Messages in this thread | | | From | David Howells <> | Subject | [GIT PULL] Load keys from signed PE binaries | Date | Thu, 21 Feb 2013 15:47:58 +0000 |
| |
Hi Linus,
Can you pull this patchset please?
It provides a facility by which keys can be added dynamically to a kernel that is running in secure-boot mode. To permit a key to be loaded under such a condition, we require that the new key be signed by a key that we already have (and trust) - where keys that we "already have" could include those embedded in the kernel, those in the UEFI database and those in cryptographic hardware.
Now, "keyctl add" will already handle X.509 certificates that are so signed, but Microsoft's signing service will only sign runnable EFI PE binaries.
We could require that the user reboot into the BIOS, add the key, and then switch back, but under some circumstances we want to be able to do this whilst the kernel is running.
The way we have come up with to get around this is to embed an X.509 certificate containing the key in a section called ".keylist" in an EFI PE binary and then get the binary signed by Microsoft. The key can then be passed to the kernel by passing the signed binary:
keyctl padd asymmetric "" {ID of .system_keyring} <pekey.efi.signed
This command executes the following steps:
(1) Parse the PE binary to locate the signature and the new key.
(2) Parse the PKCS#7 message in the PE binary.
(3) Parse the content of the PKCS#7 message which is in "Microsoft individual code signing form" (the mscode bits in my patches). This contains the PE binary digest type and the expected resultant digest value.
(4) Digest the signed parts of the PE binary and compare the digest obtained to the digest expected (obtained in step (3)).
(5) Digest the signed parts of the PKCS#7 message (which covers the content data used in step (3)).
(6) Verify the signature on the PKCS#7 message against one of the X.509 certificates it contains.
(7) Check the signatures on the chain of X.509 certificates in the PKCS#7 message as far as possible.
(8) Cross-reference the chain of X.509 certificates against the known keys the kernel already possesses, and if one is found, verify the signature of the nearest object to the PKCS#7 message that we can (or the PKCS#7 message itself) against the trusted key.
(9) Pass the X.509 certificate embedded in the message to the X.509 parser to be turned into a key.
To make this work, step (8) requires access to the .module_sign keyring, so this is separated from the module code to make the build dependencies simpler. It is also renamed to .system_keyring as it can then be generic.
To make life easier whilst testing, I got rid of the "extra_certificates" file and replaced it with a glob that just glues together all the "*.x509" files in the source and build root directories.
Since this requires the ability to add to .system_keyring, I have had to turn on WRITE permission for root - but so that _only_ trusted keys can be added, I've added two more flags in key->flags:
KEY_FLAG_TRUSTED - this key is trusted.
KEY_FLAG_TRUSTED_ONLY - only links to trusted keys can be made to this keyring.
I'm not sure that this is the best mechanism by which to filter keyring additions, but it's not currently visible to the user, and so can be changed. One thing we might want to consider is using X.509 extension fields to contain bitfields that indicate what is permitted of the key inside an X.509 certificate. These contribute to the X.509 cryptographic digest and so are secure.
What these patches then do is allow you to add new keys by signing them with a key a user will already have. There can be more than one source for these keys: firstly, there is a key built into the kernel for module signing purposes, and secondly, we have patches under development for extracting keys from the UEFI signature database.
Note: Though we don't actually execute the PE binary container to get at the key, the binary must be executable in the EFI environment for Microsoft to sign it.
The test wrapper I'm using is this:
#include <efi.h> #include <efilib.h>
EFI_STATUS efi_main (EFI_HANDLE image_handle, EFI_SYSTEM_TABLE *systab) { InitializeLib(image_handle, systab); Print(L"This program contains a list of public keys.\n"); return EFI_SUCCESS; }
extern __attribute__((section(".keylist"))) const uint8_t certificate_list[]; extern __attribute__((section(".keylist"))) const uint8_t certificate_list_end[]; asm(".section .keylist,\"a\"\n" "certificate_list:\n" ".incbin \"signing_key.x509\"\n" "certificate_list_end:" );
and is built from pekey.c by something like this:
CPPFLAGS := -nostdinc -I /usr/include/efi -I /usr/include/efi/x86_64
CFLAGS := -O2 -fpic \ -Wall -fshort-wchar -fno-strict-aliasing \ -fno-merge-constants -mno-red-zone
LDSCRIPT := /usr/lib64/gnuefi/elf_x86_64_efi.lds CRT0 := /usr/lib64/gnuefi/crt0-efi-x86_64.o X509 := magrathea KEY := /data/modsign/linux-modsign/signing_key.priv
pekey.efi.signed: pekey.efi pesign -i $< -o $@ -c $(X509) -p $(KEY) -s -f
