linux-kernel - Re: [PATCH 4/5] arm64: Handle TRAP

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Message-ID: <20160906163434.GH19605@e104818-lin.cambridge.arm.com>
Date:   Tue, 6 Sep 2016 17:34:34 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Pratyush Anand <panand@...hat.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux@....linux.org.uk,
        will.deacon@....com, Yang Shi <yang.shi@...aro.org>,
        steve.capper@...aro.org, srikar@...ux.vnet.ibm.com,
        Suzuki K Poulose <suzuki.poulose@....com>,
        vijaya.kumar@...iumnetworks.com, linux-kernel@...r.kernel.org,
        oleg@...hat.com, dave.long@...aro.org,
        Sandeepa Prabhu <sandeepa.s.prabhu@...il.com>,
        wcohen@...hat.com
Subject: Re: [PATCH 4/5] arm64: Handle TRAP_BRKPT for user mode as well

On Tue, Aug 02, 2016 at 11:00:08AM +0530, Pratyush Anand wrote:
> --- a/arch/arm64/kernel/debug-monitors.c
> +++ b/arch/arm64/kernel/debug-monitors.c
> @@ -326,16 +326,20 @@ NOKPROBE_SYMBOL(call_break_hook);
>  static int brk_handler(unsigned long addr, unsigned int esr,
>  		       struct pt_regs *regs)
>  {
> -	if (user_mode(regs)) {
> -		send_user_sigtrap(TRAP_BRKPT);
> -	}
> +	bool handler_found = false;
> +
>  #ifdef	CONFIG_KPROBES
> -	else if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) {
> -		if (kprobe_breakpoint_handler(regs, esr) != DBG_HOOK_HANDLED)
> -			return -EFAULT;
> +	if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) {
> +		if (kprobe_breakpoint_handler(regs, esr) == DBG_HOOK_HANDLED)
> +			handler_found = true;
>  	}
>  #endif
> -	else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
> +	if (!handler_found && call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
> +		handler_found = true;
> +
> +	if (!handler_found && user_mode(regs)) {
> +		send_user_sigtrap(TRAP_BRKPT);
> +	} else if (!handler_found) {
>  		pr_warn("Unexpected kernel BRK exception at EL1\n");
>  		return -EFAULT;
>  	}

I think we could do the same here with a single call_break_hook() and
making sure that the corresponding handlers check the esr for the
corresponding BRK encoding.

-- 
Catalin