linux-kernel - Re: [PATCH] x86/microcode: Fix crashes on early 486 CPUs due to usage of 'cpuid'.

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Message-ID: <20250405210312.GDZ_GakEONiwRpIU6T@fat_crate.local>
Date: Sat, 5 Apr 2025 23:03:12 +0200
From: Borislav Petkov <bp@...en8.de>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: Kevin Koster <lkml@...ertech.com>, Oerg866 <oerg866@...glemail.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org
Subject: Re: [PATCH] x86/microcode: Fix crashes on early 486 CPUs due to
 usage of 'cpuid'.

On Sat, Apr 05, 2025 at 10:50:13PM +0200, Borislav Petkov wrote:
> On Sat, Apr 05, 2025 at 01:33:46PM -0700, H. Peter Anvin wrote:
> > How the Hades does c->x86 not get set to 4 (hence < 0x10) on this CPU?
> > 
> > That's the real bug imo...
> 
> Go to the first mail in the thread.
> 
> 4c585af7180c ("x86/boot/32: Temporarily map initrd for microcode loading")
> 
> walks straight into  native_cpuid_ecx().

... and what you're *really* asking is why that dis_ucode_ldr is there in
save_microcode_in_initrd() - because tglx made it an early_initcall() so it
runs independently of the loader detection logic and thus needs this check.

So I figure I'll stick all the checking logic into a single function which
everything can call now...

-- 
Regards/Gruss,
    Boris.

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