Re: [PATCH v2 3/4] efi_capsule: Add a function to get the public key needed for capsule authentication

Simon,

On Mon, Apr 12, 2021 at 08:35:25PM +0530, Sughosh Ganu wrote:

Define a function which would be used in the scenario where the public key is stored on the platform's dtb. This dtb is concatenated with the u-boot binary during the build process. Platforms which have a different mechanism for getting the public key would define their own platform specific function under a different Kconfig symbol.

Signed-off-by: Sughosh Ganu sughosh.ganu@linaro.org

Changes since V1:

• Remove the weak function, and add the functionality to retrieve the public key under the config symbol CONFIG_EFI_PKEY_DTB_EMBED.

lib/efi_loader/efi_capsule.c | 43 +++++++++++++++++++++++++++++++----- 1 file changed, 38 insertions(+), 5 deletions(-)

diff --git a/lib/efi_loader/efi_capsule.c b/lib/efi_loader/efi_capsule.c index 2cc8f2dee0..d95e9377fe 100644 --- a/lib/efi_loader/efi_capsule.c +++ b/lib/efi_loader/efi_capsule.c @@ -14,10 +14,13 @@ #include <mapmem.h> #include <sort.h>

+#include <asm/global_data.h> #include <crypto/pkcs7.h> #include <crypto/pkcs7_parser.h> #include <linux/err.h>

+DECLARE_GLOBAL_DATA_PTR;

const efi_guid_t efi_guid_capsule_report = EFI_CAPSULE_REPORT_GUID; static const efi_guid_t efi_guid_firmware_management_capsule_id = EFI_FIRMWARE_MANAGEMENT_CAPSULE_ID_GUID; @@ -208,15 +211,45 @@ skip: const efi_guid_t efi_guid_capsule_root_cert_guid = EFI_FIRMWARE_MANAGEMENT_CAPSULE_ID_GUID;

-__weak int efi_get_public_key_data(void **pkey, efi_uintn_t *pkey_len) +#if defined(CONFIG_EFI_PKEY_DTB_EMBED) +int efi_get_public_key_data(void **pkey, efi_uintn_t *pkey_len) {

• /* The platform is supposed to provide

• * a method for getting the public key
  

• * stored in the form of efi signature
  

• * list
  

• /*

• * This is a function for retrieving the public key from the
  

• * platform's device tree. The platform's device tree has been
  

• * concatenated with the u-boot binary.
  

• * If a platform has a different mechanism to get the public
  

• * key, it can define it's own kconfig symbol and define a
  

• * function to retrieve the public key
  

  */
• const void *fdt_blob = gd->fdt_blob;
• const void *blob;
• const char *cnode_name = "capsule-key";
• const char *snode_name = "signature";

# Again, "key" is not the best word to describe the value.

The syntax assumed here in a device tree (control FDT) is; / { signature { capsule-key = "..."; }; ... };

"signature" node is already used as a directory to hold public keys for FIT image verification (vboot). (doc/uImage.FIT/signature.txt)

While it is unlikely that both EFI capsule authentication and FIT image authentication are enabled at the same time, I'm a bit concerned if the mixture of different contents might cause some confusion. For instance, "required-mode" which has nothing to do with UEFI capsule may exist directly under "signagture."

Do you have any thoughts?

-Takahiro Akashi

• int sig_node;
• int len;
• sig_node = fdt_subnode_offset(fdt_blob, 0, snode_name);
• if (sig_node < 0) {

• EFI_PRINT("Unable to get signature node offset\n");
  

• return -FDT_ERR_NOTFOUND;
  

• }
• blob = fdt_getprop(fdt_blob, sig_node, cnode_name, &len);
• if (!blob || len < 0) {

• EFI_PRINT("Unable to get capsule-key value\n");
  

• *pkey = NULL;
  

• *pkey_len = 0;
  

• return -FDT_ERR_NOTFOUND;
  

• }
• *pkey = (void *)blob;
• *pkey_len = len;
• return 0;

} +#endif /* CONFIG_EFI_PKEY_DTB_EMBED */

efi_status_t efi_capsule_authenticate(const void *capsule, efi_uintn_t capsule_size, void **image, efi_uintn_t *image_size) -- 2.17.1