linux-kernel - Re: [RFC 6/8] ARM64: Handle TRAP

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Message-ID: <20150102180523.GC6761@redhat.com>
Date:	Fri, 2 Jan 2015 19:05:23 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Pratyush Anand <panand@...hat.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux@....linux.org.uk,
	tixy@...aro.org, ananth@...ibm.com, sandeepa.prabhu@...aro.org,
	catalin.marinas@....com, will.deacon@....com,
	linux-kernel@...r.kernel.org, anil.s.keshavamurthy@...el.com,
	masami.hiramatsu.pt@...achi.com, wcohen@...hat.com
Subject: Re: [RFC 6/8] ARM64: Handle TRAP_HWBRKPT for user mode as well

Let me repeat once again that I know absolutely nothing about arm* ;)

On 12/31, Pratyush Anand wrote:
>
> uprobe registers a handler at step_hook. So, single_step_handler now
> checks for user mode as well if there is a valid hook.
>
> Signed-off-by: Pratyush Anand <panand@...hat.com>
> ---
>  arch/arm64/kernel/debug-monitors.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
> index b056369fd47d..2676b8655241 100644
> --- a/arch/arm64/kernel/debug-monitors.c
> +++ b/arch/arm64/kernel/debug-monitors.c
> @@ -236,6 +236,9 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
>  	if (!reinstall_suspended_bps(regs))
>  		return 0;
>
> +	if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
> +		return 0;
> +
>  	if (user_mode(regs)) {
>  		info.si_signo = SIGTRAP;
>  		info.si_errno = 0;
> @@ -251,9 +254,6 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
>  		 */
>  		user_rewind_single_step(current);
>  	} else {
> -		if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
> -			return 0;
> -

Agreed, we need something like this change...

But did you verify that it can't break other users of register_step_hook() ?
The current handlers do not check user_mode() == F, they assume that they
can't be called otherwise.

If this all is correct, please explain why in the changelog.

The same for the next patch.

Oleg.

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