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Mon, 10 Aug 2026 11:56:27 -0700 (PDT) Message-ID: <3cc323f3c287b428d6b6451c707edaabfe5c865c.camel@gmail.com> Subject: Re: [PATCH bpf-next 6/6] selftests/bpf: Add arena fault tests for atomics with fetch From: Eduard Zingerman To: Daniel Borkmann , memxor@gmail.com Cc: puranjay@kernel.org, bpf@vger.kernel.org Date: Mon, 10 Aug 2026 11:56:24 -0700 In-Reply-To: <20260810134346.466004-6-daniel@iogearbox.net> References: <20260810134346.466004-1-daniel@iogearbox.net> <20260810134346.466004-6-daniel@iogearbox.net> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2-10 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2026-08-10 at 15:43 +0200, Daniel Borkmann wrote: > Add stream_arena_xchg_fault and stream_arena_cmpxchg_fault next to the > existing read, write and load-acquire fault tests, covering the two > places a read-modify-write can deposit the old value: src_reg for a > BPF_XCHG and r0 for a BPF_CMPXCHG. Both cover both halves of the JIT > bug that left the fetch destination alone when a RMW on an arena pointer > faulted: >=20 > =C2=A0 - the fault has to be reported as a WRITE, and at the address held= by > =C2=A0=C2=A0=C2=A0 the destination register, which __stderr() and test_ad= dress() check > =C2=A0 - the register receiving the fetched value has to be cleared by th= e > =C2=A0=C2=A0=C2=A0 fault handler, which the programs check by poisoning i= t before the > =C2=A0=C2=A0=C2=A0 atomic and returning it, so __retval(0) fails if it is= left untouched >=20 > Note, the atomics are open coded since linux/filter.h cannot be included > alongside vmlinux.h. >=20 > =C2=A0 # LDLIBS=3D-static PKG_CONFIG=3D'pkg-config --static' ./vmtest.sh = -- ./test_progs -t stream > =C2=A0 [...] > =C2=A0 #464/1=C2=A0=C2=A0 stream_arena_fault_address/read_fault:OK > =C2=A0 #464/2=C2=A0=C2=A0 stream_arena_fault_address/write_fault:OK > =C2=A0 #464/3=C2=A0=C2=A0 stream_arena_fault_address/load_acquire_fault:O= K > =C2=A0 #464/4=C2=A0=C2=A0 stream_arena_fault_address/xchg_fault:OK > =C2=A0 #464/5=C2=A0=C2=A0 stream_arena_fault_address/cmpxchg_fault:OK > =C2=A0 #464=C2=A0=C2=A0=C2=A0=C2=A0 stream_arena_fault_address:OK > =C2=A0 [...] > =C2=A0 #466/5=C2=A0=C2=A0 stream_success/stream_arena_write_fault:OK > =C2=A0 #466/6=C2=A0=C2=A0 stream_success/stream_arena_read_fault:OK > =C2=A0 #466/7=C2=A0=C2=A0 stream_success/stream_arena_load_acquire_fault:= OK > =C2=A0 #466/8=C2=A0=C2=A0 stream_success/stream_arena_xchg_fault:OK > =C2=A0 #466/9=C2=A0=C2=A0 stream_success/stream_arena_cmpxchg_fault:OK > =C2=A0 [...] > =C2=A0 Summary: 4/22 PASSED, 0 SKIPPED, 0 FAILED >=20 > Signed-off-by: Daniel Borkmann > --- Acked-by: Eduard Zingerman ... > diff --git a/tools/testing/selftests/bpf/prog_tests/stream.c b/tools/test= ing/selftests/bpf/prog_tests/stream.c > index 15dd3ae2a84b..e4e9374309e2 100644 > --- a/tools/testing/selftests/bpf/prog_tests/stream.c > +++ b/tools/testing/selftests/bpf/prog_tests/stream.c > @@ -105,6 +105,10 @@ void test_stream_arena_fault_address(void) > =C2=A0 test_address(skel->progs.stream_arena_write_fault, &skel->bss->fa= ult_addr); > =C2=A0 if (test__start_subtest("load_acquire_fault")) > =C2=A0 test_address(skel->progs.stream_arena_load_acquire_fault, &skel->= bss->fault_addr); > + if (test__start_subtest("xchg_fault")) > + test_address(skel->progs.stream_arena_xchg_fault, &skel->bss->fault_ad= dr); > + if (test__start_subtest("cmpxchg_fault")) > + test_address(skel->progs.stream_arena_cmpxchg_fault, &skel->bss->fault= _addr); Tbh, this seem to be an overkill. The point of these stream tests is to check the stream output format details etc. Here the __stderr annotation in the test already captures that the fault had happened and also checks retval. ...