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Message-ID: <alpine.LSU.2.21.2009251450260.13615@pobox.suse.cz>
Date: Fri, 25 Sep 2020 15:06:55 +0200 (CEST)
From: Miroslav Benes <mbenes@...e.cz>
To: Kristen Carlson Accardi <kristen@...ux.intel.com>
cc: keescook@...omium.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
arjan@...ux.intel.com, x86@...nel.org, linux-kernel@...r.kernel.org,
kernel-hardening@...ts.openwall.com, rick.p.edgecombe@...el.com,
live-patching@...r.kernel.org
Subject: Re: [PATCH v5 00/10] Function Granular KASLR
Hi Kristen,
On Wed, 23 Sep 2020, Kristen Carlson Accardi wrote:
> 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
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