linux-kernel - Re: [RFC PATCH 09/11] x86/microcode: Expose EUPDATESVN procedure via sysfs

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Date:   Wed, 9 Mar 2022 12:20:16 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Cathy Zhang <cathy.zhang@...el.com>
Cc:     linux-sgx@...r.kernel.org, x86@...nel.org, dave.hansen@...el.com,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 09/11] x86/microcode: Expose EUPDATESVN procedure via
 sysfs

On all your patches for the future: don't forget to Cc LKML.

On Wed, Mar 09, 2022 at 06:40:48PM +0800, Cathy Zhang wrote:
> EUPDATESVN is the SGX instruction which allows enclave attestation
> to include information about updated microcode without a reboot.
> 
> Microcode updates which affect SGX require two phases:
> 
> 1. Do the main microcode update
> 2. Make the new CPUSVN available for enclave attestation via
>    EUPDATESVN.
> 
> Before a EUPDATESVN can succeed, all enclave pages (EPC) must be
> marked as unused in the SGX metadata (EPCM). This operation destroys
> all preexisting SGX enclave data and metadata. This is by design and
> mitigates the impact of vulnerabilities that may have compromised
> enclaves or the SGX hardware itself prior to the update.
> 
> Signed-off-by: Cathy Zhang <cathy.zhang@...el.com>
> ---
>  arch/x86/include/asm/microcode.h     |  5 ++++
>  arch/x86/include/asm/sgx.h           |  5 ++++
>  arch/x86/kernel/cpu/microcode/core.c | 44 ++++++++++++++++++++++++++++

Why is all this code here at all?

What does that have *actually* to do with microcode loading?

AFAICT, you want to hook into microcode_check() which runs after the
microcode update and do your EUPDATESVN there...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette