Re: [PATCH] x86: use enum instead of literals for trap values

[Kees Cook]

On Fri, Mar 9, 2012 at 11:08 AM, Borislav Petkov <bp@xxxxxxxxx> wrote:
> On Fri, Mar 09, 2012 at 10:54:19AM -0800, Kees Cook wrote:
>> On Fri, Mar 9, 2012 at 10:28 AM, Borislav Petkov <bp@xxxxxxxxx> wrote:
>> > On Fri, Mar 09, 2012 at 10:21:52AM -0800, Kees Cook wrote:
>> >> > I have to admit personally to prefer something like X86_XCP_XX where XX
>> >> > is the two-letter code that the Intel documentation uses for that trap,
>> >> > i.e. #GP, #BR, #MC and so on.
>> >>
>> >> We need a single person to decide on this bike shed color. :) If the
>> >> list of enum names can be agreed on, I'll be happy to do the
>> >> search/replace for it.
>> >
>> > Well,
>> >
>> > here are my 2¢: I agree with hpa because
>> >
>> > a) it maps the CPU vendor documentation
>> > b) it is nicely short
>>
>> How about:
>>
>> X86_XCP_DE = 0,         /* 0, Divide-by-zero */
>> X86_XCP_DB,             /* 1, Debug */
>> X86_XCP_NMI,            /* 2, Non-maskable Interrupt */
>> X86_XCP_BP,             /* 3, Breakpoint */
>> X86_XCP_OF,             /* 4, Overflow */
>> X86_XCP_BR,             /* 5, Bound Range Exceeded */
>> X86_XCP_UD,             /* 6, Invalid Opcode */
>> X86_XCP_NM,             /* 7, Device Not Available */
>> X86_XCP_DF,             /* 8, Double Fault */
>> X86_XCP_OLD_MF,         /* 9, Coprocessor Segment Overrun */
>> X86_XCP_TS,             /* 10, Invalid TSS */
>> X86_XCP_NP,             /* 11, Segment Not Present */
>> X86_XCP_SS,             /* 12, Stack-Segment Fault */
>> X86_XCP_GP,             /* 13, General Protection Fault  */
>> X86_XCP_PF,             /* 14, Page Fault */
>> X86_XCP_RES,            /* 15, Reserved */
>
> So is this reserved or are we using it for Spurious IRQs? If we use it,
> then 'RES' is a bad name. Maybe we define our own like
>
> X86_VEC_SP

Yeah, it's used for spurious.

> and then do
>
> X86_VEC_IR for IRET
>
> in the manner we assumed for the rest?

Sure. I wasn't sure if it was dangerous to take a two-letter combo. I
guess if there is a future collision, we can just solve it then.

>> X86_XCP_MF,             /* 16, x87 Floating-Point Exception */
>> X86_XCP_AC,             /* 17, Alignment Check */
>> X86_XCP_MC,             /* 18, Machine Check */
>> X86_XCP_XM,             /* 19, SIMD Floating-Point Exception */
>
> Shouln't this be #XF actually? At least it is so in the AMD docs.

XM in Intel, XF in AMD. I have no preference.

>> X86_XCP_IRET = 32,      /* 32, IRET Exception */
>>
>> There is a name collision for "MF", there's no mnemonic for NMI,
>
> Well, in the AMD docs we actually do have the '#NMI' mnemonic in use.

If AMD's list is more complete, I think that's a good enough reason to
use "XF" above. :)

>> IRET, or the reserved "spurious" interrupt.
>>
>> Can use "VEC" instead "XCP", as Steven suggests.
>
> Yeah, because those actually are fixed interrupt vectors, as they're
> called in the AMD docs. Makes sense.

That seems reasonable to me. Peter, how's that sound to you?

-Kees

-- 
Kees Cook
ChromeOS Security
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