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

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 05/04/2018 06:56 AM, Ard Biesheuvel wrote:
> Hi Hans,
> 
> One comment below, which I missed in review before.
> 
> On 29 April 2018 at 11:35, 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>
>> Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
>> ---
> [...]
>> 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@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;
>> +
> 
> Please use the proper APIs here to cast u8* to u64*, i.e., either use
> get_unaligned64() or use memcmp()

But we know the memory addresses are 64 bit aligned, so using
get_unaligned64 seems wrong, and I'm not sure if the compiler is
smart enough to optimize a memcmp to the single 64 bit integer comparison
we want done here.

Regards,

Hans

> 
>> +               /* 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
>>