linux-kernel - Re: [PATCH 1/2] x86: Ignore trap bits on single step exceptions

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: <4CED7642.8070600@redhat.com>
Date:	Wed, 24 Nov 2010 21:32:02 +0100
From:	Michael Stefaniuc <mstefani@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Maciej Rutecki <maciej.rutecki@...il.com>,
	Alexandre Julliard <julliard@...ehq.org>,
	Jason Wessel <jason.wessel@...driver.com>,
	"All since 2.6.33.x" <stable@...nel.org>
Subject: Re: [PATCH 1/2] x86: Ignore trap bits on single step exceptions

Hello Frederic,

On 11/13/2010 10:37 PM, Frederic Weisbecker wrote:
> When a single step exception fires, the trap bits, used to
> signal hardware breakpoints, are in a random state.
>
> These trap bits might be set if another exception will follow,
> like a breakpoint in the next instruction, or a watchpoint in the
> previous one. Or there can be any junk there.
>
> So if we handle these trap bits during the single step exception,
> we are going to handle an exception twice, or we are going to
> handle junk.
>
> Just ignore them in this case.
>
> This fixes https://bugzilla.kernel.org/show_bug.cgi?id=21332
sorry for the delay in testing this.

I have cherry-picked this patch on top of v2.6.37-rc3-102-gea49b16 and 
the ntdll/exception tests pass now.

Many thanks
bye
	michael

>
> Reported-by: Michael Stefaniuc<mstefani@...hat.com>
> Signed-off-by: Frederic Weisbecker<fweisbec@...il.com>
> Cc: Rafael J. Wysocki<rjw@...k.pl>
> Cc: Maciej Rutecki<maciej.rutecki@...il.com>
> Cc: Alexandre Julliard<julliard@...ehq.org>
> Cc: Jason Wessel<jason.wessel@...driver.com>
> Cc: All since 2.6.33.x<stable@...nel.org>
> ---
>   arch/x86/kernel/hw_breakpoint.c |    4 ++++
>   1 files changed, 4 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
> index ff15c9d..42c5942 100644
> --- a/arch/x86/kernel/hw_breakpoint.c
> +++ b/arch/x86/kernel/hw_breakpoint.c
> @@ -433,6 +433,10 @@ static int __kprobes hw_breakpoint_handler(struct die_args *args)
>   	dr6_p = (unsigned long *)ERR_PTR(args->err);
>   	dr6 = *dr6_p;
>
> +	/* If it's a single step, TRAP bits are random */
> +	if (dr6&  DR_STEP)
> +		return NOTIFY_DONE;
> +
>   	/* Do an early return if no trap bits are set in DR6 */
>   	if ((dr6&  DR_TRAP_BITS) == 0)
>   		return NOTIFY_DONE;


-- 
Michael Stefaniuc                           Tel.: +49-711-96437-199
Consulting Communications Engineer          Fax.: +49-711-96437-111
--------------------------------------------------------------------
Reg. Adresse: Red Hat GmbH, Otto-Hahn-Strasse 20, 85609 Dornach
Handelsregister: Amtsgericht Muenchen HRB 153243
Geschäftsführer: Brendan Lane, Charlie Peters, Michael Cunningham,
                  Charles Cachera
--
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/