Re: [PATCH v8 00/13] arm64: kexec: add kexec_file_load() support

[AKASHI Takahiro]

Now my patch#2 to #5 were extracted from this patch set and put
into another separate one. Please see
http://lists.infradead.org/pipermail/linux-arm-kernel/2018-February/562195.htmlk

Thanks,
-Takahiro AKASHI

On Thu, Feb 22, 2018 at 08:17:19PM +0900, AKASHI Takahiro wrote:
> This is the eighth round of implementing kexec_file_load() support
> on arm64.[1]
> Most of the code is based on kexec-tools (along with some kernel code
> from x86, which also came from kexec-tools).
> 
> 
> This patch series enables us to
>   * load the kernel by specifying its file descriptor, instead of user-
>     filled buffer, at kexec_file_load() system call, and
>   * optionally verify its signature at load time for trusted boot.
> 
> Contrary to kexec_load() system call, as we discussed a long time ago,
> users may not be allowed to provide a device tree to the 2nd kernel
> explicitly, hence enforcing a dt blob of the first kernel to be re-used
> internally.
> 
> To use kexec_file_load() system call, instead of kexec_load(), at kexec
> command, '-s' option must be specified. See [2] for a necessary patch for
> kexec-tools.
> 
> To anaylize a generated crash dump file, use the latest master branch of
> crash utility[3] for v4.16-rc kernel. I always try to submit patches to
> fix any inconsistencies introduced in the latest kernel.
> 
> Regarding a kernel image verification, a signature must be presented
> along with the binary itself. A signature is basically a hash value
> calculated against the whole binary data and encrypted by a key which
> will be authenticated by one of the system's trusted certificates.
> Any attempt to read and load a to-be-kexec-ed kernel image through
> a system call will be checked and blocked if the binary's hash value
> doesn't match its associated signature.
> 
> There are two methods available now:
> 1. implementing arch-specific verification hook of kexec_file_load()
> 2. utilizing IMA(Integrity Measurement Architecture)[4] appraisal framework
> 
> Before my v7, I believed that my patch only supports (1) but am now
> confident that (2) comes free if IMA is enabled and properly configured.
> 
> 
> (1) Arch-specific verification hook
> If CONFIG_KEXEC_VERIFY_SIG is enabled, kexec_file_load() invokes an arch-
> defined (and hence file-format-specific) hook function to check for the
> validity of kernel binary.
> 
> On x86, a signature is embedded into a PE file (Microsoft's format) header
> of binary. Since arm64's "Image" can also be seen as a PE file as far as
> CONFIG_EFI is enabled, we adopt this format for kernel signing.  
> 
> As in the case of UEFI applications, we can create a signed kernel image:
>     $ sbsign --key ${KEY} --cert ${CERT} Image
> 
> You may want to use certs/signing_key.pem, which is intended to be used
> for module sigining (CONFIG_MODULE_SIG), as ${KEY} and ${CERT} for test
> purpose.
> 
> 
> (2) IMA appraisal-based
> IMA was first introduced in linux in order to meet TCG (Trusted Computing
> Group) requirement that all the sensitive files be *measured* before
> reading/executing them to detect any untrusted changes/modification.
> Then appraisal feature, which allows us to ensure the integrity of
> files and even prevent them from reading/executing, was added later.
> 
> Meanwhile, kexec_file_load() has been merged since v3.17 and evolved to
> enable IMA-appraisal type verification by the commit b804defe4297 ("kexec:
> replace call to copy_file_from_fd() with kernel version").
> 
> In this scheme, a signature will be stored in a extended file attribute,
> "security.ima" while a decryption key is hold in a dedicated keyring,
> ".ima" or "_ima".  All the necessary process of verification is confined
> in a secure API, kernel_read_file_from_fd(), called by kexec_file_load().
> 
>     Please note that powerpc is one of the two architectures now
>     supporting KEXEC_FILE, and that it wishes to exntend IMA,
>     where a signature may be appended to "vmlinux" file[5], like module
>     signing, instead of using an extended file attribute.
> 
> While IMA meant to be used with TPM (Trusted Platform Module) on secure
> platform, IMA is still usable without TPM. Here is an example procedure
> about how we can give it a try to run the feature using a self-signed
> root ca for demo/test purposes:
> 
>  1) Generate needed keys and certificates, following "Generate trusted
>     keys" section in README of ima-evm-utils[6].
