[PATCH v2 0/2] selftests/livepatch: fix building and running outside the host kernel

[PATCH v2 0/2] selftests/livepatch: fix building and running outside the host kernel

[Sasha Levin]

The livepatch test modules are built against the running host kernel
even when the selftests are built for a kernel in an output directory,
and the scripts skip every test on a machine without a kernel build
tree, even when the modules were built and installed with the
selftests.

Patch 1 is unchanged from v1. It picks KDIR from O or KBUILD_OUTPUT,
stops passing O and KBUILD_OUTPUT on to the module build, and skips the
modules for kernels without CONFIG_LIVEPATCH.

Patch 2 is new. Sashiko pointed out on v1 that has_kdir() skips the
tests on installed targets. That check predates this series, but it is
the run time half of the same problem, so patch 2 checks for the test
modules instead.

Tested on v7.4-rc1 with an x86_64 kernel with CONFIG_LIVEPATCH built in
an output directory. The modules build against it with

  make -C tools/testing/selftests O=... TARGETS=livepatch install

and the installed tree was run in a VM that has no build directory for
that kernel. Without patch 2 every test skips on the missing KDIR. With
it all 8 livepatch tests pass, and they skip cleanly when test_modules/
is missing.

Changes since v1:
- Add patch 2.
- Rebase on v7.4-rc1, no changes to patch 1.

v1: https://lore.kernel.org/all/20261014200154.1365200-1-sashal@kernel.org/

Sasha Levin (2):
  selftests/livepatch: build test modules against the selected kernel
  selftests/livepatch: skip based on the test modules instead of KDIR

 tools/testing/selftests/livepatch/Makefile    | 27 +++++++++++++++++++
 .../testing/selftests/livepatch/functions.sh  | 17 +++++-------
 .../selftests/livepatch/test_modules/Makefile |  6 +++--
 3 files changed, 37 insertions(+), 13 deletions(-)

-- 
2.53.0

[PATCH v2 1/2] selftests/livepatch: build test modules against the selected kernel

[Sasha Levin]

The livepatch test modules are built against /lib/modules/$(uname -r)/build
unless KDIR is set, and they are built unconditionally. This has three
problems:

- When the selftests are built for a kernel in an output directory
  (make O=...), the modules are still built against the running host
  kernel, or fail when the host has no build directory.

- The top-level selftests Makefile passes O to every suite, and the
  test_modules Makefile hands it on to the kernel build. Even an empty
  O= on the command line overrides the KBUILD_OUTPUT set by the
  Makefile of a kernel build directory, so the build fails against
  output directories and distribution headers such as Debian's:
  "make -C tools/testing/selftests TARGETS=livepatch" builds no
  modules at all.

- A kernel configured without CONFIG_LIVEPATCH cannot build the
  modules, although the installed scripts would correctly skip.

Select KDIR from O or KBUILD_OUTPUT when it is a prepared kernel build
directory containing Module.symvers, then from the source tree when the
kernel was built in place, and otherwise from the running kernel. An
explicit KDIR still takes precedence. Pass KDIR to test_modules as an
absolute path and stop forwarding O and KBUILD_OUTPUT to the kernel
build, including when the selftests are built through the kernel's
kselftest targets, since KDIR already names the output directory.

Read CONFIG_LIVEPATCH from the selected .config and skip the modules
only when the configuration is readable and the option is not enabled.
A KDIR without a readable configuration still attempts the build, so
that a directory that is not a prepared kernel tree fails the build
instead of silently producing an installation without modules. A KDIR
that does not exist keeps being skipped, as before.
Always clean test_modules, and have the scripts report a skip after the
root check when the running kernel does not provide livepatch.

Fixes: c4bbe83d27c2 ("livepatch: Move tests from lib/livepatch to selftests/livepatch")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 tools/testing/selftests/livepatch/Makefile    | 27 +++++++++++++++++++
 .../testing/selftests/livepatch/functions.sh  |  1 +
 .../selftests/livepatch/test_modules/Makefile |  6 +++--
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/livepatch/Makefile b/tools/testing/selftests/livepatch/Makefile
index a080eb54a215d..855bbad241235 100644
--- a/tools/testing/selftests/livepatch/Makefile
+++ b/tools/testing/selftests/livepatch/Makefile
@@ -1,7 +1,25 @@
 # SPDX-License-Identifier: GPL-2.0
 
