linux-kernel - Re: [PATCH 12/X] uprobes: x86: introduce abort

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Date:	Fri, 21 Oct 2011 20:12:07 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 12/X] uprobes: x86: introduce abort_xol()

Hey Oleg,

> A separate "patch", just to emphasize that I do not know what
> actually abort_xol() should do! I do not understand this asm
> magic.
> 
> This patch simply changes regs->ip back to the probed insn,
> obviously this is not enough to handle UPROBES_FIX_*. Please
> take care.
> 
> If it is not clear, abort_xol() is needed when we should
> re-execute the original insn (replaced with int3), see the
> next patch.

We should be removing the breakpoint in abort_xol().
Otherwise if we just set the instruction pointer to int3 and signal a
sigill, then the user may be confused why a breakpoint is generating
SIGILL.

> ---
>  arch/x86/include/asm/uprobes.h |    1 +
>  arch/x86/kernel/uprobes.c      |    9 +++++++++
>  2 files changed, 10 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
> index f0fbdab..6209da1 100644
> --- a/arch/x86/include/asm/uprobes.h
> +++ b/arch/x86/include/asm/uprobes.h
> @@ -51,6 +51,7 @@ extern void set_instruction_pointer(struct pt_regs *regs, unsigned long vaddr);
>  extern int pre_xol(struct uprobe *uprobe, struct pt_regs *regs);
>  extern int post_xol(struct uprobe *uprobe, struct pt_regs *regs);
>  extern bool xol_was_trapped(struct task_struct *tsk);
> +extern void abort_xol(struct pt_regs *regs);
>  extern int uprobe_exception_notify(struct notifier_block *self,
>  				       unsigned long val, void *data);
>  #endif	/* _ASM_UPROBES_H */
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index c861c27..bc11a89 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -511,6 +511,15 @@ bool xol_was_trapped(struct task_struct *tsk)
>  	return false;
>  }
> 
> +void abort_xol(struct pt_regs *regs)
> +{
> +	// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
> +	// !!! Dear Srikar and Ananth, please implement me !!!
> +	// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
> +	struct uprobe_task *utask = current->utask;
> +	regs->ip = utask->vaddr;

nit:
Shouldnt we be setting the ip to the next instruction after this
instruction?

> +}
> +
>  /*
>   * Called after single-stepping. To avoid the SMP problems that can
>   * occur when we temporarily put back the original opcode to


I have applied all your patches and ran tests, the tests are all
passing.

I will fold them into my patches and send them out.

-- 
Thanks and Regards
Srikar

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