linux-kernel - Re: Q: user_enable_single_step() && update

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20120801150119.GA8845@redhat.com>
Date:	Wed, 1 Aug 2012 17:01:19 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Roland McGrath <roland@...k.frob.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	ananth@...ibm.com, a.p.zijlstra@...llo.nl, mingo@...hat.com,
	srikar@...ux.vnet.ibm.com
Subject: Re: Q: user_enable_single_step() && update_debugctlmsr()

On 08/01, Sebastian Andrzej Siewior wrote:
>
> So a patch like
> --- a/arch/x86/kernel/step.c
> +++ b/arch/x86/kernel/step.c
> @@ -173,8 +173,8 @@ static void enable_step(struct task_struct *child,  
> bool block)
>                 unsigned long debugctl = get_debugctlmsr();
>
>                 debugctl |= DEBUGCTLMSR_BTF;
> -               update_debugctlmsr(debugctl);
>                 set_tsk_thread_flag(child, TIF_BLOCKSTEP);
> +               update_debugctlmsr(debugctl);
>         } else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) {
>                 unsigned long debugctl = get_debugctlmsr();
>
> should fix the race

No, I don't think it can fix something ;) or make any difference.

> and _yes_ I also would follow your suggestion to
> remove this update_debugctlmsr() here since switch_to() should do this.

Agreed, but once again, uprobes needs it if child == current (but we should
move this code into the trivial helper). If we change (I hope) uprobes to
avoid user_enable_single_step() we will export the helper.

Oleg.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/