linux-kernel - Re: [PATCH] x86: correct fpu emulation access to ldt

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Message-ID: <55C1D33F.20803@suse.com>
Date:	Wed, 5 Aug 2015 11:11:27 +0200
From:	Juergen Gross <jgross@...e.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	billm@...bpc.org.au,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: correct fpu emulation access to ldt

On 08/04/2015 08:01 PM, Andy Lutomirski wrote:
> On Tue, Aug 4, 2015 at 8:02 AM, Juergen Gross <jgross@...e.com> wrote:
>> Commit 14805442532c ("x86/ldt: Make modify_ldt synchronous") introduced
>> a new struct ldt_struct anchored at mm->context.ldt.
>>
>> Adapt the x86 fpu emulation to use that new structure.
>>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
>
> Whoops!
>
> Does this need to Cc: stable?

Probably.

> Also, want to make it slightly fancier so we can drop the dependency
> on CONFIG_MODIFY_LDT_SYSCALL?

Something like:

-#define LDT_DESCRIPTOR(s) (((struct desc_struct 
*)current->mm->context.ldt)[(s) >> 3])
+#ifdef CONFIG_MODIFY_LDT_SYSCALL
+#define LDT_DESCRIPTOR(s) (current->mm->context.ldt->entries[(s) >> 3])
+#else
+#define LDT_DESCRIPTOR(s) ((struct desc_struct){{{ .a = 0, .b = 0, }}})
+#endif

I'd need to specify the corresponding patch as a prerequisite for stable
I guess? How to do this before it is picked by Linus?


Juergen
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