFALLBACK;
+
+ rc = security_kernel_read_file(NULL, READING_FIRMWARE_EFI_EMBEDDED);
+ if (rc)
+ return rc;
+
+ /* Already populated data member means we're loading into a buffer */
+ if (fw_priv->data) {
+ max = fw_priv->allocated_size;
+ free_on_err = false;
+ }
+
+ rc = efi_get_embedded_fw(fw_priv->fw_name, &fw_priv->data, &size, max);
+ if (rc) {
+ dev_warn(dev, "Firmware %s not in EFI\n", fw_priv->fw_name);
+ return ret;
+ }
+
+ rc = security_kernel_post_read_file(NULL, fw_priv->data, size,
+ READING_FIRMWARE_EFI_EMBEDDED);
+ if (rc) {
+ if (free_on_err) {
+ vfree(fw_priv->data);
+ fw_priv->data = NULL;
+ }
+ return rc;
+ }
+
+ dev_dbg(dev, "using efi-embedded fw %s\n", fw_priv->fw_name);
+ fw_priv->size = size;
+ fw_state_done(fw_priv);
+ return 0;
+}
diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c
index 0943e7065e0e..9dab6efa057c 100644
--- a/drivers/base/firmware_loader/main.c
+++ b/drivers/base/firmware_loader/main.c
@@ -576,6 +576,8 @@ _request_firmware(const struct firmware **firmware_p, const char *name,
goto out;

ret = fw_get_filesystem_firmware(device, fw->priv);
+ if (ret)
+ ret = fw_get_efi_embedded_fw(device, fw->priv, &opt_flags, ret);
if (ret) {
if (!(opt_flags & FW_OPT_NO_WARN))
dev_warn(device,
diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index 3098410abad8..faefeff7fb34 100644
--- a/drivers/firmware/efi/Kconfig
+++ b/drivers/firmware/efi/Kconfig
@@ -164,6 +164,9 @@ config RESET_ATTACK_MITIGATION
have been evicted, since otherwise it will trigger even on clean
reboots.

+config EFI_EMBEDDED_FIRMWARE
+ bool
+
endmenu

config UEFI_CPER
diff --git a/drivers/firmware/efi/Makefile b/drivers/firmware/efi/Makefile
index cb805374f4bc..dde12cea8aac 100644
--- a/drivers/firmware/efi/Makefile
+++ b/drivers/firmware/efi/Makefile
@@ -25,6 +25,7 @@ obj-$(CONFIG_EFI_BOOTLOADER_CONTROL) += efibc.o
obj-$(CONFIG_EFI_TEST) += test/
obj-$(CONFIG_EFI_DEV_PATH_PARSER) += dev-path-parser.o
obj-$(CONFIG_APPLE_PROPERTIES) += apple-properties.o
+obj-$(CONFIG_EFI_EMBEDDED_FIRMWARE) += embedded-firmware.o

