On 02/16/20 15:11, Ard Biesheuvel wrote:
> There are currently two ways to specify the initrd to be passed to the
> Linux kernel when booting via the EFI stub:
> - it can be passed as a initrd= command line option when doing a pure PE
> boot (as opposed to the EFI handover protocol that exists for x86)
> - otherwise, the bootloader or firmware can load the initrd into memory,
> and pass the address and size via the bootparams struct (x86) or
> device tree (ARM)
>
> In the first case, we are limited to loading from the same file system
> that the kernel was loaded from, and it is also problematic in a trusted
> boot context, given that we cannot easily protect the command line from
> tampering without either adding complicated white/blacklisting of boot
> arguments or locking down the command line altogether.
>
> In the second case, we force the bootloader to duplicate knowledge about
> the boot protocol which is already encoded in the stub, and which may be
> subject to change over time, e.g., bootparams struct definitions, memory
> allocation/alignment requirements for the placement of the initrd etc etc.
> In the ARM case, it also requires the bootloader to modify the hardware
> description provided by the firmware, as it is passed in the same file.
> On systems where the initrd is measured after loading, it creates a time
> window where the initrd contents might be manipulated in memory before
> handing over to the kernel.
>
> Address these concerns by adding support for loading the initrd into
> memory by invoking the EFI LoadFile2 protocol installed on a vendor
> GUIDed device path that specifically designates a Linux initrd.
> This addresses the above concerns, by putting the EFI stub in charge of
> placement in memory and of passing the base and size to the kernel proper
> (via whatever means it desires) while still leaving it up to the firmware
> or bootloader to obtain the file contents, potentially from other file
> systems than the one the kernel itself was loaded from. On platforms that
> implement measured boot, it permits the firmware to take the measurement
> right before the kernel actually consumes the contents.
>
> Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> ---
> drivers/firmware/efi/libstub/arm-stub.c | 15 +++-
> drivers/firmware/efi/libstub/efi-stub-helper.c | 82 ++++++++++++++++++++
> drivers/firmware/efi/libstub/efistub.h | 4 +
> drivers/firmware/efi/libstub/x86-stub.c | 23 ++++++
> include/linux/efi.h | 1 +
> 5 files changed, 122 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
> index 2edc673ea06c..4bae620b95b9 100644
> --- a/drivers/firmware/efi/libstub/arm-stub.c
> +++ b/drivers/firmware/efi/libstub/arm-stub.c
> @@ -160,6 +160,7 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table_arg,
> enum efi_secureboot_mode secure_boot;
> struct screen_info *si;
> efi_properties_table_t *prop_tbl;
> + unsigned long max_addr;
>
> sys_table = sys_table_arg;
>
> @@ -258,10 +259,18 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table_arg,
> if (!fdt_addr)
> pr_efi("Generating empty DTB\n");
>
> - status = efi_load_initrd(image, &initrd_addr, &initrd_size, ULONG_MAX,
> - efi_get_max_initrd_addr(dram_base, *image_addr));
> + max_addr = efi_get_max_initrd_addr(dram_base, *image_addr);
> + status = efi_load_initrd_dev_path(&initrd_addr, &initrd_size, max_addr);
> + if (status == EFI_SUCCESS) {
> + pr_efi("Loaded initrd from LINUX_EFI_INITRD_MEDIA_GUID device path\n");
> + } else if (status == EFI_NOT_FOUND) {
> + status = efi_load_initrd(image, &initrd_addr, &initrd_size,
> + ULONG_MAX, max_addr);
> + if (status == EFI_SUCCESS)
> + pr_efi("Loaded initrd from command line option\n");
> + }
> if (status != EFI_SUCCESS)
> - pr_efi_err("Failed initrd from command line!\n");
> + pr_efi_err("Failed to load initrd!\n");
>
> efi_random_get_seed();
>
> diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
> index 49008ac88b63..e37afe2c752e 100644
> --- a/drivers/firmware/efi/libstub/efi-stub-helper.c
> +++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
> @@ -299,3 +299,85 @@ void efi_char16_printk(efi_char16_t *str)
> efi_call_proto(efi_table_attr(efi_system_table(), con_out),
> output_string, str);
> }
> +
> +/*
> + * The LINUX_EFI_INITRD_MEDIA_GUID vendor media device path below provides a way
> + * for the firmware or bootloader to expose the initrd data directly to the stub
> + * via the trivial LoadFile2 protocol, which is defined in the UEFI spec, and is
> + * very easy to implement. It is a simple Linux initrd specific conduit between
> + * kernel and firmware, allowing us to put the EFI stub (being part of the
> + * kernel) in charge of where and when to load the initrd, while leaving it up
> + * to the firmware to decide whether it needs to expose its filesystem hierarchy
> + * via EFI protocols.
