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

[Anton Protopopov <a.s.protopopov@gmail.com>]

On 26/11/06 09:09PM, sashiko-bot@kernel.org wrote:
> 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.

Added KCSAN and UBSAN (just in case, neither is enabled in tests).

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