arm-obj-$(CONFIG_EFI) := arm-init.o arm-runtime.o
obj-$(CONFIG_ARM) += $(arm-obj-y)
diff --git a/drivers/firmware/efi/embedded-firmware.c b/drivers/firmware/efi/embedded-firmware.c
new file mode 100644
index 000000000000..244465a162c5
--- /dev/null
+++ b/drivers/firmware/efi/embedded-firmware.c
@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Support for extracting embedded firmware for peripherals from EFI code,
+ *
+ * Copyright (c) 2018 Hans de Goede <hdegoede@redhat.com>
+ */
+
+#include <crypto/sha.h>
+#include <linux/dmi.h>
+#include <linux/efi.h>
+#include <linux/efi_embedded_fw.h>
+#include <linux/io.h>
+#include <linux/types.h>
+#include <linux/vmalloc.h>
+
+struct embedded_fw {
+ struct list_head list;
+ const char *name;
+ void *data;
+ size_t length;
+};
+
+static LIST_HEAD(found_fw_list);
+
+static const struct dmi_system_id * const embedded_fw_table[] = {
+ NULL
+};
+
+/*
+ * Note the efi_check_for_embedded_firmwares() code currently makes the
+ * following 2 assumptions. This may needs to be revisited if embedded firmware
+ * is found where this is not true:
+ * 1) The firmware is only found in EFI_BOOT_SERVICES_CODE memory segments
+ * 2) The firmware always starts at an offset which is a multiple of 8 bytes
+ */
+static int __init efi_check_md_for_embedded_firmware(
+ efi_memory_desc_t *md, const struct efi_embedded_fw_desc *desc)
+{
+ const u64 prefix = *((u64 *)desc->prefix);
+ struct sha256_state sctx;
+ struct embedded_fw *fw;
+ u8 sha256[32];
+ u64 i, size;
+ void *map;
+
+ size = md->num_pages << EFI_PAGE_SHIFT;
+ map = memremap(md->phys_addr, size, MEMREMAP_WB);
+ if (!map) {
+ pr_err("Error mapping EFI mem at %#llx\n", md->phys_addr);
+ return -ENOMEM;
+ }
+
+ size -= desc->length;
+ for (i = 0; i < size; i += 8) {
+ u64 *mem = map + i;
+
+ if (*mem != prefix)
+ continue;
+
+ sha256_init_direct(&sctx);
+ sha256_update_direct(&sctx, map + i, desc->length);
+ sha256_final_direct(&sctx, sha256);
+ if (memcmp(sha256, desc->sha256, 32) == 0)
+ break;
+ }
+ if (i >= size) {
+ memunmap(map);
+ return -ENOENT;
+ }
+
+ pr_info("Found EFI embedded fw '%s'\n", desc->name);
+
+ fw = kmalloc(sizeof(*fw), GFP_KERNEL);
+ if (!fw) {
+ memunmap(map);
+ return -ENOMEM;
+ }
+
+ fw->data = kmemdup(map + i, desc->length, GFP_KERNEL);
+ memunmap(map);
+ if (!fw->data) {
+ kfree(fw);
+ return -ENOMEM;
+ }
+
+ fw->name = desc->name;
+ fw->length = desc->length;
+ list_add(&fw->list, &found_fw_list);
+
+ return 0;
+}
+
+void __init efi_check_for_embedded_firmwares(void)
+{
+ const struct efi_embedded_fw_desc *fw_desc;
+ const struct dmi_system_id *dmi_id;
+ efi_memory_desc_t *md;
+ int i, r;
+
+ for (i = 0; embedded_fw_table[i]; i++) {
+ dmi_id = dmi_first_match(embedded_fw_table[i]);
+ if (!dmi_id)
+ continue;
+
+ fw_desc = dmi_id->driver_data;
+ for_each_efi_memory_desc(md) {
+ if (md->type != EFI_BOOT_SERVICES_CODE)
+ continue;
+
+ r = efi_check_md_for_embedded_firmware(md, fw_desc);
+ if (r == 0)
+ break;
+ }
+ }
+}
+
+int efi_get_embedded_fw(const char *name, void **data, size_t *size,
+ size_t msize)
+{
+ struct embedded_fw *iter, *fw = NULL;
+ void *buf = *data;
+
+ list_for_each_entry(iter, &found_fw_list, list) {
+ if (strcmp(name, iter->name) == 0) {
+ fw = iter;
+ break;
+ }
+ }
+
+ if (!fw)
+ return -ENOENT;
+
+ if (msize && msize < fw->length)
+ return -EFBIG;
+
+ if (!buf) {
+ buf = vmalloc(fw->length);
+ if (!buf)
+ return -ENOMEM;
+ }
+
+ memcpy(buf, fw->data, fw->length);
+ *size = fw->length;
+ *data = buf;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(efi_get_embedded_fw);
diff --git a/include/linux/efi.h b/include/linux/efi.h
index d72358e892e7..657c98598bc2 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1575,6 +1575,12 @@ static inline void
efi_enable_reset_attack_mitigation(efi_system_table_t *sys_table_arg) { }
#endif

+#ifdef CONFIG_EFI_EMBEDDED_FIRMWARE
+void efi_check_for_embedded_firmwares(void);
+#else
+static inline void efi_check_for_embedded_firmwares(void) { }
+#endif
+
void efi_retrieve_tpm2_eventlog(efi_system_table_t *sys_table);

/*
diff --git a/include/linux/efi_embedded_fw.h b/include/linux/efi_embedded_fw.h
new file mode 100644
index 000000000000..6c8b04246fc3
--- /dev/null
+++ b/include/linux/efi_embedded_fw.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_EFI_EMBEDDED_FW_H
+#define _LINUX_EFI_EMBEDDED_FW_H
+
+#include <linux/mod_devicetable.h>
+
+/**
+ * struct efi_embedded_fw_desc - This struct is used by the EFI embedded-fw
+ * code to search for embedded firmwares.
+ *
+ * @name: Name to register the firmware with if found
+ * @prefix: First 8 bytes of the firmware
+ * @length: Length of the firmware in bytes including prefix
+ * @sha256: SHA256 of the firmware
+ */
+struct efi_embedded_fw_desc {
+ const char *name;
+ u8 prefix[8];
+ u32 length;
+ u8 sha256[32];
+};
+
+int efi_get_embedded_fw(const char *name, void **dat, size_t *sz, size_t msize);
+
+#endif
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 760d8da1b6c7..ebae9656d3bf 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2810,6 +2810,7 @@ extern int do_pipe_flags(int *, int);
id(UNKNOWN, unknown) \
id(FIRMWARE, firmware) \
id(FIRMWARE_PREALLOC_BUFFER, firmware) \
+ id(FIRMWARE_EFI_EMBEDDED, firmware) \
id(MODULE, kernel-module) \
id(KEXEC_IMAGE, kexec-image) \
id(KEXEC_INITRAMFS, kexec-initramfs) \
diff --git a/init/main.c b/init/main.c
index 3b4ada11ed52..98183aca5017 100644
--- a/init/main.c
+++ b/init/main.c
@@ -730,6 +730,9 @@ asmlinkage __visible void __init start_kernel(void)
arch_post_acpi_subsys_init();
sfi_init_late();

+ if (efi_enabled(EFI_PRESERVE_BS_REGIONS))
+ efi_check_for_embedded_firmwares();
+
if (efi_enabled(EFI_RUNTIME_SERVICES)) {
efi_free_boot_services();
}
--
2.17.0