> + */
> +static const struct {
> + struct efi_vendor_dev_path vendor;
> + struct efi_generic_dev_path end;
> +} __packed initrd_dev_path = {
> + {
> + EFI_DEV_MEDIA,
> + EFI_DEV_MEDIA_VENDOR,
> + sizeof(struct efi_vendor_dev_path),
> + LINUX_EFI_INITRD_MEDIA_GUID
> + }, {
> + EFI_DEV_END_PATH,
> + EFI_DEV_END_ENTIRE,
> + sizeof(struct efi_generic_dev_path)
> + }
> +};
> +
> +/**
> + * efi_load_initrd_dev_path - load the initrd from the Linux initrd device path
> + * @load_addr: pointer to store the address where the initrd was loaded
> + * @load_size: pointer to store the size of the loaded initrd
> + * @max: upper limit for the initrd memory allocation
> + * @return: %EFI_SUCCESS if the initrd was loaded successfully, in which case
> + * @load_addr and @load_size are assigned accordingly
> + * %EFI_NOT_FOUND if no LoadFile2 protocol exists on the initrd
> + * device path
> + * %EFI_LOAD_ERROR in all other cases
[*]
> + */
> +efi_status_t efi_load_initrd_dev_path(unsigned long *load_addr,
> + unsigned long *load_size,
> + unsigned long max)
> +{
> + efi_guid_t lf2_proto_guid = EFI_LOAD_FILE2_PROTOCOL_GUID;
> + efi_device_path_protocol_t *dp;
> + efi_load_file2_protocol_t *lf2;
> + unsigned long initrd_addr;
> + unsigned long initrd_size;
> + efi_handle_t handle;
> + efi_status_t status;
> +
> + if (!load_addr || !load_size)
> + return EFI_INVALID_PARAMETER;
Doesn't return EFI_LOAD_ERROR.
> +
> + dp = (efi_device_path_protocol_t *)&initrd_dev_path;
> + status = efi_bs_call(locate_device_path, &lf2_proto_guid, &dp, &handle);
> + if (status != EFI_SUCCESS)
> + return status;
Seems safe (the only plausible error could be EFI_NOT_FOUND).
> +
> + status = efi_bs_call(handle_protocol, handle, &lf2_proto_guid,
> + (void **)&lf2);
> + if (status != EFI_SUCCESS)
> + return status;
Interesting case; this should never fail... but note, if it does, it
returns EFI_UNSUPPORTED, not EFI_NOT_FOUND (if the protocol is missing
from the handle).
> +
> + status = efi_call_proto(lf2, load_file, dp, false, &initrd_size, NULL);
> + if (status != EFI_BUFFER_TOO_SMALL)
> + return EFI_LOAD_ERROR;
> +
> + status = efi_allocate_pages(initrd_size, &initrd_addr, max);
> + if (status != EFI_SUCCESS)
> + return status;
Not sure about the efi_allocate_pages() wrapper (?); the UEFI service
could return EFI_OUT_OF_RESOURCES.
Looks OK to me otherwise.
(... I'm a bit doubtful of passing and End node to LF2 rather than a
filepath node with "" for pathname, but it's an LF2 on our own vendor
path, so I guess we dictate what we accept.)
