[RFC V4 PATCH 00/15] Signature verification of hibernate snapshot

From: Lee, Chun-Yi
Date: Sat Sep 14 2013 - 20:57:02 EST

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Hi experts,

This patchset is the implementation for signature verification of hibernate
snapshot image. The origin idea is from Jiri Kosina: Let EFI bootloader
generate key-pair in UEFI secure boot environment, then pass it to kernel
for sign/verify S4 image.

Due to there have potential threat from the S4 image hacked, it may causes
kernel lost the trust in UEFI secure boot. Hacker attack the S4 snapshot
image in swap partition through whatever exploit from another trusted OS,
and the exploit may don't need physical access machine.

So, this patchset give the ability to kernel for parsing RSA private key
from EFI bootloader, then using the private key to generate the signature
of S4 snapshot image. Kernel put the signature to snapshot header, and
verify the signature when kernel try to recover snapshot image to memory.

How To Enable
==============

Set CONFIG_SNAPSHOT_VERIFICATION kernel config to enable. And you can also
choice which hash algorithm should snapshot be signed with. Then rebuild
kernel. This function depends on EFI_STUB.

Please note this function need UEFI bootloader's support to generate key-pair
in UEFI secure boot environment, e.g. shim. Current shim implementation by
Gary Lin:

Git:
https://github.com/lcp/shim/tree/s4-key-upstream
RPM:
https://build.opensuse.org/package/show/home:gary_lin:UEFI/shim

Please use the shim from above URL if you want to try. Please remember add
the hash of shim to db in UEFI BIOS because it didn't sign by Microsoft or
any OSV key.

The default behavior is taint kernel when signature check fail. If you want
direct fail whole hibernate snapshot restore procedure when signature check
does not pass, please use snapshot_sig_enforce kernel parameter or
CONFIG_EFI_SECURE_BOOT_SNAPSHOT_SIG_ENFORCE config.

If you want binding UEF secure boot with sig_enforce flag, then you can use
CONFIG_EFI_SECURE_BOOT_SNAPSHOT_SIG_ENFORCE config. The sig_enforce flag will
auto enabled when UEFI secure boot enabled.

Behavior
=========

The RSA key-pair are generated by EFI bootloader(e.g. shim) in UEFI secure
boot environment, then put private key to S4SignKey, public key to S4WakeKey
EFI variable. Kernel's behavior as following:

+ First, EFI stub kernel will check the following 2 EFI variable:
S4SignKey-fe141863-c070-478e-b8a3-878a5dc9ef21 [BootService]
S4WakeKey-fe141863-c070-478e-b8a3-878a5dc9ef21 [Runtime][Volatile]

S4SignKey and S4WakeKey is a RSA key-pair:
- S4SignKey is a private key that's used to generate signature of S4
snapshot.
The blob format of S4SignKey is PKCS#8 _uncompressed_ format, it should
packaged a RSA private key that's followed PKCS#1.

- S4WakeKey is a public key that's used to verify signature of S4
snapshot.
The blob format of S4WakeKey is X.509 format, it should packaged a RSA
public key that's followed PKCS#1.

+ EFI stub kernel will load the S4SignKey blob to RAM before ExitBootServices,
then copy to a memory page that's maintained by hibernate_key.c. This
private key will be used to sign snapshot when hibernate launched.

+ When sig_enforce flag set to TRUE, means force check verification pass:
- If kernel didn't find S4 key-pair, then kernel will block hibernate
functions including kernel space and userspace hibernate.
- If snapshot signature check fail when hibernate resume, the snapshot
restore procedure will fail and running normal boot process.

+ When sig_enforce flag set to FALSE, means not force the verification pass:
- If kernel didn't find S4 key-pair, then the hibernate function still
available. But kernel will be tainted after hibernate resume.
- If snapshot signature check fail when hibernate resume, the snapshot
restore procedure will allow continue. But kernel will be tainted.

On EFI bootloader side, the behavior as following:

+ EFI bootloader must generate RSA key-pair when:
- First time boot, bootloader generate key-pair when didn't find it.

- Bootloader need re-generate after found GenS4Key efi variable from OS:
GenS4Key-fe141863-c070-478e-b8a3-878a5dc9ef21 [Runtime][Non-Volatile]
The size of GenS4Key is 1 byte, OS(kernel or userland tool) will set it to
"1" for notify efi bootloader regenerate key-pair.

- If re-generate key-pair, bootloader need store the new public key to
EFI bootservices variable by itself, e.g. store to NextWakeKey variable
When system resumed from hibernate, bootloader need copy public key from
NextWakeKey to S4WakeKey, then kernel will use it to verify snapshot
image.

Implementation
==============

Whole implementation including 3 parts: shim, asymmetric keys and hibernate:

+ shim:
Current solution implemented by Gary Lin:
https://github.com/lcp/shim/tree/s4-key-upstream

Please use shim from the above URL if you want to try. Please remember add
this shim to db because it didn't sign by Microsoft or any OSV key.

+ Asymmetric keys:
This patchset implemented uncompressed PKCS#8 and RSA private key parser,
it also implement the signature generation operation of RSASSA-PKCS1-v_5
in PKCS#1 spec. [RFC3447 sec 8.2.2]
Set CONFIG_PKCS8_PRIVATE_KEY_INFO_PARSER=y will give kernel the abilities
to parsing private key in uncompressed PKCS#8 blob and generate signature.

+ Hibernate:
Set CONFIG_SNAPSHOT_VERIFICATION=y will enable the function of snapshot
signature generation and verification. I reserved 512 byes size in snapshot
header for store the signature that's generated from the digest with SHA
algorithms.

