linux-kernel - Re: [PATCH] x86 : Ensure X86_FLAGS

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: <alpine.DEB.2.02.1409292059530.22082@ionos.tec.linutronix.de>
Date:	Mon, 29 Sep 2014 21:33:58 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Sebastian Lackner <sebastian@...-team.de>
cc:	Andy Lutomirski <luto@...capital.net>,
	Anish Bhatt <anish@...lsio.com>, linux-kernel@...r.kernel.org,
	x86@...nel.org, mingo@...hat.com, hpa@...or.com
Subject: Re: [PATCH] x86 : Ensure X86_FLAGS_NT is cleared on syscall entry

On Mon, 29 Sep 2014, Sebastian Lackner wrote:
> On 29.09.2014 19:40, Andy Lutomirski wrote:
> Well, the best documentation I've found is something like
> http://www.fermimn.gov.it/linux/quarta/x86/int.htm
> 
> which states:
> 
> --- snip ---
> INTERRUPT-TO-INNER-PRIVILEGE:
>    [...]
>    TF := 0;
>    NT := 0;
> --- snip ---
> (Doesn't say anything about HW interrupts though)
> 
> This also makes sense at my opinion, since the interrupt handler has
> to know if it should return to the previous task (when NT=1) or to
> the same task (when NT=0).

No, it does not. Simply because Linux does not support nested tasks at
all, because the TSS is not accessible and the TSS.back_link is
sturdily NULL. So even if it would not explode with a #GP in IA-32e
mode it would explode while trying to execute the instruction at NULL.

> That might be possible. It probably makes sense to review other
> parts of the code, for similar issues.

What's the issue? Stupid user space programs segfaulting?

Thanks,

	tglx
--
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/