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Subject: Re: [PATCH v3 2/5] efi: Add embedded peripheral firmware support
To:     Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc:     Darren Hart <dvhart@infradead.org>,
        Andy Shevchenko <andy@infradead.org>,
        "Luis R . Rodriguez" <mcgrof@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H . Peter Anvin" <hpa@zytor.com>,
        platform-driver-x86@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Jones <pjones@redhat.com>,
        Dave Olsthoorn <dave@bewaar.me>,
        Will Deacon <will.deacon@arm.com>,
        Andy Lutomirski <luto@kernel.org>,
        Matt Fleming <matt@codeblueprint.co.uk>,
        David Howells <dhowells@redhat.com>,
        Mimi Zohar <zohar@linux.vnet.ibm.com>,
        Josh Triplett <josh@joshtriplett.org>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Martin Fuzzey <mfuzzey@parkeon.com>,
        Kees Cook <keescook@chromium.org>,
        Kalle Valo <kvalo@codeaurora.org>,
        Arend Van Spriel <arend.vanspriel@broadcom.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Nicolas Broeking <nbroeking@me.com>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Torsten Duwe <duwe@suse.de>,
        the arch/x86 maintainers <x86@kernel.org>,
        linux-efi@vger.kernel.org
References: <20180408174014.21908-1-hdegoede@redhat.com>
 <20180408174014.21908-3-hdegoede@redhat.com>
 <CAKv+Gu9UqWrcok7xatMu8WVZgKO-1vGkT_XCtbHoAZBrqh8b8g@mail.gmail.com>
From:   Hans de Goede <hdegoede@redhat.com>
Message-ID: <944f763c-5487-7930-a789-fd9718de3c7b@redhat.com>
Date:   Tue, 24 Apr 2018 15:17:09 +0200
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Hi,

On 16-04-18 10:28, Ard Biesheuvel wrote:
> On 8 April 2018 at 19:40, Hans de Goede <hdegoede@redhat.com> wrote:
>> 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>
>> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
>> ---
>> 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
>>
>> Changes in v3:
>> -Fix the docs using "efi-embedded-fw" as property name instead of
>>   "efi-embedded-firmware"
>> ---
>>   .../driver-api/firmware/request_firmware.rst  |  70 +++++++++
>>   drivers/base/firmware_loader/main.c           |  33 ++++
>>   drivers/firmware/efi/Kconfig                  |   6 +
>>   drivers/firmware/efi/Makefile                 |   1 +
>>   drivers/firmware/efi/embedded-firmware.c      | 148 ++++++++++++++++++
>>   include/linux/efi.h                           |   6 +
>>   include/linux/efi_embedded_fw.h               |  25 +++
>>   init/main.c                                   |   1 +
>>   8 files changed, 290 insertions(+)
>>   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 20f21ed427a5..189b02f815c9 100644
>> --- a/Documentation/driver-api/firmware/request_firmware.rst
>> +++ b/Documentation/driver-api/firmware/request_firmware.rst
>> @@ -68,3 +68,73 @@ 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. On some systems the embedded-firmware may be accessible through the
>> +   EFI_FIRMWARE_VOLUME_PROTOCOL if this is the case this may be a better way
>> +   to access the firmware files.
> 
> EFI_FIRMWARE_VOLUME_PROTOCOL is not a UEFI protocol, so I'd prefer it
> if we just drop this point altogether.

Hmm, there have been requests for me to document this because it might be
an interesting approach in some cases, anyways dropped for v4.

>> diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c
>> index eb34089e4299..1aa42f147415 100644
>> --- a/drivers/base/firmware_loader/main.c
>> +++ b/drivers/base/firmware_loader/main.c
>> @@ -33,6 +33,8 @@
>>   #include <linux/syscore_ops.h>
>>   #include <linux/reboot.h>
>>   #include <linux/security.h>
>> +#include <linux/efi_embedded_fw.h>
>> +#include <linux/property.h>
>>
>>   #include <generated/utsrelease.h>
>>
>> @@ -340,6 +342,28 @@ fw_get_filesystem_firmware(struct device *device, struct fw_priv *fw_priv)
>>          return rc;
>>   }
>>
>> +#ifdef CONFIG_EFI_EMBEDDED_FIRMWARE
>> +static int
>> +fw_get_efi_embedded_fw(struct device *dev, struct fw_priv *fw_priv, int ret)
>> +{
>> +       size_t size;
>> +       int rc;
>> +
>> +       rc = efi_get_embedded_fw(fw_priv->fw_name, &fw_priv->data, &size,
>> +                                fw_priv->data ? fw_priv->allocated_size : 0);
>> +       if (rc == 0) {
>> +               dev_dbg(dev, "using efi-embedded fw %s\n", fw_priv->fw_name);
>> +               fw_priv->size = size;
>> +               fw_state_done(fw_priv);
>> +               ret = 0;
>> +       } else {
>> +               dev_warn(dev, "Firmware %s not in EFI\n", fw_priv->fw_name);
>> +       }
>> +
>> +       return ret;
>> +}
>> +#endif
>> +
>>   /* firmware holds the ownership of pages */
>>   static void firmware_free_data(const struct firmware *fw)
>>   {
>> @@ -576,6 +600,15 @@ _request_firmware(const struct firmware **firmware_p, const char *name,
>>                  goto out;
>>
>>          ret = fw_get_filesystem_firmware(device, fw->priv);
>> +#ifdef CONFIG_EFI_EMBEDDED_FIRMWARE
>> +       if (ret && device &&
>> +           device_property_read_bool(device, "efi-embedded-firmware")) {
>> +               ret = fw_get_efi_embedded_fw(device, fw->priv, ret);
>> +               if (ret == 0)
>> +                       ret = assign_fw(fw, device, opt_flags | FW_OPT_NOCACHE);
>> +               goto out;
>> +       }
>> +#endif
>>          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..efb190f5c157 100644
>> --- a/drivers/firmware/efi/Kconfig
>> +++ b/drivers/firmware/efi/Kconfig
>> @@ -164,6 +164,12 @@ config RESET_ATTACK_MITIGATION
>>            have been evicted, since otherwise it will trigger even on clean
>>            reboots.
>>
>> +config EFI_EMBEDDED_FIRMWARE
>> +       # This needs boot-services-code to be kept around till after mm_init()
>> +       # so make this X86 only for now
>> +       depends on EFI_STUB && X86
>> +       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..cb57225a340d
>> --- /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 <linux/crc32.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)
>> +{
>> +       struct embedded_fw *fw;
>> +       u64 i, size;
>> +       u32 crc;
>> +       u8 *mem;
>> +
>> +       size = md->num_pages << EFI_PAGE_SHIFT;
>> +       mem = memremap(md->phys_addr, size, MEMREMAP_WB);
>> +       if (!mem) {
>> +               pr_err("Error mapping EFI mem at %#llx\n", md->phys_addr);
>> +               return -ENOMEM;
>> +       }
>> +
>> +       size -= desc->length;
>> +       for (i = 0; i < size; i += 8) {
>> +               if (*((u64 *)(mem + i)) != *((u64 *)desc->prefix))
>> +                       continue;
>> +
>> +               /* Seed with ~0, invert to match crc32 userspace utility */
>> +               crc = ~crc32(~0, mem + i, desc->length);
>> +               if (crc == desc->crc)
>> +                       break;
>> +       }
>> +
>> +       memunmap(mem);
>> +
>> +       if (i >= size)
>> +               return -ENOENT;
>> +
>> +       pr_info("Found EFI embedded fw '%s' crc %08x\n", desc->name, desc->crc);
>> +
>> +       fw = kmalloc(sizeof(*fw), GFP_KERNEL);
>> +       if (!fw)
>> +               return -ENOMEM;
>> +
>> +       mem = memremap(md->phys_addr + i, desc->length, MEMREMAP_WB);
>> +       if (!mem) {
>> +               pr_err("Error mapping embedded firmware\n");
>> +               goto error_free_fw;
>> +       }
>> +       fw->data = kmemdup(mem, desc->length, GFP_KERNEL);
>> +       memunmap(mem);
>> +       if (!fw->data)
>> +               goto error_free_fw;
>> +
>> +       fw->name = desc->name;
>> +       fw->length = desc->length;
>> +       list_add(&fw->list, &found_fw_list);
>> +
>> +       return 0;
>> +
>> +error_free_fw:
>> +       kfree(fw);
>> +       return -ENOMEM;
>> +}
>> +
>> +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;
>> +}
>> diff --git a/include/linux/efi.h b/include/linux/efi.h
>> index f5083aa72eae..3847323ace2f 100644
>> --- a/include/linux/efi.h
>> +++ b/include/linux/efi.h
>> @@ -1572,6 +1572,12 @@ 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..0f7d4df3f57a
>> --- /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
>> + * @crc:    Inverted little endian Ethernet style CRC32, with 0xffffffff seed
>> + */
>> +struct efi_embedded_fw_desc {
>> +       const char *name;
>> +       u8 prefix[8];
>> +       u32 length;
>> +       u32 crc;
>> +};
>> +
>> +int efi_get_embedded_fw(const char *name, void **dat, size_t *sz, size_t msize);
>> +
>> +#endif
>> diff --git a/init/main.c b/init/main.c
>> index 21efbf6ace93..51dc2981d229 100644
>> --- a/init/main.c
>> +++ b/init/main.c
>> @@ -710,6 +710,7 @@ asmlinkage __visible void __init start_kernel(void)
>>          sfi_init_late();
>>
>>          if (efi_enabled(EFI_RUNTIME_SERVICES)) {
>> +               efi_check_for_embedded_firmwares();
> 
> Should this depend on EFI runtime services? I don't see why it should
> matter whether you have access to variables or the EFI rtc services.
> 
> If the regions are not reserved in the first place in that case, I'd
> rather fix that properly. (see comment re new EFI_xxx flag in previous
> mail)

Ok, I've put this under an "if (efi_enabled(EFI_BOOT_SERVICES))"
check for v4.

Regards,

Hans