+ifndef KDIR
+LIVEPATCH_OBJTREE := $(firstword $(O) $(KBUILD_OUTPUT))
+ifneq ($(and $(LIVEPATCH_OBJTREE),$(wildcard $(LIVEPATCH_OBJTREE)/Module.symvers)),)
+KDIR := $(LIVEPATCH_OBJTREE)
+else ifneq ($(wildcard ../../../../Module.symvers),)
+KDIR := ../../../..
+else
+KDIR := /lib/modules/$(shell uname -r)/build
+endif
+endif
+override KDIR := $(abspath $(KDIR))
+export KDIR
+
+LIVEPATCH_CONFIG := $(shell if [ -r "$(KDIR)/.config" ]; then \
+	grep -qx 'CONFIG_LIVEPATCH=y' "$(KDIR)/.config" && echo y || echo n; fi)
+
 TEST_GEN_FILES := test_klp-call_getpid
+ifneq ($(LIVEPATCH_CONFIG),n)
 TEST_GEN_MODS_DIR := test_modules
+endif
 TEST_PROGS_EXTENDED := functions.sh
 TEST_PROGS := \
 	test-livepatch.sh \
@@ -16,3 +34,12 @@ TEST_PROGS := \
 TEST_FILES := settings
 
 include ../lib.mk
+
+ifeq ($(LIVEPATCH_CONFIG),n)
+clean: clean_livepatch_mods
+
+clean_livepatch_mods:
+	$(Q)$(MAKE) -C test_modules clean
+
+.PHONY: clean_livepatch_mods
+endif
diff --git a/tools/testing/selftests/livepatch/functions.sh b/tools/testing/selftests/livepatch/functions.sh
index 429fce1f31431..8b26b70f92d8c 100644
--- a/tools/testing/selftests/livepatch/functions.sh
+++ b/tools/testing/selftests/livepatch/functions.sh
@@ -150,6 +150,7 @@ function cleanup() {
 #		 the ftrace_enabled sysctl.
 function setup_config() {
 	is_root
+	[[ -d "$SYSFS_KLP_DIR" ]] || skip "livepatch is not available"
 	has_kdir
 	push_config
 	set_dynamic_debug
diff --git a/tools/testing/selftests/livepatch/test_modules/Makefile b/tools/testing/selftests/livepatch/test_modules/Makefile
index a13d398585dcb..1fbeaac9c2b2c 100644
--- a/tools/testing/selftests/livepatch/test_modules/Makefile
+++ b/tools/testing/selftests/livepatch/test_modules/Makefile
@@ -16,14 +16,16 @@ obj-m += test_klp_atomic_replace.o \
 	test_klp_state3.o \
 	test_klp_syscall.o
 
+modules clean: MAKEOVERRIDES := $(filter-out O=% KBUILD_OUTPUT=%,$(MAKEOVERRIDES))
+
 # Ensure that KDIR exists, otherwise skip the compilation
 modules:
 ifneq ("$(wildcard $(KDIR))", "")
-	$(Q)$(MAKE) -C $(KDIR) modules KBUILD_EXTMOD=$(TESTMODS_DIR)
+	$(Q)env -u KBUILD_OUTPUT $(MAKE) -C $(KDIR) modules KBUILD_EXTMOD=$(TESTMODS_DIR)
 endif
 
 # Ensure that KDIR exists, otherwise skip the clean target
 clean:
 ifneq ("$(wildcard $(KDIR))", "")
-	$(Q)$(MAKE) -C $(KDIR) clean KBUILD_EXTMOD=$(TESTMODS_DIR)
+	$(Q)env -u KBUILD_OUTPUT $(MAKE) -C $(KDIR) clean KBUILD_EXTMOD=$(TESTMODS_DIR)
 endif
-- 
2.53.0

Re: [PATCH v2 1/2] selftests/livepatch: build test modules against the selected kernel

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] selftests/livepatch: clean fails to resolve LIVEPATCH_OBJTREE
- [Medium] selftests/livepatch: relative command-line KDIR not resolved for sub-make
--

commit 02a5cf889b06dba8630406e570f3de0adc2db5d6
Author: Sasha Levin <sashal@kernel.org>

selftests/livepatch: build test modules against the selected kernel

This commit updates the livepatch selftest Makefiles to select KDIR from O,
KBUILD_OUTPUT, or the in-tree build before falling back to the running
kernel's build directory. It also skips building test modules when
CONFIG_LIVEPATCH is disabled in the target .config and stops forwarding O and
KBUILD_OUTPUT to the external module build.

> diff --git a/tools/testing/selftests/livepatch/Makefile b/tools/testing/selftests/livepatch/Makefile
> index a080eb54a215d..855bbad241235 100644
> --- a/tools/testing/selftests/livepatch/Makefile
> +++ b/tools/testing/selftests/livepatch/Makefile
> @@ -1,7 +1,25 @@
>  # SPDX-License-Identifier: GPL-20
>  
> +ifndef KDIR
> +LIVEPATCH_OBJTREE := $(firstword $(O) $(KBUILD_OUTPUT))
> +ifneq ($(and $(LIVEPATCH_OBJTREE),$(wildcard $(LIVEPATCH_OBJTREE)/Module.symvers)),)
> +KDIR := $(LIVEPATCH_OBJTREE)
> +else ifneq ($(wildcard ../../../../Module.symvers),)
> +KDIR := ../../../..
> +else
> +KDIR := /lib/modules/$(shell uname -r)/build
> +endif
> +endif

[Severity: Medium]
Can this fail to locate the build directory during a clean when a relative
O= or KBUILD_OUTPUT= path is used, or when the kernel build tree has already
removed Module.symvers?

