Messages in this thread | | | Date | Mon, 19 Dec 2022 14:01:58 -0800 | Subject | Re: [PATCH bpf-next v2 2/2] selftests/bpf: check null propagation only neither reg is PTR_TO_BTF_ID | From | Martin KaFai Lau <> |
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On 12/12/22 7:04 PM, Hao Sun wrote: > Verify that nullness information is not porpagated in the branches > of register to register JEQ and JNE operations if one of them is > PTR_TO_BTF_ID.
Thanks for the fix and test.
> > Signed-off-by: Hao Sun <sunhao.th@gmail.com> > Acked-by: Yonghong Song <yhs@fb.com> > --- > .../bpf/verifier/jeq_infer_not_null.c | 22 +++++++++++++++++++ > 1 file changed, 22 insertions(+) > > diff --git a/tools/testing/selftests/bpf/verifier/jeq_infer_not_null.c b/tools/testing/selftests/bpf/verifier/jeq_infer_not_null.c > index 67a1c07ead34..b2b215227d97 100644 > --- a/tools/testing/selftests/bpf/verifier/jeq_infer_not_null.c > +++ b/tools/testing/selftests/bpf/verifier/jeq_infer_not_null.c > @@ -172,3 +172,25 @@ > .prog_type = BPF_PROG_TYPE_XDP, > .result = ACCEPT, > }, > +{ > + "jne/jeq infer not null, PTR_TO_MAP_OR_NULL unchanged with PTR_TO_BTF_ID reg", > + .insns = { > + BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), > + BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), > + BPF_ST_MEM(BPF_DW, BPF_REG_2, 0, 0), > + BPF_LD_MAP_FD(BPF_REG_1, 0), > + /* r6 = bpf_map->inner_map_meta; */ > + BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1, 8),
This bpf_map->inner_map_meta requires CO-RE. It works now but could be fragile in different platform and in the future bpf_map changes. Take a look at the map_ptr_kern.c which uses "__attribute__((preserve_access_index))" at the "struct bpf_map".
Please translate this verifer test into a proper bpf prog in C code such that it can use the CO-RE in libbpf. It should run under test_progs instead of test_verifier. The bpf prog can include the "vmlinux.h" to get the "__attribute__((preserve_access_index))" for free. Take a look at https://lore.kernel.org/all/20221207201648.2990661-2-andrii@kernel.org/ which has example on how to check verifier message in test_progs.
> + /* r0 = map_lookup_elem(r1, r2); */ > + BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem), > + /* if (r0 == r6) read *r0; */ > + BPF_JMP_REG(BPF_JEQ, BPF_REG_6, BPF_REG_0, 1), > + BPF_EXIT_INSN(), > + BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_0, 0), > + BPF_EXIT_INSN(), > + }, > + .fixup_map_hash_8b = { 3 }, > + .prog_type = BPF_PROG_TYPE_XDP, > + .result = REJECT, > + .errstr = "R0 invalid mem access 'map_value_or_null'", > +},
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