Re: [PATCH v5 2/5] efi: Add embedded peripheral firmware support

[Ard Biesheuvel]

Hi Hans,

One comment below, which I missed in review before.

On 29 April 2018 at 11:35, Hans de Goede <hdegoede@xxxxxxxxxx> 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@xxxxxxxxx>
> Suggested-by: Peter Jones <pjones@xxxxxxxxxx>
> Acked-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
> ---
[...]
> diff --git a/drivers/firmware/efi/embedded-firmware.c b/drivers/firmware/efi/embedded-firmware.c
> new file mode 100644
> index 000000000000..22a0f598b53d
> --- /dev/null
> +++ b/drivers/firmware/efi/embedded-firmware.c
> @@ -0,0 +1,149 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Support for extracting embedded firmware for peripherals from EFI code,
> + *
> + * Copyright (c) 2018 Hans de Goede <hdegoede@xxxxxxxxxx>
> + */
> +
> +#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;
> +

Please use the proper APIs here to cast u8* to u64*, i.e., either use
get_unaligned64() or use memcmp()

> +               /* 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;
> +}
> +EXPORT_SYMBOL_GPL(efi_get_embedded_fw);
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 791088360c1e..23e8a9c26ce2 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..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 b795aa341a3a..ab29775b35db 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -729,6 +729,9 @@ 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
>