Thanks
Laszlo
> +
> + status = efi_call_proto(lf2, load_file, dp, false, &initrd_size,
> + (void *)initrd_addr);
> + if (status != EFI_SUCCESS) {
> + efi_free(initrd_size, initrd_addr);
> + return EFI_LOAD_ERROR;
> + }
> +
> + *load_addr = initrd_addr;
> + *load_size = initrd_size;
> + return EFI_SUCCESS;
> +}
> diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
> index 34fe3fad042f..b58cb2c4474e 100644
> --- a/drivers/firmware/efi/libstub/efistub.h
> +++ b/drivers/firmware/efi/libstub/efistub.h
> @@ -640,4 +640,8 @@ efi_status_t efi_load_initrd(efi_loaded_image_t *image,
> unsigned long soft_limit,
> unsigned long hard_limit);
>
> +efi_status_t efi_load_initrd_dev_path(unsigned long *load_addr,
> + unsigned long *load_size,
> + unsigned long max);
> +
> #endif
> diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
> index 681b620d8d40..16bf4ed21f1f 100644
> --- a/drivers/firmware/efi/libstub/x86-stub.c
> +++ b/drivers/firmware/efi/libstub/x86-stub.c
> @@ -699,9 +699,14 @@ struct boot_params *efi_main(efi_handle_t handle,
> {
> unsigned long bzimage_addr = (unsigned long)startup_32;
> struct setup_header *hdr = &boot_params->hdr;
> + unsigned long max_addr = hdr->initrd_addr_max;
> + unsigned long initrd_addr, initrd_size;
> efi_status_t status;
> unsigned long cmdline_paddr;
>
> + if (hdr->xloadflags & XLF_CAN_BE_LOADED_ABOVE_4G)
> + max_addr = ULONG_MAX;
> +
> sys_table = sys_table_arg;
>
> /* Check if we were booted by the EFI firmware */
> @@ -734,6 +739,24 @@ struct boot_params *efi_main(efi_handle_t handle,
> ((u64)boot_params->ext_cmd_line_ptr << 32));
> efi_parse_options((char *)cmdline_paddr);
>
> + /*
> + * At this point, an initrd may already have been loaded, either by
> + * the bootloader and passed via bootparams, or loaded from a initrd=
> + * command line option by efi_pe_entry() above. In either case, we
> + * permit an initrd loaded from the LINUX_EFI_INITRD_MEDIA_GUID device
> + * path to supersede it.
> + */
> + status = efi_load_initrd_dev_path(&initrd_addr, &initrd_size, max_addr);
> + if (status == EFI_SUCCESS) {
> + hdr->ramdisk_image = (u32)initrd_addr;
> + hdr->ramdisk_size = (u32)initrd_size;
> + boot_params->ext_ramdisk_image = (u64)initrd_addr >> 32;
> + boot_params->ext_ramdisk_size = (u64)initrd_size >> 32;
> + } else if (status != EFI_NOT_FOUND) {
> + efi_printk("efi_load_initrd_dev_path() failed!\n");
> + goto fail;
> + }
> +
> /*
> * If the boot loader gave us a value for secure_boot then we use that,
> * otherwise we ask the BIOS.
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 0976e57b4caa..1bf482daa22d 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -353,6 +353,7 @@ void efi_native_runtime_setup(void);
> #define LINUX_EFI_TPM_EVENT_LOG_GUID EFI_GUID(0xb7799cb0, 0xeca2, 0x4943, 0x96, 0x67, 0x1f, 0xae, 0x07, 0xb7, 0x47, 0xfa)
> #define LINUX_EFI_TPM_FINAL_LOG_GUID EFI_GUID(0x1e2ed096, 0x30e2, 0x4254, 0xbd, 0x89, 0x86, 0x3b, 0xbe, 0xf8, 0x23, 0x25)
> #define LINUX_EFI_MEMRESERVE_TABLE_GUID EFI_GUID(0x888eb0c6, 0x8ede, 0x4ff5, 0xa8, 0xf0, 0x9a, 0xee, 0x5c, 0xb9, 0x77, 0xc2)
> +#define LINUX_EFI_INITRD_MEDIA_GUID EFI_GUID(0x5568e427, 0x68fc, 0x4f3d, 0xac, 0x74, 0xca, 0x55, 0x52, 0x31, 0xcc, 0x68)
>
> /* OEM GUIDs */
> #define DELLEMC_EFI_RCI2_TABLE_GUID EFI_GUID(0x2d9f28a2, 0xa886, 0x456a, 0x97, 0xa8, 0xf1, 0x1e, 0xf2, 0x4f, 0xf4, 0x55)
>
