Hi,

On Fri, 2020-09-25 at 15:06 +0200, Miroslav Benes wrote:

Hi Kristen,

On Wed, 23 Sep 2020, Kristen Carlson Accardi wrote:

quoted

Function Granular Kernel Address Space Layout Randomization
(fgkaslr)
-----------------------------------------------------------------
----

This patch set is an implementation of finer grained kernel address
space
randomization. It rearranges your kernel code at load time 
on a per-function level granularity, with only around a second
added to
boot time.

I ran live patching kernel selftests on the patch set and everything 
passed fine.

However, we also use not-yet-upstream set of tests at SUSE for
testing 
live patching [1] and one of them, klp_tc_12.sh, is failing. You
should be 
able to run the set on upstream as is.

The test uninterruptedly sleeps in a kretprobed function called by a 
patched one. The current master without fgkaslr patch set reports
the 
stack of the sleeping task as unreliable and live patching fails.
The 
situation is different with fgkaslr (even with nofgkaslr on the
command 
line). The stack is returned as reliable. It looks something like 

[<0>] __schedule+0x465/0xa40
[<0>] schedule+0x55/0xd0
[<0>] orig_do_sleep+0xb1/0x110 [klp_test_support_mod]
[<0>] swap_pages+0x7f/0x7f

where the last entry is not reliable. I've seen 
kretprobe_trampoline+0x0/0x4a and some other symbols there too. Since
the 
patched function (orig_sleep_uninterruptible_set) is not on the
stack, 
live patching succeeds, which is not intended.

With kprobe setting removed, all works as expected.

So I wonder if there is still some issue with ORC somewhere as you 
mentioned in v4 thread. I'll investigate more next week, but wanted
to 
report early.

Regards
Miroslav

[1] https://github.com/lpechacek/qa_test_klp

Thanks for testing and reporting. I will grab your test and see what I
can find.