For adapt S4 signature check to secure boot, It Base on Matthew Garrett's 2
patches in "[PATCH] Add additional security checks when module loading is
restricted" series: https://lkml.org/lkml/2013/8/19/331
[PATCH 01/10] Add secure_modules() call
[PATCH V3 11/11] Add option to automatically enforce module signatures when in Secure Boot mode

Please help review this RFC patchset! Appreciate for any comments!

V4:
- Cleaned source code, use helper functions to reduce #ifdef chunk.
- Introduced sig_enforce flag, taint kernel when signature check fail.
- Use forward_info structure to maintain the empty of forward information and
new sign key from boot kernel to resume target kernel.
- Use efivar API to access S4WakeKey variable.
- Call set_key_regen_flag() to set key-pair regeneration flag in hibernate.c
and user.c

V3:
- Load S4 sign key before ExitBootServices in efi stub.
- In Makefile, moved hibernate_keys.o before hibernate.o for load S4 sign
key before check hibernate image. It makes sure the new sign key will be
transfer to resume target kernel.
- Set "depends on EFI_STUB" in Kconfig.

V2:
- Moved SNAPSHOT_VERIFICATION kernel config to earlier patch.
- Add dummy functions to simplify the ifdef check.
- Sent to opensuse-kernel@xxxxxxxxxxxx for review:
http://lists.opensuse.org/opensuse-kernel/2013-08/msg00025.html

V1:
- Internal review
- github:
https://github.com/joeyli/linux-s4sign/commits/devel-s4sign

Lee, Chun-Yi (15):
asymmetric keys: add interface and skeleton for implement signature
generation
asymmetric keys: implement EMSA_PKCS1-v1_5-ENCODE in rsa
asymmetric keys: separate the length checking of octet string from
RSA_I2OSP
asymmetric keys: implement OS2IP in rsa
asymmetric keys: implement RSASP1
asymmetric keys: support parsing PKCS #8 private key information
asymmetric keys: explicitly add the leading zero byte to encoded
message
Hibernate: introduced RSA key-pair to verify signature of snapshot
Hibernate: generate and verify signature of snapshot
Hibernate: Avoid S4 sign key data included in snapshot image
Hibernate: taint kernel when signature check fail
Hibernate: show the verification time for monitor performance
Hibernate: introduced SNAPSHOT_SIG_HASH config for select hash
algorithm
Hibernate: notify bootloader regenerate key-pair for snapshot
verification
Hibernate: adapt to UEFI secure boot with signature check

Documentation/kernel-parameters.txt | 7 +
arch/x86/Kconfig | 11 +
arch/x86/boot/compressed/eboot.c | 92 +++++++
arch/x86/include/asm/efi.h | 9 +
arch/x86/include/uapi/asm/bootparam.h | 1 +
arch/x86/kernel/setup.c | 7 +
arch/x86/platform/efi/efi.c | 68 +++++
crypto/asymmetric_keys/Kconfig | 11 +
crypto/asymmetric_keys/Makefile | 16 +
crypto/asymmetric_keys/pkcs8.asn1 | 19 ++
crypto/asymmetric_keys/pkcs8_info_parser.c | 152 ++++++++++
crypto/asymmetric_keys/pkcs8_parser.h | 23 ++
crypto/asymmetric_keys/pkcs8_private_key.c | 148 ++++++++++
crypto/asymmetric_keys/pkcs8_rsakey.asn1 | 29 ++
crypto/asymmetric_keys/private_key.h | 29 ++
crypto/asymmetric_keys/public_key.c | 32 +++
crypto/asymmetric_keys/rsa.c | 296 +++++++++++++++++++-
crypto/asymmetric_keys/signature.c | 28 ++
include/crypto/public_key.h | 28 ++
include/keys/asymmetric-subtype.h | 6 +
include/linux/efi.h | 25 ++
include/linux/kernel.h | 1 +
include/linux/suspend.h | 7 +
kernel/panic.c | 2 +
kernel/power/Kconfig | 77 +++++-
kernel/power/Makefile | 1 +
kernel/power/hibernate.c | 23 ++-
kernel/power/hibernate_keys.c | 410 ++++++++++++++++++++++++++++
kernel/power/main.c | 7 +-
kernel/power/power.h | 62 +++++
kernel/power/snapshot.c | 323 ++++++++++++++++++++++-
kernel/power/swap.c | 4 +
kernel/power/user.c | 14 +-
33 files changed, 1946 insertions(+), 22 deletions(-)
create mode 100644 crypto/asymmetric_keys/pkcs8.asn1
create mode 100644 crypto/asymmetric_keys/pkcs8_info_parser.c
create mode 100644 crypto/asymmetric_keys/pkcs8_parser.h
create mode 100644 crypto/asymmetric_keys/pkcs8_private_key.c
create mode 100644 crypto/asymmetric_keys/pkcs8_rsakey.asn1
create mode 100644 crypto/asymmetric_keys/private_key.h
create mode 100644 kernel/power/hibernate_keys.c

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Next message: Lee, Chun-Yi: "[PATCH V4 02/15] asymmetric keys: implement EMSA_PKCS1-v1_5-ENCODE in rsa"
Previous message: Andi Kleen: "Re: [RESEND PATCH v2 4/4] mm/hwpoison: fix the lack of onereference count against poisoned page"
Next in thread: Lee, Chun-Yi: "[PATCH V4 02/15] asymmetric keys: implement EMSA_PKCS1-v1_5-ENCODE in rsa"
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