Re: [PATCH 1/2] efi/libstub: add support for loading the initrd from a device path
From: Ard Biesheuvel <hidden>
Date: 2020-02-07 12:37:15
Also in:
linux-efi
On Fri, 7 Feb 2020 at 09:48, Laszlo Ersek [off-list ref] wrote:
On 02/06/20 15:03, Ard Biesheuvel wrote:quoted
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@kernel.org> --- drivers/firmware/efi/libstub/arm-stub.c | 16 +++-- drivers/firmware/efi/libstub/efi-stub-helper.c | 65 ++++++++++++++++++++ drivers/firmware/efi/libstub/efistub.h | 12 ++++ drivers/firmware/efi/libstub/x86-stub.c | 36 ++++++++++- include/linux/efi.h | 1 + 5 files changed, 123 insertions(+), 7 deletions(-)diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c index c7b091f50e55..1db943c1ba2b 100644 --- a/drivers/firmware/efi/libstub/arm-stub.c +++ b/drivers/firmware/efi/libstub/arm-stub.c@@ -157,6 +157,7 @@ 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;@@ -255,11 +256,18 @@ 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, ULONG_MAX, - efi_get_max_initrd_addr(dram_base, *image_addr), - &initrd_addr, &initrd_size); + max_addr = efi_get_max_initrd_addr(dram_base, *image_addr); + status = efi_load_initrd_devpath(&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, ULONG_MAX, max_addr, + &initrd_addr, &initrd_size);- So this seems to be fallback#1, for ARM, which looks good. - Are you sure you only want to fall back to the old method on EFI_NOT_FOUND? Wouldn't other return values from efi_load_initrd_devpath() justify that too? ... After checking the boot services called in efi_load_initrd_devpath(), this idea seems reasonable, but then I'd suggest documenting the significance of returning EFI_NOT_FOUND near the efi_load_initrd_devpath() function declaration, in "efistub.h".
Good point.
quoted
+ 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 8e60a39df3c5..eaf45ea749b3 100644 --- a/drivers/firmware/efi/libstub/efi-stub-helper.c +++ b/drivers/firmware/efi/libstub/efi-stub-helper.c@@ -323,3 +323,68 @@ void efi_char16_printk(efi_char16_t *str) efi_call_proto(efi_table_attr(efi_system_table(), con_out), output_string, str); } + +static const struct { + struct efi_vendor_dev_path vendor; + struct efi_generic_dev_path end; +} __packed initrd_devpath = { + { + 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_status_t efi_load_initrd_devpath(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; + + dp = (efi_device_path_protocol_t *)&initrd_devpath; + status = efi_bs_call(locate_device_path, &lf2_proto_guid, &dp, &handle); + if (status != EFI_SUCCESS) + return status; + + status = efi_bs_call(handle_protocol, handle, &lf2_proto_guid, + (void **)&lf2); + if (status != EFI_SUCCESS) + return status; + + initrd_size = 0; + status = efi_call_proto(lf2, load_file, + (efi_device_path_protocol_t *)&initrd_devpath, + false, &initrd_size, NULL);The second argument to EFI_LOAD_FILE2_PROTOCOL.LoadFile() is "FilePath", specified as "The device specific path of the file to load". This means it is supposed to be a (possibly empty) sequence of FILEPATH_DEVICE_PATH nodes, terminated by and "End Entire Device Path" node. See - 10.3.1 Generic Device Path Structures - 10.3.5.4 File Path Media Device Path in UEFI-2.8. And "initrd_devpath" is not a device path like that; instead it's the VenMedia device path that's installed on the handle that also carries our LoadFile2 instance.
OK, so you are saying this could be used to disambiguate which of several files you may want to load from the initrd GUIDed device path?
Now, I do see that this all theoretical here, as we don't expect the LoadFile2 instance that we've found via our special LINUX_EFI_INITRD_MEDIA_GUID VenMedia devpath to do *any* device-specific filename / pathname parsing. But in that case (i.e., given that the FilePath argument is totally irrelevant), I think it's much clearer if we simply pass an empty device path -- one that consists of a single "End Entire Device Path" node. I've checked, and your ArmVirtQemu patch ignores the FilePath argument too -- justifiedly so. I just think it's better to pass in a well-formed device path, rather than NULL. Because, the FilePath parameter is not marked OPTIONAL in the spec.
One thing that occurred to me is that we have to decide whether we want to support the '10.3.5.8 Relative Offset Range' device path node for this file, so that you could potentially load subranges of the file. I don't see a use case for it right now, though. But for my understanding, would the FilePath passed to LoadFile2 be 'Offset(...)+EndEntire' in that case? Or should it include the GUID device path node as well?
quoted
+ 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; + + status = efi_call_proto(lf2, load_file, + (efi_device_path_protocol_t *)&initrd_devpath, + false, &initrd_size, (void *)initrd_addr);Same here.quoted
+ if (status != EFI_SUCCESS) { + efi_free(initrd_size, initrd_addr); + return status; + } + + *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 99e93fd76ec5..fbf9f9442eed 100644 --- a/drivers/firmware/efi/libstub/efistub.h +++ b/drivers/firmware/efi/libstub/efistub.h@@ -566,6 +566,14 @@ union efi_load_file_protocol { } mixed_mode; }; +struct efi_vendor_dev_path { + u8 type; + u8 sub_type; + u16 length; + efi_guid_t vendorguid; + u8 vendordata[]; +} __packed; + void efi_pci_disable_bridge_busmaster(void); typedef efi_status_t (*efi_exit_boot_map_processing)(@@ -651,4 +659,8 @@ efi_status_t efi_load_initrd(efi_loaded_image_t *image, unsigned long *load_addr, unsigned long *load_size); +efi_status_t efi_load_initrd_devpath(unsigned long *load_addr, + unsigned long *load_size, + unsigned long max); + #endifdiff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c index f3e2ff31b624..7f38f95676dd 100644 --- a/drivers/firmware/efi/libstub/x86-stub.c +++ b/drivers/firmware/efi/libstub/x86-stub.c@@ -419,9 +419,20 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle, if (status != EFI_SUCCESS) goto fail2; - status = efi_load_initrd(image, hdr->initrd_addr_max, - above4g ? ULONG_MAX : hdr->initrd_addr_max, - &ramdisk_addr, &ramdisk_size); + /* + * The initrd loaded from the Linux initrd vendor device + * path should take precedence, as we don't want the + * [unverified] command line to override the initrd + * supplied by the [potentially verified] firmware. + */ + status = efi_load_initrd_devpath(&ramdisk_addr, &ramdisk_size, + above4g ? ULONG_MAX + : hdr->initrd_addr_max); + if (status == EFI_NOT_FOUND) + status = efi_load_initrd(image, hdr->initrd_addr_max, + above4g ? ULONG_MAX + : hdr->initrd_addr_max, + &ramdisk_addr, &ramdisk_size);Fallback#2, for x86, also looks good.quoted
if (status != EFI_SUCCESS) goto fail2; hdr->ramdisk_image = ramdisk_addr & 0xffffffff;@@ -732,6 +743,25 @@ struct boot_params *efi_main(efi_handle_t handle, ((u64)boot_params->ext_cmd_line_ptr << 32)); efi_parse_options((char *)cmdline_paddr); + if (!hdr->ramdisk_size && !boot_params->ext_ramdisk_size) { + unsigned long max = hdr->initrd_addr_max; + unsigned long addr, size; + + if (hdr->xloadflags & XLF_CAN_BE_LOADED_ABOVE_4G) + max = ULONG_MAX; + + status = efi_load_initrd_devpath(&addr, &size, max); + if (status == EFI_SUCCESS) { + hdr->ramdisk_image = (u32)addr; + hdr->ramdisk_size = (u32)size; + boot_params->ext_ramdisk_image = (u64)addr >> 32; + boot_params->ext_ramdisk_size = (u64)size >> 32; + } else if (status != EFI_NOT_FOUND) { + efi_printk("efi_load_initrd_devpath() failed!\n"); + goto fail; + } + } +No fallback here; this is not a replacement for efi_load_initrd(), but a brand new call. Why? (It's probably justified, I just don't know enough about the kernel.)
Yes, it is. efi_main() is called after efi_pe_entry() in the native PE boot case, and it is the only one being called when using the EFI handover protocol. So the expected new flow would be for efi_pe_entry() to run first and load the initrd, in which case this code would not run. However, it would be better to still support the EFI handover protocol when using this method of loading the initrd, not only for convenience, but also because we cannot call efi_pe_entry() when running in mixed mode. Interestingly, LoadImage() can be used to load 64-bit images on 32-bit EDK2 firmware today (and I have to check whether that holds for mixed mode Mac hardware as well), only StartImage() will fail. It all depends on whether we still care about mixed mode in the secure boot context going forward, but if we do, we may be able to use LoadImage() but then jump to this entry point (via startup_32 in head_32.S) So the bottom line is that we have to keep this entry point alive for the time being, but there is no reason to add initrd loading to it using the old method, since we can't support it very well in mixed mode (due to the prototypes of the protocols) and we don't support that now anyway.
quoted
/* * 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 9ccf313fe9de..75c83c322c40 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)Thanks, Laszlo
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