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SubjectRe: [PATCH v5 00/10] Function Granular KASLR
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Date
Hi,

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

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


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