linux-kernel - Re: [PATCH 1/2] uprobes: add comment with insn opcodes, mnemonics and why we dont support them

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Message-ID: <5369156C.4000602@redhat.com>
Date:	Tue, 06 May 2014 19:01:32 +0200
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	linux-kernel@...r.kernel.org, Jim Keniston <jkenisto@...ibm.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 1/2] uprobes: add comment with insn opcodes, mnemonics
 and why we dont support them

On 05/05/2014 09:41 PM, Oleg Nesterov wrote:
> On 05/05, Denys Vlasenko wrote:
>>
>> + * Opcodes we'll probably never support:
>> + * 6c-6f - ins,outs. SEGVs if used in userspace
>> + * e4-e7 - in,out imm. SEGVs if used in userspace
>> + * ec-ef - in,out acc. SEGVs if used in userspace
> 
> Well. I have no idea why they are nacked, but this is not the reason.
> 
> SEGVs are fine. Plus we have ioperm().

Noted.

Oleg, can you clear for me the following -

If the probed instruction triggers an "illegal insn" or "privileged insn"
CPU exception - are we completely fine?

Or there are some problems? how bad are they?
Slightly wrong signal stack? Wrong EFLAGs on stack?
Wrong address of failing insn?
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