linux-kernel - Re: [crash, bisected] Re: [PATCH 3/4] x86

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: <m1skv7onvh.fsf@frodo.ebiederm.org>
Date:	Fri, 20 Jun 2008 13:25:06 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Mike Travis <travis@....com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Christoph Lameter <clameter@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu area

Mike Travis <travis@....com> writes:

> Jeremy Fitzhardinge wrote:
>>
>> 
>> BTW, I think __per_cpu_load will cause trouble if you make a relocatable
>> kernel, being an absolute symbol.  But I have relocation off at the moment.
>> 
> ...
> Here's where it's defined (in include/asm-generic/vmlinux.lds.h):
>
> #ifdef CONFIG_HAVE_ZERO_BASED_PER_CPU
> #define PERCPU(align)                                                   \
>         . = ALIGN(align);                                               \
>         percpu : { } :percpu                                            \
>         __per_cpu_load = .;                                             \
>         .data.percpu 0 : AT(__per_cpu_load - LOAD_OFFSET) {             \
>                 *(.data.percpu.first)                                   \
>                 *(.data.percpu.shared_aligned)                          \
>                 *(.data.percpu)                                         \
>                 *(.data.percpu.page_aligned)                            \
>                 ____per_cpu_size = .;                                   \
>         }                                                               \
>         . = __per_cpu_load + ____per_cpu_size;                          \
>         data : { } :data
> #else
>
> Can we generate a new symbol which would account for LOAD_OFFSET?

Ouch.  Absolute symbols indeed.  On the 32bit kernel that may play havoc
with the relocatable kernel, although we have had similar absolute logic
for the last year. With __per_cpu_start and __per_cpu_end so it may
not be a problem.

To initialize the percpu data you do want to talk to the virtual address
at __per_coup_load.  But it is absolute Ugh.  

It might be worth saying something like.
.data.percpu.start : AT(.data.percpu.dummy - LOAD_OFFSET) {
	DATA(0)                   
	. = ALIGN(align);
        __per_cpu_load = . ;                   
}
To make __per_cpu_load a relative symbol. ld has a bad habit of taking
symbols out of empty sections and making them absolute.  Which is why
I added the DATA(0).

Still I don't think that would be the 64bit problem.

Eric

--
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/