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certs: Add EFI_CERT_X509_GUID support for dbx entries

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[ Upstream commit 56c5812623f95313f6a46fbf0beee7fa17c68bbf ]

This fixes CVE-2020-26541.

The Secure Boot Forbidden Signature Database, dbx, contains a list of now
revoked signatures and keys previously approved to boot with UEFI Secure
Boot enabled.  The dbx is capable of containing any number of
EFI_CERT_X509_SHA256_GUID, EFI_CERT_SHA256_GUID, and EFI_CERT_X509_GUID
entries.

Currently when EFI_CERT_X509_GUID are contained in the dbx, the entries are
skipped.

Add support for EFI_CERT_X509_GUID dbx entries. When a EFI_CERT_X509_GUID
is found, it is added as an asymmetrical key to the .blacklist keyring.
Anytime the .platform keyring is used, the keys in the .blacklist keyring
are referenced, if a matching key is found, the key will be rejected.

[DH: Made the following changes:
 - Added to have a config option to enable the facility.  This allows a
   Kconfig solution to make sure that pkcs7_validate_trust() is
   enabled.[1][2]
 - Moved the functions out from the middle of the blacklist functions.
 - Added kerneldoc comments.]

Signed-off-by: Eric Snowberg <[email protected]>
Signed-off-by: David Howells <[email protected]>
Reviewed-by: Jarkko Sakkinen <[email protected]>
cc: Randy Dunlap <[email protected]>
cc: Mickaël Salaün <[email protected]>
cc: Arnd Bergmann <[email protected]>
cc: [email protected]
Link: https://lore.kernel.org/r/[email protected]/ # rfc
Link: https://lore.kernel.org/r/[email protected]/ # v2
Link: https://lore.kernel.org/r/[email protected]/ # v3
Link: https://lore.kernel.org/r/[email protected]/ # v4
Link: https://lore.kernel.org/r/[email protected]/ # v5
Link: https://lore.kernel.org/r/161428672051.677100.11064981943343605138.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/161433310942.902181.4901864302675874242.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/161529605075.163428.14625520893961300757.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/[email protected]/ [1]
Link: https://lore.kernel.org/r/[email protected]/ [2]
Signed-off-by: Sasha Levin <[email protected]>
This commit is contained in:
Eric Snowberg 2021-01-22 13:10:51 -05:00 • committed by Sasha Levin
commit e20b90e4f8
6 changed files with 86 additions and 0 deletions
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9
certs/Kconfig
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@ -83,4 +83,13 @@ config SYSTEM_BLACKLIST_HASH_LIST
wrapper to incorporate the list into the kernel. Each <hash> should
be a string of hex digits.
config SYSTEM_REVOCATION_LIST
bool "Provide system-wide ring of revocation certificates"
depends on SYSTEM_BLACKLIST_KEYRING
depends on PKCS7_MESSAGE_PARSER=y
help
If set, this allows revocation certificates to be stored in the
blacklist keyring and implements a hook whereby a PKCS#7 message can
be checked to see if it matches such a certificate.
endmenu