Re: [PATCH v1 bpf-next 16/18] selftests/bpf: Test fmod_ret candidates found by bpf_scan_ir

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] selftests/bpf: missing KASAN and KCSAN exclusions for
  bpf_testmod_retval.o
--

commit 628c6eb28eaac0eeb5e557c0b787a65b02cd6e06
Author: Anton Protopopov <a.s.protopopov@gmail.com>

selftests/bpf: Test fmod_ret candidates found by bpf_scan_ir

This commit adds bpf_testmod fixtures and BPF selftests to verify the
fmod_ret target tags generated by the bpf_scan_ir compiler plugin and the
verifier's enforcement of restricted return values.

> diff --git a/tools/testing/selftests/bpf/test_kmods/Makefile b/tools/testing/selftests/bpf/test_kmods/Makefile
> index 031c7454ce65f..475df9a7680ea 100644
> --- a/tools/testing/selftests/bpf/test_kmods/Makefile
> +++ b/tools/testing/selftests/bpf/test_kmods/Makefile
> @@ -23,7 +23,16 @@ MODULES = bpf_testmod.ko bpf_test_no_cfi.ko bpf_test_modorder_x.ko \
>  
>  $(foreach m,$(MODULES),$(eval obj-m += $(m:.ko=.o)))
>  
> -CFLAGS_bpf_testmod.o = -I$(src)
> +bpf_testmod-y := bpf_testmod_main.o
> +# The functions for bpf_scan_ir use clang extensions and need the plugin
> +bpf_testmod-$(CONFIG_CLANG_PLUGIN_BPF_SCAN_IR) += bpf_testmod_retval.o \
> +						  bpf_testmod_retval_strong.o
> +# Coverage instrumentation makes every path of the fixtures dirty
> +GCOV_PROFILE_bpf_testmod_retval.o := n
> +KCOV_INSTRUMENT_bpf_testmod_retval.o := n
> +KMSAN_SANITIZE_bpf_testmod_retval.o := n

[Severity: Low]
Should KASAN_SANITIZE_bpf_testmod_retval.o and
KCSAN_SANITIZE_bpf_testmod_retval.o also be set to n here?

bpf_testmod_retval_private_store() and bpf_testmod_retval_private_memset()
use __attribute__((optnone)) to keep their stack writes and memset in the
IR until OptimizerLast.  When CONFIG_KASAN or CONFIG_KCSAN is enabled, the
sanitizer pass runs before bpf_scan_ir and instruments those operations
with shadow stores and runtime calls (__asan_report_store4, __asan_memset,
__tsan_write4), which bpf_scan_ir rejects as side effects, causing the tags
subtest in test_fmodret_retval() to fail.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261106205523.1765622-1-a.s.protopopov@gmail.com?part=16