linux-kernel - Re: [PATCH v3 2/7] x86/arch_prctl: Fix ARCH_GET_FS and ARCH_GET

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Message-ID: <20160408071354.GB22579@gmail.com>
Date:	Fri, 8 Apr 2016 09:13:54 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	Borislav Petkov <bp@...en8.de>, security@...nel.org,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rudolf Marek <r.marek@...embler.cz>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v3 2/7] x86/arch_prctl: Fix ARCH_GET_FS and ARCH_GET_GS


* Andy Lutomirski <luto@...nel.org> wrote:

> ARCH_GET_FS and ARCH_GET_GS attempted to figure out the fsbase and
> gsbase respectively from saved thread state.  This was wrong: fsbase
> and gsbase live in registers while a thread is running, not in
> memory.

So I'm wondering, the current code looks totally broken,what user-space code can 
possibly use this? I checked glibc and Wine, and neither of them does. Wine uses 
ARCH_SET_GS and glibc uses ARCH_SET_FS, but that's all - neither actually tries to 
use the ARCH_GET_* reading APIs.

So for backporting purposes I'd be much happier about simply returning -EINVAL or 
-ENOSYS, and we could re-introduce this code in v4.7.

Thanks,

	Ingo