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Sun, 16 Aug 2026 16:36:21 -0700 (PDT) Message-ID: <123a014b2b4ecd7d19cbdfe62c62d994e612b6f0.camel@gmail.com> Subject: Re: [PATCH bpf-next v2 2/2] selftests/bpf: Cover mixed arena and stack atomics From: Eduard Zingerman To: Yiyang Chen , Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , Shuah Khan , vineet.gupta@linux.dev Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Date: Sun, 16 Aug 2026 16:36:18 -0700 In-Reply-To: References: <20260816-bpf-next-038-mixed-atomic-v1-v2-0-4644c1886dbc@mails.tsinghua.edu.cn> <20260816-bpf-next-038-mixed-atomic-v1-v2-2-4644c1886dbc@mails.tsinghua.edu.cn> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2-10 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sun, 2026-08-16 at 16:17 -0700, Eduard Zingerman wrote: > On Sun, 2026-08-16 at 10:56 +0000, Yiyang Chen wrote: > > Add a verifier test with one atomic RMW instruction reached through > > PTR_TO_ARENA and PTR_TO_STACK paths. The verifier must reject the > > shared instruction with the existing incompatible-pointer diagnostic. > >=20 > > Signed-off-by: Yiyang Chen > > --- > > =C2=A0tools/testing/selftests/bpf/progs/verifier_arena.c | 39 +++++++++= +++++++++++++ > > =C2=A01 file changed, 39 insertions(+) > >=20 > > diff --git a/tools/testing/selftests/bpf/progs/verifier_arena.c b/tools= /testing/selftests/bpf/progs/verifier_arena.c > > index b241bbcf54a8a..b22bab33301ab 100644 > > --- a/tools/testing/selftests/bpf/progs/verifier_arena.c > > +++ b/tools/testing/selftests/bpf/progs/verifier_arena.c > > @@ -637,6 +637,45 @@ int non_arena_ptr_add_to_arena_ptr(void *ctx) > > =C2=A0 > > =C2=A0#endif > > =C2=A0 > > +static const struct bpf_insn addr_space_cast_insn =3D { > > + .code =3D 0xbf, > > + .dst_reg =3D BPF_REG_7, > > + .src_reg =3D BPF_REG_7, > > + .off =3D 1, > > + .imm =3D 1, > > +}; > > + > > +SEC("socket") > > +__description("arena and stack atomic at the same instruction") > > +__failure __msg("same insn cannot be used with different pointers") > > +__arch_x86_64 > > +__load_if_JITed() > > +__naked void mixed_arena_stack_atomic(void) > > +{ > > + asm volatile (" \ > > + r1 =3D %[arena] ll; \ > > + r6 =3D r10; \ > > + r6 +=3D -8; \ > > + r9 =3D 0; \ > > + *(u64 *)(r6 + 0) =3D r9; \ > > + r7 =3D 8192; \ > > + .8byte %[addr_space_cast]; \ >=20 > I'm going to fix this to: >=20 > r7 =3D addr_space_cast(r7, 0, 1); \ >=20 > as in the test case above. > Waiting for CI [1]. >=20 > [1] https://github.com/kernel-patches/bpf/pull/13325 A...and it requires another exception for GCC-BPF: https://github.com/kernel-patches/bpf/blob/bpf-next_base/ci/vmtest/configs/= DENYLIST.test_progs-bpf_gcc Ihor, it's a third time GCC-BPF strikes this weekend. What do people think about downgrading it to may-fail until the DENYLIST decreases to something reasonable? Anyway, I'll wrap-up with this patch-set in the evening. > > + call %[bpf_get_prandom_u32]; \ > > + if w0 !=3D 0 goto 1f; \ > > + r8 =3D r6; \ > > + goto 2f; \ > > +1: r8 =3D r7; \ > > +2: r9 =3D 1; \ > > + lock *(u64 *)(r8 + 0) +=3D r9; \ > > + r0 =3D 0; \ > > + exit; \ > > +" : > > + : __imm_addr(arena), > > + =C2=A0 __imm_insn(addr_space_cast, addr_space_cast_insn), > > + =C2=A0 __imm(bpf_get_prandom_u32) > > + : __clobber_all); > > +} > > + > > =C2=A0static __noinline > > =C2=A0u32 __arena *check_arena_arg_nonglobal(u32 __arena *arg) > > =C2=A0{