linux-kernel - RE: [PATCH] x86/i8259: Work around buggy legacy PIC

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <bbf5d417ee0d4edbbed31f19ef40fad0@AcuMS.aculab.com>
Date:   Fri, 14 May 2021 13:13:19 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Thomas Gleixner' <tglx@...utronix.de>,
        'Maximilian Luz' <luzmaximilian@...il.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>
CC:     "H. Peter Anvin" <hpa@...or.com>, Sachi King <nakato@...ato.io>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH] x86/i8259: Work around buggy legacy PIC

From: Thomas Gleixner
> Sent: 14 May 2021 14:02
> 
> David,
> 
> On Thu, May 13 2021 at 10:36, David Laight wrote:
> 
> >> -----Original Message-----
> >> From: Maximilian Luz <luzmaximilian@...il.com>
> 
> can you please fix your mail client and spare us the useless header
> duplication in the reply?

I have to delete them by hand - must have forgotten, I can't fix outlook :-)

> > It is also worth noting that the probe code is spectacularly crap.
> > It writes 0xff and then checks that 0xff is read back.
> > Almost anything (including a failed PCIe read to the ISA bridge)
> > will return 0xff and make the test pass.
> 
>         unsigned char probe_val = ~(1 << PIC_CASCADE_IR);
> 
> 	outb(probe_val, PIC_MASTER_IMR);
> 	new_val = inb(PIC_MASTER_IMR);
> 
> How is that writing 0xFF?

Sorry I misread the code and diagnostic output.

In any case writing a value and expecting the same value back
isn't exactly a high-quality probe.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)