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charset=UTF-8 Date: Mon, 16 Dec 2024 18:39:36 +0100 Message-Id: Cc: "Alexei Starovoitov" , "Daniel Borkmann" , "John Fastabend" , "Andrii Nakryiko" , "Martin KaFai Lau" , "Song Liu" , "Yonghong Song" , "KP Singh" , "Stanislav Fomichev" , "Hao Luo" , "Jiri Olsa" , Subject: Re: [PATCH bpf v2 2/2] selftests/bpf: Test r0 bounds after BPF to BPF call with abnormal return From: "Arthur Fabre" To: "Eduard Zingerman" , X-Mailer: aerc 0.8.2 References: <20241213212717.1830565-1-afabre@cloudflare.com> <20241213212717.1830565-3-afabre@cloudflare.com> <76401f4502366c2d9221758f9034aa7bb2d831a3.camel@gmail.com> In-Reply-To: <76401f4502366c2d9221758f9034aa7bb2d831a3.camel@gmail.com> On Sat Dec 14, 2024 at 12:55 AM CET, Eduard Zingerman wrote: > On Fri, 2024-12-13 at 22:27 +0100, Arthur Fabre wrote: [...] > > +++ b/tools/testing/selftests/bpf/progs/verifier_abnormal_ret.c > > @@ -0,0 +1,88 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > + > > +#include > > +#include > > +#include "../../../include/linux/filter.h" > > +#include "bpf_misc.h" > > + > > +#define TEST(NAME, CALLEE) \ > > + SEC("socket") \ > > + __description("abnormal_ret: " #NAME) \ > > + __failure __msg("math between ctx pointer and register with unbounded= min value") \ > > + __naked void check_abnormal_ret_##NAME(void) \ > > + { \ > > Nit: this one and 'callee_tail_call' could be plain C. > > > + asm volatile(" \ > > + r6 =3D r1; \ > > + call " #CALLEE "; \ > > + r6 +=3D r0; \ > > + r0 =3D 0; \ > > + exit; \ > > + " : \ > > + : \ > > + : __clobber_all); \ > > + } > > [...] > > > +static __naked __noinline __used > > +int callee_tail_call(void) > > +{ > > + asm volatile(" \ > > + r2 =3D %[map_prog] ll; \ > > + r3 =3D 0; \ > > + call %[bpf_tail_call]; \ > > + r0 =3D 0; \ > > + exit; \ > > +" : > > + : __imm(bpf_tail_call), __imm_addr(map_prog) > > + : __clobber_all); > > +} > > + > > +char _license[] SEC("license") =3D "GPL"; Thanks for the review! Good point, I'll try to write them in C. It might not be possible to do them both entirely: clang also doesn't know that bpf_tail_call() can return, so it assumes the callee() will return a constant r0. It sometimes optimizes branches / loads out because of this.