linux-kernel - Re: [PATCH 4/5] x86-64: Replace vsyscall gettimeofday fallback with int 0xcc

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Message-ID: <BANLkTikHQ8+44K8f3tB87XmroX=EQYAS6g@mail.gmail.com>
Date:	Sun, 29 May 2011 16:04:36 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] x86-64: Replace vsyscall gettimeofday fallback with
 int 0xcc

On Sun, May 29, 2011 at 4:01 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Andrew Lutomirski <luto@....edu> wrote:
>
>> On Sun, May 29, 2011 at 3:49 PM, Ingo Molnar <mingo@...e.hu> wrote:
>> >
>> > * Andrew Lutomirski <luto@....edu> wrote:
>> >
>> >> > Ok, i suspect you marked it 0xCC because that's the INT3 instruction
>> >> > - not very useful for exploits?
>> >>
>> >> Exactly.
>> >>
>> >> The comments in irq_vectors.h make it sound like vectors 0x81..0xed
>> >> are used for device interrupts but AFAICT it's only 0x20..0x39 that
>> >> are used, so the precise choice of vector doesn't matter that much.
>> >
>> > No, we use almost all of the vector space for device interrupts. Why
>> > do you think only 0x20..0x39 is used?
>>
>> Possibility my inability to understand all the IRQ mapping code in
>> just half an hour of trying.
>
> Hey, you managed to find all the scattered pieces in just half an
> hour, i'm impressed ;-)

grep and an SSD are amazing.  I'll add the BUG_ON just to satisfy my
paranoia.  I'll also update the comment in irq_vectors.h.

--Andy
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