Re: [PATCH RFC] Microcode late loading feature identification

[Mihai Carabas]

La 27.04.2020 10:27, Mihai Carabas a scris:
> This RFC patch set aims to provide a way to identify the modifications
> brought in by the new microcode updated at runtime (aka microcode late
> loading). This was debated last year and this patch set implements
> point #1 from Thomas Gleixner's idea:
> https://lore.kernel.org/lkml/alpine.DEB.2.21.1909062237580.1902@xxxxxxxxxxxxxxxxxxxxxxx/

+Ashok and Thomas to get a feedback from vendor side on file 
format/integration in the microcode blob and signature.

Thank you,
Mihai

> This patch set has the following patches:
>
> - patch 1 is introducing a new metadata file that comes with the microcode
> (provided by the CPU manufacture) that describes what modifications are
> done by loading the new microcode
>
> - patch 2 parses the metadata file and is verifying it against kernel
> policy. In this patch, as an RFC, as a kernel policy, it was imposed
> the rule of not allowing to remove any feature. If so, it won't be
> loaded a new microcode. The policy can be further extended and describe
> in different ways
>
> - patch 3 adds the documentation of the metadata file format
>
>
> How to test:
>
> - place metadata file in /lib/firmware/intel-ucode/ together with the
> microcode blob:
>
> [root@ovs108 ~]# ls -l /lib/firmware/intel-ucode
> total 96
> -rw-r--r--.   1 root root 34816 Mar 11 00:27 06-55-04
> -rw-r--r--.   1 root root    84 Mar 25 03:13 06-55-04.metadata
>
> The microcode blob can be taken from the microcode_ctl package.
>
> - after installing the kernel and rebooting the machine run "dracut -f
> --no-early-microcode" to create an initramfs without the microcode (and
> avoid early loading)
>
> - reboot
>
> - after rebooting issue: echo 1 > /sys/devices/system/cpu/microcode/reload
>
> [root@ovs108 ~]# cat /lib/firmware/intel-ucode/06-55-04.metadata
> m - 0x00000122
> c + 0x00000007 0x00 0x00000000 0x021cbfbb 0x00000000 0x00000000
>
> [root@ovs108 ~]# echo 1 > /sys/devices/system/cpu/microcode/reload
> [root@ovs108 ~]# dmesg | tail -2
> [ 1285.729841] microcode: Kernel policy does not allow to remove MSR: 122
> [ 1285.737144] microcode: kernel does not support the new microcode: intel-ucode/06-55-04
>
> [root@ovs108 ~]# cat /lib/firmware/intel-ucode/06-55-04.metadata
> m + 0x00000122
> c + 0x00000007 0x00 0x00000000 0x021cbfbb 0x00000000 0x00000000
> [root@ovs108 ~]# echo 1 > /sys/devices/system/cpu/microcode/reload
> [root@ovs108 ~]# dmesg | tail -10
> [ 1220.212415] microcode: updated to revision 0x2000065, date = 2019-09-05
> [ 1220.212645] microcode: Reload completed, microcode revision: 0x2000065
>
> Mihai Carabas (3):
>    x86: microcode: intel: read microcode metadata file
>    x86: microcode: intel: process microcode metadata
>    Documentation: x86: microcode: add description for metadata file
>
>   Documentation/x86/microcode.rst       | 36 +++++++++++++
>   arch/x86/kernel/cpu/microcode/intel.c | 97 +++++++++++++++++++++++++++++++++++
>   2 files changed, 133 insertions(+)