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Fri, 29 May 2026 10:03:14 -0700 (PDT) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Fri, 29 May 2026 13:03:13 -0400 Message-Id: Cc: , , , , , Subject: Re: [PATCH bpf 2/2] selftests/bpf: test fork on zero comparison with wrapping ranges From: "Emil Tsalapatis" To: "Eduard Zingerman" , , X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20260529-cnum-split-at-zero-v1-0-986c03752226@gmail.com> <20260529-cnum-split-at-zero-v1-2-986c03752226@gmail.com> In-Reply-To: <20260529-cnum-split-at-zero-v1-2-986c03752226@gmail.com> On Fri May 29, 2026 at 4:13 AM EDT, Eduard Zingerman wrote: > Add tests verifying that the verifier correctly narrows a > sign-boundary-crossing range after comparing with zero. > - fork_on_zero_cmp_k - BPF_K conditional instruction; > - fork_on_zero_cmp_x - > BPF_X conditional instruction with src being zero. > - fork_on_zero_cmp_x_swapped - > BPF_X conditional instruction with dst being zero. > Reviewed-by: Emil Tsalapatis > Signed-off-by: Eduard Zingerman > --- > .../testing/selftests/bpf/progs/verifier_bounds.c | 68 ++++++++++++++++= ++++++ > 1 file changed, 68 insertions(+) > > diff --git a/tools/testing/selftests/bpf/progs/verifier_bounds.c b/tools/= testing/selftests/bpf/progs/verifier_bounds.c > index bc038ac2df98..f97b0e109326 100644 > --- a/tools/testing/selftests/bpf/progs/verifier_bounds.c > +++ b/tools/testing/selftests/bpf/progs/verifier_bounds.c > @@ -2294,4 +2294,72 @@ __naked void range_within_cnum_cross_both_boundari= es(void) > : __clobber_all); > } > =20 > +SEC("socket") > +__success > +__naked void fork_on_zero_cmp_k(void) > +{ > + asm volatile (" \ > + call %[bpf_get_prandom_u32]; \ > + r0 &=3D 0xff; /* r0 =E2=88=88 [0, 255] */ \ > + r1 =3D 8; \ > + r1 -=3D r0; /* r1 =E2=88=88 [-247, 8] */ \ > + if r1 =3D=3D 0 goto 1f; \ > + if r1 > 8 goto 1f; /* r1 =E2=88=88 [1, 8] */ \ > + if r1 < 1 goto 2f; /* must be dead */ \ > + if r1 > 8 goto 2f; /* must be dead */ \ > + goto 1f; \ > +2: r0 /=3D 0; /* unreachable */ \ > +1: r0 =3D 0; \ > + exit; \ > + " > + :: __imm(bpf_get_prandom_u32) > + : __clobber_all); > +} > + > +SEC("socket") > +__success > +__naked void fork_on_zero_cmp_x(void) > +{ > + asm volatile (" \ > + call %[bpf_get_prandom_u32]; \ > + r0 &=3D 0xff; /* r0 =E2=88=88 [0, 255] */ \ > + r1 =3D 8; \ > + r1 -=3D r0; /* r1 =E2=88=88 [-247, 8] */ \ > + r2 =3D 0; \ > + if r1 =3D=3D r2 goto 1f; \ > + if r1 > 8 goto 1f; /* r1 =E2=88=88 [1, 8] */ \ > + if r1 < 1 goto 2f; /* must be dead */ \ > + if r1 > 8 goto 2f; /* must be dead */ \ > + goto 1f; \ > +2: r0 /=3D 0; /* unreachable */ \ > +1: r0 =3D 0; \ > + exit; \ > + " > + :: __imm(bpf_get_prandom_u32) > + : __clobber_all); > +} > + > +SEC("socket") > +__success > +__naked void fork_on_zero_cmp_x_swapped(void) > +{ > + asm volatile (" \ > + call %[bpf_get_prandom_u32]; \ > + r0 &=3D 0xff; /* r0 =E2=88=88 [0, 255] */ \ > + r1 =3D 8; \ > + r1 -=3D r0; /* r1 =E2=88=88 [-247, 8] */ \ > + r2 =3D 0; \ > + if r2 =3D=3D r1 goto 1f; \ > + if r1 > 8 goto 1f; /* r1 =E2=88=88 [1, 8] */ \ > + if r1 < 1 goto 2f; /* must be dead */ \ > + if r1 > 8 goto 2f; /* must be dead */ \ > + goto 1f; \ > +2: r0 /=3D 0; /* unreachable */ \ > +1: r0 =3D 0; \ > + exit; \ > + " > + :: __imm(bpf_get_prandom_u32) > + : __clobber_all); > +} > + > char _license[] SEC("license") =3D "GPL";