During all, run_tests, and install, tools/testing/selftests/Makefile resolves
O and KBUILD_OUTPUT into abs_objtree and passes O=$(abs_objtree) to the
target sub-makes, but the clean target does not pass O=$(abs_objtree):

tools/testing/selftests/Makefile:
clean:
	@for TARGET in $(TARGETS) $(INSTALL_DEP_TARGETS); do \
		BUILD_TARGET=$$BUILD/$$TARGET;	\
		$(MAKE) OUTPUT=$$BUILD_TARGET -C $$TARGET clean;\
	done;

When running "make O=build kselftest-clean TARGETS=livepatch" or
"make -C tools/testing/selftests O=build TARGETS=livepatch clean",
LIVEPATCH_OBJTREE in tools/testing/selftests/livepatch/Makefile receives the
unanchored relative path "build" (via MAKEFLAGS or the KBUILD_OUTPUT
environment variable) and checks for tools/testing/selftests/livepatch/build/Module.symvers
instead of ../../../../build/Module.symvers.

Similarly, if the kernel build directory was cleaned before kselftest-clean,
Module.symvers is already gone even though Kbuild external-module clean does
not require it.

In both cases, KDIR falls back to /lib/modules/$(shell uname -r)/build. On a
host or container where /lib/modules/$(uname -r)/build does not exist,
tools/testing/selftests/livepatch/test_modules/Makefile sees an empty
$(wildcard $(KDIR)) and skips cleaning test_modules/, leaving the built
module artifacts behind.

> +override KDIR := $(abspath $(KDIR))
> +export KDIR

[Severity: Medium]
Does passing a relative KDIR=... on the make command line still propagate the
unresolved relative path to test_modules/Makefile?

In GNU Make, "override KDIR := $(abspath $(KDIR))" and "export KDIR" update
KDIR in the current makefile and exported environment, but the original
command-line assignment remains in MAKEOVERRIDES (forwarded via MAKEFLAGS).

When ../lib.mk (via gen_mods_dir or clean_mods_dir) or clean_livepatch_mods
invokes $(MAKE) -C test_modules, the sub-make in
tools/testing/selftests/livepatch/test_modules/Makefile only filters O=% and
KBUILD_OUTPUT=% out of MAKEOVERRIDES:

tools/testing/selftests/livepatch/test_modules/Makefile:
modules clean: MAKEOVERRIDES := $(filter-out O=% KBUILD_OUTPUT=%,$(MAKEOVERRIDES))

As a result, the child make inherits the raw command-line KDIR=<relative_path>
from MAKEFLAGS, which takes precedence over the exported environment variable
and is evaluated one directory deeper inside test_modules/ (for example,
"make -C tools/testing/selftests/livepatch KDIR=../../../.." resolves KDIR to
tools/ inside test_modules/Makefile and fails the build, or silently skips
building if the shifted path does not exist).

Should KDIR=% also be filtered out of MAKEOVERRIDES (or passed explicitly as
KDIR=$(KDIR) to the test_modules sub-make)?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261103140218.17568-1-sashal@kernel.org?part=1

[PATCH v2 2/2] selftests/livepatch: skip based on the test modules instead of KDIR

[Sasha Levin]

setup_config() skips every test when there is no kernel build directory
at $KDIR or /lib/modules/$(uname -r)/build. The test modules are built
together with the selftests and the scripts load them from
test_modules/, so nothing needs a build directory at run time. A
machine running an installed kselftest tree usually has none, and the
tests are skipped there although the modules were built and installed.

Check for the modules that __load_mod() loads instead, and remove
has_kdir(), which has no other users.

Fixes: 54ee3526796f ("selftests: livepatch: Avoid running the tests if kernel-devel is missing")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 tools/testing/selftests/livepatch/functions.sh | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/livepatch/functions.sh b/tools/testing/selftests/livepatch/functions.sh
index 8b26b70f92d8c..14fc9cade4de3 100644
--- a/tools/testing/selftests/livepatch/functions.sh
+++ b/tools/testing/selftests/livepatch/functions.sh
@@ -44,16 +44,10 @@ function is_root() {
 	fi
 }
 
-# Check if we can compile the modules before loading them
-function has_kdir() {
-	if [ -z "$KDIR" ]; then
-		KDIR="/lib/modules/$(uname -r)/build"
-	fi
-
-	if [ ! -d "$KDIR" ]; then
-		echo "skip all tests: KDIR ($KDIR) not available to compile modules."
-		exit $ksft_skip
-	fi
+# Check that the test modules were built before loading them
+function has_test_modules() {
+	compgen -G "test_modules/*.ko" > /dev/null ||
+		skip "test modules are not available"
 }
 
 # die(msg) - game over, man
@@ -151,7 +145,7 @@ function cleanup() {
 function setup_config() {
 	is_root
 	[[ -d "$SYSFS_KLP_DIR" ]] || skip "livepatch is not available"
-	has_kdir
+	has_test_modules
 	push_config
 	set_dynamic_debug
 	set_ftrace_enabled 1
-- 
2.53.0