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livepatch: Skip livepatch tests if ftrace cannot be configured

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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@suse.com>
Signed-off-by: David Vernet <void@manifault.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220216161100.3243100-1-void@manifault.com
This commit is contained in:
David Vernet 2022-02-16 08:11:01 -08:00 committed by Petr Mladek
parent 77dbd72b98
commit 4327b9eaf8
2 changed files with 21 additions and 4 deletions
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22
tools/testing/selftests/livepatch/functions.sh
View File

@ -75,9 +75,25 @@ function set_dynamic_debug() {
}
function set_ftrace_enabled() {
result=$(sysctl -q kernel.ftrace_enabled="$1" 2>&1 && \
sysctl kernel.ftrace_enabled 2>&1)
echo "livepatch: $result" > /dev/kmsg
local can_fail=0
if [[ "$1" == "--fail" ]] ; then
can_fail=1
shift
fi
local err=$(sysctl -q kernel.ftrace_enabled="$1" 2>&1)
local result=$(sysctl --values kernel.ftrace_enabled)
if [[ "$result" != "$1" ]] ; then
if [[ $can_fail -eq 1 ]] ; then
echo "livepatch: $err" > /dev/kmsg
return
fi
skip "failed to set kernel.ftrace_enabled = $1"
fi
echo "livepatch: kernel.ftrace_enabled = $result" > /dev/kmsg
}
function cleanup() {

3
tools/testing/selftests/livepatch/test-ftrace.sh
View File

@ -25,7 +25,8 @@ if [[ "$(cat /proc/cmdline)" != "$MOD_LIVEPATCH: this has been live patched" ]]
die "livepatch kselftest(s) failed"
fi
set_ftrace_enabled 0
# Check that ftrace could not get disabled when a livepatch is enabled
set_ftrace_enabled --fail 0
if [[ "$(cat /proc/cmdline)" != "$MOD_LIVEPATCH: this has been live patched" ]] ; then
echo -e "FAIL\n\n"
die "livepatch kselftest(s) failed"