Re: [PATCH v5 00/10] Function Granular KASLR

[Kristen Carlson Accardi]

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.