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From: "H. Peter Anvin" <hpa@zytor.com>
To: linux-kernel@vger.kernel.org, luto@amacapital.net,
	torvalds@linux-foundation.org, mingo@kernel.org,
	tglx@linutronix.de, linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/urgent] x86/tls: Don't validate lm in set_thread_area() after all
Date: Thu, 18 Dec 2014 08:59:28 -0800	[thread overview]
Message-ID: <549307F0.7090009@zytor.com> (raw)
In-Reply-To: <tip-3fb2f4237bb452eb4e98f6a5dbd5a445b4fed9d0@git.kernel.org>

On 12/18/2014 03:16 AM, tip-bot for Andy Lutomirski wrote:
> Commit-ID:  3fb2f4237bb452eb4e98f6a5dbd5a445b4fed9d0
> Gitweb:     http://git.kernel.org/tip/3fb2f4237bb452eb4e98f6a5dbd5a445b4fed9d0
> Author:     Andy Lutomirski <luto@amacapital.net>
> AuthorDate: Wed, 17 Dec 2014 14:48:30 -0800
> Committer:  Ingo Molnar <mingo@kernel.org>
> CommitDate: Thu, 18 Dec 2014 12:12:26 +0100
> 
> x86/tls: Don't validate lm in set_thread_area() after all
> 
> It turns out that there's a lurking ABI issue.  GCC, when
> compiling this in a 32-bit program:
> 
> struct user_desc desc = {
> 	.entry_number    = idx,
> 	.base_addr       = base,
> 	.limit           = 0xfffff,
> 	.seg_32bit       = 1,
> 	.contents        = 0, /* Data, grow-up */
> 	.read_exec_only  = 0,
> 	.limit_in_pages  = 1,
> 	.seg_not_present = 0,
> 	.useable         = 0,
> };
> 
> will leave .lm uninitialized.  This means that anything in the
> kernel that reads user_desc.lm for 32-bit tasks is unreliable.
> 

No, it won't.  However, if you initialize this dynamically field by
field rather than as an initializer, then you are correct.

	-hpa


  reply	other threads:[~2014-12-18 16:59 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-12-17 22:48 [PATCH resend] x86, tls: Don't validate lm in set_thread_area " Andy Lutomirski
2014-12-18 11:16 ` [tip:x86/urgent] x86/tls: Don't validate lm in set_thread_area() " tip-bot for Andy Lutomirski
2014-12-18 16:59   ` H. Peter Anvin [this message]
2014-12-18 18:26     ` Andy Lutomirski
2014-12-18 19:03     ` Linus Torvalds

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