* correction to compat_sys_kexec_load
@ 2008-05-23 11:36 Sharyathi Nagesh
2008-05-23 20:14 ` Eric W. Biederman
0 siblings, 1 reply; 6+ messages in thread
From: Sharyathi Nagesh @ 2008-05-23 11:36 UTC (permalink / raw)
To: linux-kernel, fastboot, akpm, maneesh, ebiederm, mohan, sachinp
Cc: mohd.omar, IndhuDurai
[-- Attachment #1: Type: text/plain, Size: 972 bytes --]
Hi
While testing with kexec tool, I observed some problems. When
application (kexec) is 32 bit and kernel is 64 bit I observed that
loading crash kernel works without any issues but unloading crash kernel
fails.
--------------------------------------------------------
running strace over 'kexec -u -p'
show the problem to be with sys_kexec_load() call
sys_kexec_load(0, 0, 0, 0x1, 0) = -1 EINVAL (Invalid argument)
write(2, "kexec_load (0 segments) failed: "..., 49
kexec_load (0 segments) failed: Invalid argument
) = 4
--------------------------------------------------------
This is patch to fix the problem, I think kernel code had a typo where in:
if((flags & KEXEC_ARCH_MASK) == KEXEC_ARCH) was used instead of
if((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH)
This patch takes care of that, I have tested the patch it worked fine
for me. Please review the patch and let me know of your views. This
patch is based on linux-2.6.26-rc3.
Thanks
Yeehaw
[-- Attachment #2: compat_sys_kexec_correction.patch --]
[-- Type: text/x-patch, Size: 596 bytes --]
Index: linux-2.6.25.3-2/kernel/kexec.c
===================================================================
--- linux-2.6.25.3-2.orig/kernel/kexec.c 2008-05-23 14:57:08.000000000 +0530
+++ linux-2.6.25.3-2/kernel/kexec.c 2008-05-23 15:00:41.000000000 +0530
@@ -1068,7 +1068,8 @@
/* Don't allow clients that don't understand the native
* architecture to do anything.
*/
- if ((flags & KEXEC_ARCH_MASK) == KEXEC_ARCH_DEFAULT)
+ if (((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH) &&
+ ((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH_DEFAULT))
return -EINVAL;
if (nr_segments > KEXEC_SEGMENT_MAX)
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: correction to compat_sys_kexec_load
2008-05-23 11:36 correction to compat_sys_kexec_load Sharyathi Nagesh
@ 2008-05-23 20:14 ` Eric W. Biederman
2008-05-23 21:33 ` Bernhard Walle
0 siblings, 1 reply; 6+ messages in thread
From: Eric W. Biederman @ 2008-05-23 20:14 UTC (permalink / raw)
To: Sharyathi Nagesh
Cc: linux-kernel, fastboot, akpm, maneesh, mohan, sachinp, mohd.omar,
IndhuDurai, Kexec Mailing List
Sharyathi Nagesh <sharyath@in.ibm.com> writes:
> Hi
> While testing with kexec tool, I observed some problems. When application
> (kexec) is 32 bit and kernel is 64 bit I observed that loading crash kernel
> works without any issues but unloading crash kernel fails.
> --------------------------------------------------------
> running strace over 'kexec -u -p'
> show the problem to be with sys_kexec_load() call
>
> sys_kexec_load(0, 0, 0, 0x1, 0) = -1 EINVAL (Invalid argument)
> write(2, "kexec_load (0 segments) failed: "..., 49
> kexec_load (0 segments) failed: Invalid argument
> ) = 4
Yes. This is a bug. Although not in the kernel implementation.
> --------------------------------------------------------
>
> This is patch to fix the problem, I think kernel code had a typo where in:
> if((flags & KEXEC_ARCH_MASK) == KEXEC_ARCH) was used instead of
> if((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH)
Nope. We do the latter check after we have fixed up the arguments
and call sys_kexec_load. The check really is meant to filter out
KEXEC_ARCH_DEFAULT.
> This patch takes care of that, I have tested the patch it worked fine for
> me. Please review the patch and let me know of your views. This patch is based
> on linux-2.6.26-rc3.
That patch as it exists is actively bad. It removes the check for a really
nasty gotcha if someone passes in KEXEC_ARCH_DEFAULT in 32bit mode. Code
expecting a 32bit handoff and getting a 64bit handoff will explode in fun
ways. You happened to test the one corner case where this does not matter.
What we need to do is fix /sbin/kexec to pass in the correct
architecture of the kernel for unload as it does for load.
Eric
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: correction to compat_sys_kexec_load
2008-05-23 20:14 ` Eric W. Biederman
@ 2008-05-23 21:33 ` Bernhard Walle
2008-05-24 0:36 ` Eric W. Biederman
0 siblings, 1 reply; 6+ messages in thread
From: Bernhard Walle @ 2008-05-23 21:33 UTC (permalink / raw)
To: Eric W. Biederman
Cc: Sharyathi Nagesh, akpm, mohd.omar, IndhuDurai, Kexec Mailing List,
fastboot, linux-kernel, mohan, sachinp
[-- Attachment #1: Type: text/plain, Size: 609 bytes --]
* ebiederm@xmission.com (Eric W. Biederman) [2008-05-23 13:14]:
>
> What we need to do is fix /sbin/kexec to pass in the correct
> architecture of the kernel for unload as it does for load.
How should it know that it unloads a 32 bit kernel on a 64 bit system?
It doesn't have access to the kernel any more once it has been loaded.
Bernhard
PS: My mail server complains that maneesh@in.ltcfwd.linux.ibm.com is
invalid because "Recipient address rejected: Domain not found". Maybe
some of the other IBM guys in Cc can take a look at this ... I just
removed that address from Cc for now.
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 189 bytes --]
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: correction to compat_sys_kexec_load
2008-05-23 21:33 ` Bernhard Walle
@ 2008-05-24 0:36 ` Eric W. Biederman
2008-05-26 20:32 ` Bernhard Walle
0 siblings, 1 reply; 6+ messages in thread
From: Eric W. Biederman @ 2008-05-24 0:36 UTC (permalink / raw)
To: Bernhard Walle
Cc: Sharyathi Nagesh, akpm, mohd.omar, IndhuDurai, Kexec Mailing List,
fastboot, linux-kernel, mohan, sachinp
Bernhard Walle <bwalle@suse.de> writes:
> * ebiederm@xmission.com (Eric W. Biederman) [2008-05-23 13:14]:
>>
>> What we need to do is fix /sbin/kexec to pass in the correct
>> architecture of the kernel for unload as it does for load.
>
> How should it know that it unloads a 32 bit kernel on a 64 bit system?
> It doesn't have access to the kernel any more once it has been loaded.
The architecture parameter is the architecture of the running kernel
that implements sys_kexec_load.
Because it is a pain for testing and in general impossible we don't
change cpu modes during a kexec. So a 32bit caller of sys_kexec_load
will need to passing in different code if it is running on a 32bit or
a 64bit kernel.
The trampoline code in /sbin/kexec does change modes on x86 when
appropriate.
Caring if you know the architecture in the unload case is a bit
silly. As there is no real justification for it. At this
point getting user space fixed so that it works on older kernels
seems important.
Eric
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2008-05-28 4:39 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2008-05-23 11:36 correction to compat_sys_kexec_load Sharyathi Nagesh
2008-05-23 20:14 ` Eric W. Biederman
2008-05-23 21:33 ` Bernhard Walle
2008-05-24 0:36 ` Eric W. Biederman
2008-05-26 20:32 ` Bernhard Walle
2008-05-28 4:39 ` Sharyathi Nagesh
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox