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Tue, 16 Jun 2026 14:14:14 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@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: Tue, 16 Jun 2026 17:14:12 -0400 Message-Id: Cc: "John Fastabend" , "Martin KaFai Lau" , "Luis Gerhorst" , "Shuah Khan" , , , Subject: Re: [PATCH bpf 2/2] selftests/bpf: Cover stack nospec slot indexing From: "Emil Tsalapatis" To: "Nuoqi Gui" , "Alexei Starovoitov" , "Daniel Borkmann" , "Andrii Nakryiko" , "Eduard Zingerman" , "Kumar Kartikeya Dwivedi" X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20260617-f01-11-stack-nospec-slot-index-v1-0-e3a080b0cd7e@mails.tsinghua.edu.cn> <20260617-f01-11-stack-nospec-slot-index-v1-2-e3a080b0cd7e@mails.tsinghua.edu.cn> In-Reply-To: <20260617-f01-11-stack-nospec-slot-index-v1-2-e3a080b0cd7e@mails.tsinghua.edu.cn> On Tue Jun 16, 2026 at 12:57 PM EDT, Nuoqi Gui wrote: > Add a verifier test for the fixed-offset stack write case where two 4-byt= e > stores initialize opposite halves of the same stack slot. > > The test uses the CAP_BPF-without-CAP_PERFMON loader lane so Spectre v4 > mitigation remains active. It expects both half-slot writes to emit nospe= c > in the translated program. > > Signed-off-by: Nuoqi Gui Reviewed-by: Emil Tsalapatis Trivial style nits. > --- > .../testing/selftests/bpf/progs/verifier_unpriv.c | 23 ++++++++++++++++= ++++++ > 1 file changed, 23 insertions(+) > > diff --git a/tools/testing/selftests/bpf/progs/verifier_unpriv.c b/tools/= testing/selftests/bpf/progs/verifier_unpriv.c > index c16f8382cf17d..9ebbd4b531df1 100644 > --- a/tools/testing/selftests/bpf/progs/verifier_unpriv.c > +++ b/tools/testing/selftests/bpf/progs/verifier_unpriv.c > @@ -976,4 +976,27 @@ l0_%=3D: exit; \ > : __clobber_all); > } > =20 > +SEC("socket") > +__description("noperfmon: Spectre v4 stack write slot index") > +__success __success_unpriv > +__caps_unpriv(CAP_BPF) > +__retval(0) > +#ifdef SPEC_V4 > +__xlated_unpriv("r0 =3D 0") > +__xlated_unpriv("*(u32 *)(r10 -4) =3D r0") > +__xlated_unpriv("nospec") > +__xlated_unpriv("*(u32 *)(r10 -8) =3D r0") No whitespace to the right of - > +__xlated_unpriv("nospec") > +__xlated_unpriv("exit") > +#endif > +__naked void stack_write_nospec_slot_index(void) > +{ > + asm volatile (" \ > + r0 =3D 0; \ > + *(u32 *)(r10 - 4) =3D r0; \ > + *(u32 *)(r10 - 8) =3D r0; \ Unaligned \=20 > + exit; \ > +" ::: __clobber_all); > +} > + > char _license[] SEC("license") =3D "GPL";