linux-kernel - Re: [patch] i386: remove IOPL check on task switch

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: <454B850C.3050402@vmware.com>
Date:	Fri, 03 Nov 2006 10:06:04 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Chuck Ebbert <76306.1226@...puserve.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>, Andi Kleen <ak@...e.de>
Subject: Re: [patch] i386: remove IOPL check on task switch

Chuck Ebbert wrote:
> IOPL is implicitly saved and restored on task switch,
> so explicit check is no longer needed.
>
> Signed-off-by: Chuck Ebbert <76306.1226@...puserve.com>
>
> --- 2.6.19-rc4-32smp.orig/arch/i386/kernel/process.c
> +++ 2.6.19-rc4-32smp/arch/i386/kernel/process.c
> @@ -681,12 +681,6 @@ struct task_struct fastcall * __switch_t
>  		loadsegment(gs, next->gs);
>  
>  	/*
> -	 * Restore IOPL if needed.
> -	 */
> -	if (unlikely(prev->iopl != next->iopl))
> -		set_iopl_mask(next->iopl);
> -
> -	/*
>  	 * Now maybe handle debug registers and/or IO bitmaps
>  	 */
>  	if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW)
>   

Nack.  This is used for paravirt-ops kernels that use IOPL'd userspace.  
Fixing it would require a fairly heavy penalty on the iret path, since 
every single instruction there contributes to a critical region which 
must have custom fixup code, or some other technique to provide 
protection against interrupt re-entrancy.

At least, let's discuss other potential solutions first - for now it is 
harmless.

Zach
-
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/