linux-kernel - Re: PTRACE_SYSCALL && vsyscall (Was: arch_check_bp_in

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Date:	Wed, 5 Dec 2012 10:29:51 +0100
From:	Jan Kratochvil <jan.kratochvil@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>, mosix@...ix.com.au
Cc:	Amnon Shiloh <u3557@...o.sublimeip.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Pedro Alves <palves@...hat.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org
Subject: Re: PTRACE_SYSCALL && vsyscall (Was: arch_check_bp_in_kernelspace:
 fix the range check)

On Sun, 02 Dec 2012 20:30:58 +0100, Oleg Nesterov wrote:
> Yes, that is why I said this needs the new option.

I do not mind new options although personally I do not find them meaningful
for an already deprecated ABI compatibility-only issue.


> If the tracer does PTRACE_SYSCALL the tracee reports syscall exit
> _after_ gettimeofday/etc. The tracer can look at regs->orig_ax == -1
> and detect that this is not syscall but vsyscall, it can look at
> regs->ip then (not with the patch below).

I believe applications just call PTRACE_SYSCALL twice, without checking
orig_eax.  At least strace and its TCB_INSYSCALL looks so.


On Mon, 03 Dec 2012 00:54:58 +0100, u3557@...o.sublimeip.com wrote:
> The beauty of using the x86 debug-registers,

x86 debug registers are already very scarce.  Besides that userland
applications know they have 4 of them available so it would also break them.


Regards,
Jan
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