linux-kernel - Re: [Patch v3 Part2 1/9] x86/microcode: Taint kernel only if microcode loading was successful

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Date:   Wed, 1 Feb 2023 13:47:58 -0800
From:   Ashok Raj <ashok.raj@...el.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Stefan Talpalaru <stefantalpalaru@...oo.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "Benjamin Herrenschmidt" <benh@...nel.crashing.org>,
        Jonathan Corbet <corbet@....net>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Peter Zilstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Martin Pohlack <mpohlack@...zon.de>,
        "Li, Aubrey" <aubrey.li@...el.com>, Ashok Raj <ashok.raj@...el.com>
Subject: Re: [Patch v3 Part2 1/9] x86/microcode: Taint kernel only if
 microcode loading was successful

Hi Boris,

While reworking I thought while at this, there is a chance to fix other
things.


On Wed, Feb 01, 2023 at 01:44:31PM +0100, Borislav Petkov wrote:
> On Tue, Jan 31, 2023 at 02:54:03PM -0800, Ashok Raj wrote:
> > It's not an error, only when request_microcode() returns UCODE_ERROR, should
> > it return -EINVAL,
> 
> So looking at ->request_microcode_fw(), it looks like we return
> UCODE_ERROR when something with parsing the blob has gone wrong. So I
> guess we can return something more fitting here to state that we failed
> while parsing the microcode blob from userspace: it is corrupted,
> truncated, what not.
> 
> Looking at the error codes, this:
> 
> #define ELIBBAD         80      /* Accessing a corrupted shared library */
> 
> seems fitting as it has "corrupted" blob in the definition. EBADF sounds
> fitting too. In any case, it should be a distinct error value which
> hints at what goes wrong.

Along the same lines, when check_online_cpu() should we return -EBUSY which
would distinguish between -EINVAL vs something different?

And we have a pr_err() to indicate not all CPUs are online. I suppose this
can be dropped in the same patch to fix return code? Since the error code
should be indicative of the problem?

pr_err("Not all CPUs online, aborting microcode update.\n");

> 
> > This shouldn't be noisy, but if you think this isn't needed, it can go
> > away.
> 
> I think all this preemptive development - it might make sense so let's
> do it - needs to stop. If there's an *actual* real use and need for it
> sure, but let's issue a printk just because is not one of them.
> 
> > When it fails due to current_rev < min_rev, Isn't it good to add indication
> > to user space that it didn't succeed? Thomas wanted these return codes, so
> > someone scripting can get a status after an attempt to load.
> 
> Return codes: yes. Random, flaky, potentially overwritten in the dmesg
> ring buffer error strings - nope. Soon someone will come along and say,
> "hey, don't touch those printk formats - my tool parses them and it'll
> break if you do." Yeah, right.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette