linux-kernel - Re: [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF

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Message-ID: <a2937a74-c63c-527d-da26-eb4dd10468a4@virtuozzo.com>
Date:	Fri, 3 Jun 2016 13:27:33 +0300
From:	Dmitry Safonov <dsafonov@...tuozzo.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
CC:	<linux-kernel@...r.kernel.org>, <mingo@...hat.com>,
	<luto@...capital.net>, <tglx@...utronix.de>, <hpa@...or.com>,
	<x86@...nel.org>, <0x7f454c46@...il.com>, <oleg@...hat.com>,
	<xemul@...tuozzo.com>, <khorenko@...tuozzo.com>,
	Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF_IA32)

On 06/03/2016 12:57 PM, Cyrill Gorcunov wrote:
> On Wed, Jun 01, 2016 at 04:11:36PM +0300, Dmitry Safonov wrote:
>> As the task isn't executing at the moment of {GET,SET}REGS,
>> return regset that corresponds to code selector, rather than
>> value of TIF_IA32 flag.
>> I.e. if we ptrace i386 elf binary that has just changed it's
>> code selector to __USER_CS, than GET_REGS will return
>> full x86_64 register set.
>>
>> Note, that this will work only if application has changed it's CS.
>> If the application does 32-bit syscall with __USER_CS, ptrace
>> will still return 64-bit register set. Which might be still confusing
>> for tools that expect TS_COMPACT to be exposed [1, 2].
>>
>> So this this change should make PTRACE_GETREGSET more reliable and
>> this will be another step to drop TIF_{IA32,X32} flags.
>>
>> [1]: https://sourceforge.net/p/strace/mailman/message/30471411/
>> [2]: https://lkml.org/lkml/2012/1/18/320
>>
>> Cc: Andy Lutomirski <luto@...nel.org>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: "H. Peter Anvin" <hpa@...or.com>
>> Cc: Oleg Nesterov <oleg@...hat.com>
>> Signed-off-by: Dmitry Safonov <dsafonov@...tuozzo.com>
>
> Looks reasonable! Still if cs has been changed to non-compat
> selector and we now return 64bit registers set, won't it
> cause problems for old tools? I suspect it should not but
> still.
>

Thanks! Hmm, strace works fine - I'll check gdb to be sure.
What else could be bothered by this?