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

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Date:   Tue, 22 Feb 2022 10:34:57 -0500
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Petr Mladek <pmladek@...e.com>, 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,
        corbet@....net, kernel-team@...com
Subject: Re: [PATCH v3] livepatch: Skip livepatch tests if ftrace cannot be
 configured

On 2/21/22 9:13 AM, Petr Mladek wrote:
> 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>
> 
> Reviewed-by: Petr Mladek <pmladek@...e.com>
> Tested-by: Petr Mladek <pmladek@...e.com>
> 
> I am going to push it after two days or so unless anyone is against.
> 

Sorry for late replies as I'm just back from PTO, but v3 looks good to
me.  Thanks Petr and David.

Acked-by: Joe Lawrence <joe.lawrence@...hat.com>

-- 
Joe