linux-kernel - Re: [PATCH] x86: introduce push/pop macros which generate CFI_REL_OFFSET and CFI

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Date:	Mon, 12 Jan 2015 12:22:10 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...en8.de>
CC:	Denys Vlasenko <dvlasenk@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	X86 ML <x86@...nel.org>, Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] x86: introduce push/pop macros which generate CFI_REL_OFFSET
 and CFI_RESTORE

On 01/12/2015 12:14 PM, Andy Lutomirski wrote:
> On Mon, Jan 12, 2015 at 12:11 PM, Borislav Petkov <bp@...en8.de> wrote:
>> On Mon, Jan 12, 2015 at 11:46:53AM -0800, Andy Lutomirski wrote:
>>> Dumb example:
>>>
>>>     pushq_cfi $__KERNEL_DS /* ss */
>>>
>>> This doesn't save anything that the unwinder would care about.
>>
>> And? The unwinder or whatever looks at that info simply ignores stuff it
>> is not interested in, no?
> 
> But CFI_REL_OFFSET $__KERNEL_DS, 0 probably isn't even well-formed and
> won't build.
> 

I think this is relatively easy to deal with at the expense of a large
.ifeq statement in the macro.

	-hpa


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