linux-kernel - Re: [tip:x86/urgent] x86/apic: Fix signedness bug in APIC ID validity checks

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Date:   Wed, 11 Apr 2018 22:21:37 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dou Liyang <douly.fnst@...fujitsu.com>
cc:     peterz@...radead.org, lirongqing@...du.com,
        linux-kernel@...r.kernel.org, mingo@...nel.org, hpa@...or.com,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/urgent] x86/apic: Fix signedness bug in APIC ID validity
 checks

On Wed, 11 Apr 2018, Dou Liyang wrote:

> Hi Thomas,
> 
> At 04/10/2018 10:51 PM, tip-bot for Li RongQing wrote:
> [...]
> 
> > x86/apic: Fix signedness bug in APIC ID validity checks
> > 
> > The APIC ID as parsed from ACPI MADT is validity checked with the
> > apic->apic_id_valid() callback, which depends on the selected APIC type.
> > 
> > For non X2APIC types APIC IDs >= 0xFF are invalid, but values > 0x7FFFFFFF
> 
> Today when I am reading "Intel® 64 Architecture x2APIC Specification", I
> find that below in chapter 2.4.1:
> 
>   The APIC ID value of FFFF_FFFFH and the highest value corresponding to
>   the imple-mented bit-width of the local APIC ID register in the system
>   are reserved and cannot be assigned to any logical processor.
> 
> Seems, FFFF_FFFFH is also invalid for X2APIC types, Shall we also do the
> validity check for X2APIC ID?
> 
> acpi_parse_x2apic()
> 	...
> 	/* Ignore invalid ID */
> 	if (apic_id == 0xffffffff)
> 		return 0;

Yes. I noticed that as well and just did not come around to write the
patch.

Thanks,

	tglx