linux-kernel - Re: [PATCH v3] livepatch: Skip livepatch tests if ftrace cannot be configured

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Date:   Thu, 24 Feb 2022 10:08:06 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     David Vernet <void@...ifault.com>
Cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        jpoimboe@...hat.com, jikos@...nel.org, mbenes@...e.cz,
        joe.lawrence@...hat.com, corbet@....net, kernel-team@...com
Subject: Re: [PATCH v3] livepatch: Skip livepatch tests if ftrace cannot be
 configured

On Wed 2022-02-16 08:11:01, David Vernet wrote:
> livepatch has a set of selftests that are used to validate the behavior of
> the livepatching subsystem.  One of the testcases in the livepatch
> testsuite is test-ftrace.sh, which among other things, validates that
> livepatching gracefully fails when ftrace is disabled.  In the event that
> ftrace cannot be disabled using 'sysctl kernel.ftrace_enabled=0', the test
> will fail later due to it unexpectedly successfully loading the
> test_klp_livepatch module.
> 
> While the livepatch selftests are careful to remove any of the livepatch
> test modules between testcases to avoid this situation, ftrace may still
> fail to be disabled if another trace is active on the system that was
> enabled with FTRACE_OPS_FL_PERMANENT.  For example, any active BPF programs
> that use trampolines will cause this test to fail due to the trampoline
> being implemented with register_ftrace_direct().  The following is an
> example of such a trace:
> 
> tcp_drop (1) R I D      tramp: ftrace_regs_caller+0x0/0x58
> (call_direct_funcs+0x0/0x30)
>         direct-->bpf_trampoline_6442550536_0+0x0/0x1000
> 
> In order to make the test more resilient to system state that is out of its
> control, this patch updates set_ftrace_enabled() to detect sysctl failures,
> and skip the testrun when appropriate.
> 
> Suggested-by: Petr Mladek <pmladek@...e.com>
> Signed-off-by: David Vernet <void@...ifault.com>

The patch has been committed into livepatch/livepatch.git,
branch for-5.18/selftests-fixes.

Best Regards,
Petr