> 
>  2) Build the kernel with the following kernel configurations, specifying
>     "ima-local-ca.pem" for CONFIG_SYSTEM_TRUSTED_KEYS:
> 	CONFIG_EXT4_FS_SECURITY
> 	CONFIG_INTEGRITY_SIGNATURE
> 	CONFIG_INTEGRITY_ASYMMETRIC_KEYS
> 	CONFIG_INTEGRITY_TRUSTED_KEYRING
> 	CONFIG_IMA
> 	CONFIG_IMA_WRITE_POLICY
> 	CONFIG_IMA_READ_POLICY
> 	CONFIG_IMA_APPRAISE
> 	CONFIG_IMA_APPRAISE_BOOTPARAM
> 	CONFIG_SYSTEM_TRUSTED_KEYS
>     Please note that CONFIG_KEXEC_VERIFY_SIG is not, actually should
>     not be, enabled.
> 
>  3) Sign(label) a kernel image binary to be kexec-ed on target filesystem:
>     $ evmctl ima_sign --key /path/to/private_key.pem /your/Image
> 
>  4) Add a command line parameter and boot the kernel:
>     ima_appraise=enforce
> 
>  On live system,
>  5) Set a security policy:
>     $ mount -t securityfs none /sys/kernel/security
>     $ echo "appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig" \
>       > /sys/kernel/security/ima/policy
> 
>  6) Add a key for ima:
>     $ keyctl padd asymmetric my_ima_key %:.ima < /path/to/x509_ima.der
>     (or evmctl import /path/to/x509_ima.der <ima_keyring_id>)
> 
>  7) Then try kexec as normal.
> 
> 
> Concerns(or future works):
> * Even if the kernel is configured with CONFIG_RANDOMIZE_BASE, the 2nd
>   kernel won't be placed at a randomized address. We will have to
>   add some boot code similar to efi-stub to implement the randomization.
> for approach (1),
> * While big-endian kernel can support kernel signing, I'm not sure that
>   Image can be recognized as in PE format because x86 standard only
>   defines little-endian-based format.
> * vmlinux support
> 
>   [1] http://git.linaro.org/people/takahiro.akashi/linux-aarch64.git
> 	branch:arm64/kexec_file
>   [2] http://git.linaro.org/people/takahiro.akashi/kexec-tools.git
> 	branch:arm64/kexec_file
>   [3] http://github.com/crash-utility/crash.git
>   [4] https://sourceforge.net/p/linux-ima/wiki/Home/
>   [5] http://lkml.iu.edu//hypermail/linux/kernel/1707.0/03669.html
>   [6] https://sourceforge.net/p/linux-ima/ima-evm-utils/ci/master/tree/
> 
> 
> Changes in v8 (Feb 22, 2018)
> * introduce ARCH_HAS_KEXEC_PURGATORY so that arm64 will be able to skip
>   purgatory
> * remove "ifdef CONFIG_X86_64" stuffs from a re-factored function,
>   prepare_elf64_headers(), making its interface more generic
>   (The original patch was split into two for easier reviews.)
> * modify cpu_soft_restart() so as to let the 2nd kernel jump into its entry
>   code directly without requiring purgatory in case of kexec_file_load
> * remove CONFIG_KEXEC_FILE_IMAGE_FMT and introduce
>   CONFIG_KEXEC_IMAGE_VERIFY_SIG, much similar to x86 but quite redundant
>   for now.
