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From: Joe Lawrence <joe.lawrence@redhat.com>
To: Johannes Erdfelt <johannes@erdfelt.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	Jessica Yu <jeyu@kernel.org>, Jiri Kosina <jikos@kernel.org>,
	Miroslav Benes <mbenes@suse.cz>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@redhat.com>,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: Oops caused by race between livepatch and ftrace
Date: Tue, 21 May 2019 15:27:47 -0400	[thread overview]
Message-ID: <a2075a5b-e048-4a7b-2813-01ed7e75bde8@redhat.com> (raw)
In-Reply-To: <1802c0d2-702f-08ec-6a85-c7f887eb6d14@redhat.com>

On 5/20/19 5:19 PM, Joe Lawrence wrote:
> On 5/20/19 5:09 PM, Johannes Erdfelt wrote:
>> On Mon, May 20, 2019, Joe Lawrence <joe.lawrence@redhat.com> wrote:
>>> These two testing scenarios might be interesting to add to our selftests
>>> suite.  Can you post or add the source(s) to livepatch-test<n>.ko to the
>>> tarball?
>>
>> I made the livepatches using kpatch-build and this simple patch:
>>
>> diff --git a/fs/proc/version.c b/fs/proc/version.c
>> index 94901e8e700d..6b8a3449f455 100644
>> --- a/fs/proc/version.c
>> +++ b/fs/proc/version.c
>> @@ -12,6 +12,7 @@ static int version_proc_show(struct seq_file *m, void *v)
>>    		utsname()->sysname,
>>    		utsname()->release,
>>    		utsname()->version);
>> +	seq_printf(m, "example livepatch\n");
>>    	return 0;
>>    }
>>
>> I just created enough livepatches with the same source patch so that I
>> could reproduce the issue somewhat reliably.
>>
>> I'll see if I can make something that uses klp directly.
> 
> Ah ok great, I was hoping it was a relatively simply livepatch.  We
> could probably reuse lib/livepatch/test_klp_livepatch.c to do this
> (patching cmdline_proc_show instead).
> 
>> The rest of the userspace in the initramfs is really straight forward
>> with the only interesting parts being a couple of shell scripts.
> 
> Yup.  I'll be on PTO later this week, but I'll see about extracting the
> scripts and building a pile of livepatch .ko's to see how easily it
> reproduces without qemu.
> 

D'oh -- I just remembered that klp doesn't create those klp (arch) 
relocation sections just yet!  Without those, the window for module RO 
-> RW -> RO in klp_init_object_loaded is going to be really small... at 
least I can't reproduce it yet without those special sections.  So maybe 
such selftests need to wait post klp-convert.


BTW, livepatching folks -- speaking of this window, does it make sense 
for klp_init_object_loaded() to unconditionally frob the module section 
permissions?  Should it only bother iff it's going to apply 
relocations/alternatives/paravirt?

-- Joe

  reply	other threads:[~2019-05-21 19:28 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-20 19:49 Johannes Erdfelt
2019-05-20 20:46 ` Joe Lawrence
2019-05-20 21:09   ` Johannes Erdfelt
2019-05-20 21:19     ` Josh Poimboeuf
2019-05-20 21:39       ` Steven Rostedt
2019-05-21 14:16         ` Josh Poimboeuf
2019-05-21 14:42           ` Steven Rostedt
2019-05-21 16:42             ` Josh Poimboeuf
2019-05-21 16:53               ` Steven Rostedt
2019-05-29 11:17                 ` Jiri Kosina
2019-05-29 12:06                   ` Steven Rostedt
2019-05-29 12:30                     ` Josh Poimboeuf
2019-05-22 13:00               ` Josh Poimboeuf
2019-05-29 17:29               ` Jessica Yu
2019-05-29 17:39                 ` Josh Poimboeuf
2019-05-29 18:34                   ` Jessica Yu
2019-05-20 21:48       ` Johannes Erdfelt
2019-05-20 21:19     ` Joe Lawrence
2019-05-21 19:27       ` Joe Lawrence [this message]
2019-05-21 21:00         ` Josh Poimboeuf

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