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([2620:10d:c090:500::4:e681]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-33c33188f76sm319160eec.21.2026.09.18.11.15.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Sep 2026 11:15:43 -0700 (PDT) Message-ID: <4599bf823fbe81380ca7980a2d60283ca73e28aa.camel@gmail.com> Subject: Re: [PATCH bpf v2 2/2] selftests/bpf: Cover frame changes in bounded loops From: Eduard Zingerman To: Kumar Kartikeya Dwivedi , bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Emil Tsalapatis , Nicholas Carlini , kkd@meta.com, kernel-team@meta.com Date: Fri, 18 Sep 2026 11:15:41 -0700 In-Reply-To: <20260918011313.3053497-3-memxor@gmail.com> References: <20260918011313.3053497-1-memxor@gmail.com> <20260918011313.3053497-3-memxor@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-1.fc44) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2026-09-18 at 03:13 +0200, Kumar Kartikeya Dwivedi wrote: > Add two finite loops whose progress is represented only by changing the > frame number of a stack pointer. Each loop first reads zero from the > caller's stack, switches to the same offset in the callee's stack, and > exits after reading one on its next iteration. >=20 > Keep the pointer in a register in one test and spill it in the other to > exercise both regsafe() and stacksafe() during exact state comparison. > Force frequent checkpoints so the tests exercise infinite-loop detection, > and check that both programs return one when run. >=20 > Without the frameno comparison in regs_exact(), both programs are > rejected with an "infinite loop detected" diagnostic instead of loading > successfully. >=20 > Signed-off-by: Kumar Kartikeya Dwivedi > --- Tested-by: Eduard Zingerman > .../selftests/bpf/progs/verifier_loops1.c | 70 +++++++++++++++++++ > 1 file changed, 70 insertions(+) >=20 > diff --git a/tools/testing/selftests/bpf/progs/verifier_loops1.c b/tools/= testing/selftests/bpf/progs/verifier_loops1.c > index d248ce877f14..ada7e1105a95 100644 > --- a/tools/testing/selftests/bpf/progs/verifier_loops1.c > +++ b/tools/testing/selftests/bpf/progs/verifier_loops1.c > @@ -303,4 +303,74 @@ __naked void maybe_exit_scc_bug1(void) > ::: __clobber_all); > } > =20 > +/* > + * The loop reads zero from the caller's stack on its first iteration an= d > + * one from the callee's stack on its second iteration. At the loop head= er, > + * only the frame number of the pointer in r1 changes. > + */ > +static __naked __noinline __used > +void loop_stack_frames_reg(void) > +{ > + asm volatile ( > + "*(u64 *)(r10 - 8) =3D 1;" > + "1: r0 =3D *(u64 *)(r1 + 0);" Nit: please use formatting as below: "1:" "r0 =3D *(u64 *)(r1 + 0);" > + "if r0 !=3D 0 goto 2f;" > + "r1 =3D r10;" > + "r1 +=3D -8;" > + "goto 1b;" > + "2: exit;" > + ::: __clobber_all); > +} > + > +SEC("xdp") > +__description("bounded loop changing stack frame in a register") > +__success __retval(1) > +__flag(BPF_F_TEST_STATE_FREQ) > +__naked void bounded_loop_stack_frames_reg(void) > +{ > + asm volatile ( > + "*(u64 *)(r10 - 8) =3D 0;" > + "r1 =3D r10;" > + "r1 +=3D -8;" > + "call loop_stack_frames_reg;" > + "exit;" > + ::: __clobber_all); > +} --- 8< --- > +/* > + * Exercise the same frame change through a spilled pointer. All registe= rs > + * at the loop header are identical, while fp-16 points to a different f= rame. > + */ > +static __naked __noinline __used > +void loop_stack_frames_spill(void) > +{ > + asm volatile ( > + "*(u64 *)(r10 - 8) =3D 1;" > + "*(u64 *)(r10 - 16) =3D r1;" > + "1: r1 =3D *(u64 *)(r10 - 16);" > + "r0 =3D *(u64 *)(r1 + 0);" > + "if r0 !=3D 0 goto 2f;" > + "r1 =3D r10;" > + "r1 +=3D -8;" > + "*(u64 *)(r10 - 16) =3D r1;" > + "goto 1b;" > + "2: exit;" > + ::: __clobber_all); > +} > + > +SEC("xdp") > +__description("bounded loop changing stack frame in a spill") > +__success __retval(1) > +__flag(BPF_F_TEST_STATE_FREQ) > +__naked void bounded_loop_stack_frames_spill(void) > +{ > + asm volatile ( > + "*(u64 *)(r10 - 8) =3D 0;" > + "r1 =3D r10;" > + "r1 +=3D -8;" > + "call loop_stack_frames_spill;" > + "exit;" > + ::: __clobber_all); > +} > + > char _license[] SEC("license") =3D "GPL"; I think this test is redundant, existing tests should already cover the chain stack_safe -> regsafe. --- >8 ---