> * In addition, update/modify dependencies of KEXEC_IMAGE_VERIFY_SIG
> 
> Changes in v7 (Dec 4, 2017)
> * rebased to v4.15-rc2
> * re-organize the patch set to separate KEXEC_FILE_VERIFY_SIG-related
>   code from the others
> * revamp factored-out code in kernel/kexec_file.c due to the changes
>   in original x86 code
> * redefine walk_sys_ram_res_rev() prototype due to change of callback
>   type in the counterpart, walk_sys_ram_res()
> * make KEXEC_FILE_IMAGE_FMT defaut on if KEXEC_FILE selected
> 
> Changes in v6 (Oct 24, 2017)
> * fix a for-loop bug in _kexec_kernel_image_probe() per Julien
> 
> Changes in v5 (Oct 10, 2017)
> * fix kbuild errors around patch #3
> per Julien's comments,
> * fix a bug in walk_system_ram_res_rev() with some cleanup
> * modify fdt_setprop_range() to use vmalloc()
> * modify fill_property() to use memset()
> 
> Changes in v4 (Oct 2, 2017)
> * reinstate x86's arch_kexec_kernel_image_load()
> * rename weak arch_kexec_kernel_xxx() to _kexec_kernel_xxx() for
>   better re-use
> * constify kexec_file_loaders[]
> 
> Changes in v3 (Sep 15, 2017)
> * fix kbuild test error
> * factor out arch_kexec_kernel_*() & arch_kimage_file_post_load_cleanup()
> * remove CONFIG_CRASH_CORE guard from kexec_file.c
> * add vmapped kernel region to vmcore for gdb backtracing
>   (see prepare_elf64_headers())
> * merge asm/kexec_file.h into asm/kexec.h
> * and some cleanups
> 
> Changes in v2 (Sep 8, 2017)
> * move core-header-related functions from crash_core.c to kexec_file.c
> * drop hash-check code from purgatory
> * modify purgatory asm to remove arch_kexec_apply_relocations_add()
> * drop older kernel support
> * drop vmlinux support (at least, for this series)
> 
> 
> Patch #1 to #10 are essential part for KEXEC_FILE support
> (additionally allowing for IMA-based verification):
>   Patch #1 to #6 are all preparatory patches on generic side.
>   Patch #7 to #11 are to enable kexec_file_load on arm64.
> 
> Patch #12 to #13 are for KEXEC_VERIFY_SIG (arch-specific verification)
> support
> 
> AKASHI Takahiro (13):
>   resource: add walk_system_ram_res_rev()
>   kexec_file: make an use of purgatory optional
>   kexec_file,x86,powerpc: factor out kexec_file_ops functions
>   x86: kexec_file: factor out elf core header related functions
>   kexec_file, x86: move re-factored code to generic side
>   asm-generic: add kexec_file_load system call to unistd.h
>   arm64: kexec_file: invoke the kernel without purgatory
>   arm64: kexec_file: load initrd and device-tree
>   arm64: kexec_file: add crash dump support
>   arm64: kexec_file: add Image format support
>   arm64: kexec_file: enable KEXEC_FILE config
>   include: pe.h: remove message[] from mz header definition
>   arm64: kexec_file: enable KEXEC_VERIFY_SIG for Image
> 
>  arch/arm64/Kconfig                          |  34 +++
>  arch/arm64/include/asm/kexec.h              |  90 +++++++
>  arch/arm64/kernel/Makefile                  |   3 +-
>  arch/arm64/kernel/cpu-reset.S               |   6 +-
>  arch/arm64/kernel/kexec_image.c             | 105 ++++++++
>  arch/arm64/kernel/machine_kexec.c           |  11 +-
>  arch/arm64/kernel/machine_kexec_file.c      | 401 ++++++++++++++++++++++++++++
>  arch/arm64/kernel/relocate_kernel.S         |   3 +-
>  arch/powerpc/Kconfig                        |   3 +
>  arch/powerpc/include/asm/kexec.h            |   2 +-
>  arch/powerpc/kernel/kexec_elf_64.c          |   2 +-
>  arch/powerpc/kernel/machine_kexec_file_64.c |  39 +--
>  arch/x86/Kconfig                            |   3 +
>  arch/x86/include/asm/kexec-bzimage64.h      |   2 +-
>  arch/x86/kernel/crash.c                     | 332 +++++------------------
>  arch/x86/kernel/kexec-bzimage64.c           |   2 +-
>  arch/x86/kernel/machine_kexec_64.c          |  45 +---
>  include/linux/ioport.h                      |   3 +
>  include/linux/kexec.h                       |  34 ++-
>  include/linux/pe.h                          |   2 +-
>  include/uapi/asm-generic/unistd.h           |   4 +-
>  kernel/kexec_file.c                         | 238 ++++++++++++++++-
>  kernel/resource.c                           |  57 ++++
>  23 files changed, 1046 insertions(+), 375 deletions(-)
>  create mode 100644 arch/arm64/kernel/kexec_image.c
>  create mode 100644 arch/arm64/kernel/machine_kexec_file.c
> 
> -- 
> 2.16.2
>