Since kernel version 5.4.217 LTS, there has been an issue with the kernel live patching feature becoming unavailable. When compiling the sample code for kernel live patching, the following message is displayed when enabled:
livepatch: klp_check_stack: kworker/u256:6:23490 has an unreliable stack
Reproduction steps: 1.git checkout v5.4.269 -b v5.4.269 2.make defconfig 3. Set CONFIG_LIVEPATCH=yćCONFIG_SAMPLE_LIVEPATCH=m 4. make -j bzImage 5. make samples/livepatch/livepatch-sample.ko 6. qemu-system-x86_64 -kernel arch/x86_64/boot/bzImage -nographic -append "console=ttyS0" -initrd initrd.img -m 1024M 7. insmod livepatch-sample.ko
Kernel live patch cannot complete successfully.
After some debugging, the immediate cause of the patch failure is an error in stack checking. The logs are as follows: [ 340.974853] livepatch: klp_check_stack: kworker/u256:0:23486 has an unreliable stack [ 340.974858] livepatch: klp_check_stack: kworker/u256:1:23487 has an unreliable stack [ 340.974863] livepatch: klp_check_stack: kworker/u256:2:23488 has an unreliable stack [ 340.974868] livepatch: klp_check_stack: kworker/u256:5:23489 has an unreliable stack [ 340.974872] livepatch: klp_check_stack: kworker/u256:6:23490 has an unreliable stack ......
BTW,if you use the v5.4.217 tag for testing, make sure to set CONFIG_RETPOLINE = y and CONFIG_LIVEPATCH = y, and other steps are consistent with v5.4.269
After investigation, The problem is strongly related to the commit 8afd1c7da2b0 ("x86/speculation: Change FILL_RETURN_BUFFER to work with objtool"), which would cause incorrect ORC entries to be generated, and the v5.4.217 version can undo this commit to make kernel livepatch work normally. It is a back-ported upstream patch with some code adjustments,from the git log, the author also mentioned no intra-function call validation support.
Based on commit 6e1f54a4985b63bc1b55a09e5e75a974c5d6719b (Linux 5.4.269), This patchset adds stack validation support for intra-function calls, allowing the kernel live patching feature to work correctly.
Alexandre Chartre (2): objtool: is_fentry_call() crashes if call has no destination objtool: Add support for intra-function calls
Rui Qi (1): x86/speculation: Support intra-function call validation
arch/x86/include/asm/nospec-branch.h | 7 ++ include/linux/frame.h | 11 ++++ .../Documentation/stack-validation.txt | 8 +++ tools/objtool/arch/x86/decode.c | 6 ++ tools/objtool/check.c | 64 +++++++++++++++++-- 5 files changed, 91 insertions(+), 5 deletions(-)