pekey.efi: pekey.so objcopy \ -j .text -j .sdata -j .data -j .dynamic -j .dynsym -j .rel \ -j .rela -j .reloc -j .keylist --target=efi-app-x86_64 $< $@
pekey.so: pekey.o $(LD) -nostdlib -T $(LDSCRIPT) -shared -Bsymbolic $(CRT0) $< -o $@ \ -L /usr/lib64 -lefi -lgnuefi \ -L /usr/lib/gcc/x86_64-redhat-linux/4.7.2 -lgcc
pekey.o: pekey.c Makefile $(CC) $(CPPFLAGS) $(CFLAGS) -c $< -o $@
Signed-off-by: David Howells <dhowells@redhat.com> --- The following changes since commit 406089d01562f1e2bf9f089fd7637009ebaad589:
Merge tag 'trace-3.8-rc3-regression-fix' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace (2013-01-14 20:22:16 -0800)
are available in the git repository at:
git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-modsign.git tags/pekey-20130221
for you to fetch changes up to 4ea349d3bb1d3521b7df8dbf0e88fe41cd3c0683:
MODSIGN: Fix including certificate twice when the signing_key.x509 already exists (2013-02-21 14:11:40 +0000)
---------------------------------------------------------------- (from the branch description for devel-pekey local branch)
clone of "master" signed-pefile contained key
---------------------------------------------------------------- Chun-Yi Lee (1): MODSIGN: Fix including certificate twice when the signing_key.x509 already exists
David Howells (27): KEYS: Load *.x509 files into kernel keyring KEYS: Separate the kernel signature checking keyring from module signing KEYS: Add a 'trusted' flag and a 'trusted only' flag KEYS: Rename public key parameter name arrays KEYS: Move the algorithm pointer array from x509 to public_key.c KEYS: Store public key algo ID in public_key struct KEYS: Split public_key_verify_signature() and make available KEYS: Store public key algo ID in public_key_signature struct X.509: struct x509_certificate needs struct tm declaring X.509: Add bits needed for PKCS#7 X.509: Embed public_key_signature struct and create filler function X.509: Check the algorithm IDs obtained from parsing an X.509 certificate X.509: Handle certificates that lack an authorityKeyIdentifier field X.509: Export certificate parse and free functions PKCS#7: Implement a parser [RFC 2315] PKCS#7: Digest the data in a signed-data message PKCS#7: Find the right key in the PKCS#7 key list and verify the signature PKCS#7: Verify internal certificate chain PKCS#7: Find intersection between PKCS#7 message and known, trusted keys Provide PE binary definitions pefile: Parse a PE binary to find a key and a signature contained therein pefile: Strip the wrapper off of the cert data block pefile: Parse the presumed PKCS#7 content of the certificate blob pefile: Parse the "Microsoft individual code signing" data blob pefile: Digest the PE binary and compare to the PKCS#7 data PEFILE: Validate PKCS#7 trust chain PEFILE: Load the contained key if we consider the container to be validly signed
crypto/asymmetric_keys/Kconfig | 20 +- crypto/asymmetric_keys/Makefile | 30 ++ crypto/asymmetric_keys/mscode.asn1 | 28 ++ crypto/asymmetric_keys/mscode_parser.c | 110 +++++ crypto/asymmetric_keys/pefile_parser.c | 479 +++++++++++++++++++++ crypto/asymmetric_keys/pefile_parser.h | 36 ++ crypto/asymmetric_keys/pkcs7.asn1 | 127 ++++++ crypto/asymmetric_keys/pkcs7_parser.c | 326 ++++++++++++++ crypto/asymmetric_keys/pkcs7_parser.h | 72 ++++ crypto/asymmetric_keys/pkcs7_trust.c | 149 +++++++ crypto/asymmetric_keys/pkcs7_verify.c | 260 +++++++++++ crypto/asymmetric_keys/public_key.c | 60 ++- crypto/asymmetric_keys/public_key.h | 6 + crypto/asymmetric_keys/x509.asn1 | 2 +- crypto/asymmetric_keys/x509_cert_parser.c | 55 ++- crypto/asymmetric_keys/x509_parser.h | 28 +- crypto/asymmetric_keys/x509_public_key.c | 119 ++--- include/crypto/public_key.h | 9 +- include/keys/system_keyring.h | 23 + include/linux/key-type.h | 1 + include/linux/key.h | 3 + include/linux/oid_registry.h | 7 +- include/linux/pe.h | 448 +++++++++++++++++++ init/Kconfig | 13 + kernel/Makefile | 47 +- kernel/modsign_pubkey.c | 104 ----- kernel/module-internal.h | 2 - kernel/module_signing.c | 7 +- ...modsign_certificate.S => system_certificates.S} | 7 +- kernel/system_keyring.c | 103 +++++ security/keys/key.c | 8 + security/keys/keyring.c | 4 + 32 files changed, 2478 insertions(+), 215 deletions(-) create mode 100644 crypto/asymmetric_keys/mscode.asn1 create mode 100644 crypto/asymmetric_keys/mscode_parser.c create mode 100644 crypto/asymmetric_keys/pefile_parser.c create mode 100644 crypto/asymmetric_keys/pefile_parser.h create mode 100644 crypto/asymmetric_keys/pkcs7.asn1 create mode 100644 crypto/asymmetric_keys/pkcs7_parser.c create mode 100644 crypto/asymmetric_keys/pkcs7_parser.h create mode 100644 crypto/asymmetric_keys/pkcs7_trust.c create mode 100644 crypto/asymmetric_keys/pkcs7_verify.c create mode 100644 include/keys/system_keyring.h create mode 100644 include/linux/pe.h delete mode 100644 kernel/modsign_pubkey.c rename kernel/{modsign_certificate.S => system_certificates.S} (72%) create mode 100644 kernel/system_keyring.c
| |