linux-kernel - Re: [PATCH v2] selftests: livepatch: Test atomic replace against multiple modules

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Date: Fri, 31 May 2024 15:44:46 -0400
From: Joe Lawrence <joe.lawrence@...hat.com>
To: Marcos Paulo de Souza <mpdesouza@...e.com>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, Jiri Kosina <jikos@...nel.org>,
	Miroslav Benes <mbenes@...e.cz>, Petr Mladek <pmladek@...e.com>,
	Shuah Khan <shuah@...nel.org>, live-patching@...r.kernel.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] selftests: livepatch: Test atomic replace against
 multiple modules

On Sat, May 25, 2024 at 11:34:08AM -0300, Marcos Paulo de Souza wrote:
> Adapt the current test-livepatch.sh script to account the number of
> applied livepatches and ensure that an atomic replace livepatch disables
> all previously applied livepatches.
> 
> Signed-off-by: Marcos Paulo de Souza <mpdesouza@...e.com>
> ---
> Changes since v1:
> * Added checks in the existing test-livepatch.sh instead of creating a
>   new test file. (Joe)
> * Fixed issues reported by ShellCheck (Joe)
> ---
>  .../testing/selftests/livepatch/test-livepatch.sh  | 46 ++++++++++++++++++++--
>  1 file changed, 42 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/testing/selftests/livepatch/test-livepatch.sh b/tools/testing/selftests/livepatch/test-livepatch.sh
> index e3455a6b1158..d85405d18e54 100755
> --- a/tools/testing/selftests/livepatch/test-livepatch.sh
> +++ b/tools/testing/selftests/livepatch/test-livepatch.sh
> @@ -107,9 +107,12 @@ livepatch: '$MOD_LIVEPATCH': unpatching complete
>  
>  # - load a livepatch that modifies the output from /proc/cmdline and
>  #   verify correct behavior
> -# - load an atomic replace livepatch and verify that only the second is active
> -# - remove the first livepatch and verify that the atomic replace livepatch
> -#   is still active
> +# - load two addtional livepatches and check the number of livepatch modules
> +#   applied
> +# - load an atomic replace livepatch and check that the other three modules were
> +#   disabled
> +# - remove all livepatches besides the atomic replace one and verify that the
> +#   atomic replace livepatch is still active
>  # - remove the atomic replace livepatch and verify that none are active
>  
>  start_test "atomic replace livepatch"
> @@ -119,12 +122,31 @@ load_lp $MOD_LIVEPATCH
>  grep 'live patched' /proc/cmdline > /dev/kmsg
>  grep 'live patched' /proc/meminfo > /dev/kmsg
>  
> +for mod in test_klp_syscall test_klp_callbacks_demo; do

Slightly nitpicky here, but the tests were originally written with the
livepatch module names via variables like $MOD_LIVEPATCH.  Would using
$MOD_LIVEPATCH{1,2,3} help indicate that their specifics aren't really
interesting, that we just need 3 of them?

> +	load_lp $mod
> +done
> +
> +mods=(/sys/kernel/livepatch/*)
> +nmods=${#mods[@]}
> +if [ "$nmods" -ne 3 ]; then
> +	die "Expecting three modules listed, found $nmods"
> +fi
> +

I was going to suggest that we might protect against a situation where
other livepatch modules were active, that a simple count wouldn't be
sufficient.  But then I thought about this test, atomic replace!
Anything previously loaded is going to be pushed aside anyway.

So maybe (in another patch or set) it would be worth enhancing
functions.sh :: start_test() do a quick sanity check to see that the
initial conditions are safe?  That might also prevent some collateral
damage when test A fails and leaves the world a strange place for tests
B, C, etc.

>  load_lp $MOD_REPLACE replace=1
>  
>  grep 'live patched' /proc/cmdline > /dev/kmsg
>  grep 'live patched' /proc/meminfo > /dev/kmsg
>  
> -unload_lp $MOD_LIVEPATCH
> +mods=(/sys/kernel/livepatch/*)
> +nmods=${#mods[@]}
> +if [ "$nmods" -ne 1 ]; then
> +	die "Expecting only one moduled listed, found $nmods"
> +fi
> +
> +# These modules were disabled by the atomic replace
> +for mod in test_klp_callbacks_demo test_klp_syscall $MOD_LIVEPATCH; do
> +	unload_lp "$mod"
> +done
>  
>  grep 'live patched' /proc/cmdline > /dev/kmsg
>  grep 'live patched' /proc/meminfo > /dev/kmsg
> @@ -142,6 +164,20 @@ livepatch: '$MOD_LIVEPATCH': starting patching transition
>  livepatch: '$MOD_LIVEPATCH': completing patching transition
>  livepatch: '$MOD_LIVEPATCH': patching complete
>  $MOD_LIVEPATCH: this has been live patched
> +% insmod test_modules/test_klp_syscall.ko

Similar minor nit here, too.  If we think copy/pasting all the $MOD_FOO
is annoying, I am fine with leaving this as is.  I don't have a strong
opinion other than following some convention.

With that, I'm happy to ack as-is or with variable names.

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

--
Joe