[PATCH] bpf: Forbid trampoline attach for functions with variable arguments
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STALE2006d
LANDED
From: Jiri Olsa <jolsa@kernel.org>
Date: 2021-05-05 13:25:45
Also in:
bpf
Subsystem:
bpf [general] (safe dynamic programs and tools), the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Linus Torvalds
Status: Landed in mainline as 31379397dcc3 on 2021-05-06.
We can't currently allow to attach functions with variable arguments. The problem is that we should save all the registers for arguments, which is probably doable, but if caller uses more than 6 arguments, we need stack data, which will be wrong, because of the extra stack frame we do in bpf trampoline, so we could crash. Also currently there's malformed trampoline code generated for such functions at the moment as described in: https://lore.kernel.org/bpf/20210429212834.82621-1-jolsa@kernel.org/ (local) Signed-off-by: Jiri Olsa <jolsa@kernel.org> --- kernel/bpf/btf.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 0600ed325fa0..161511bb3e51 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c@@ -5206,6 +5206,13 @@ int btf_distill_func_proto(struct bpf_verifier_log *log, m->ret_size = ret; for (i = 0; i < nargs; i++) { + if (i == nargs - 1 && args[i].type == 0) { + bpf_log(log, + "The function %s with variable args is unsupported.\n", + tname); + return -EINVAL; + + } ret = __get_type_size(btf, args[i].type, &t); if (ret < 0) { bpf_log(log,
@@ -5213,6 +5220,12 @@ int btf_distill_func_proto(struct bpf_verifier_log *log, tname, i, btf_kind_str[BTF_INFO_KIND(t->info)]); return -EINVAL; } + if (ret == 0) { + bpf_log(log, + "The function %s has malformed void argument.\n", + tname); + return -EINVAL; + } m->arg_size[i] = ret; } m->nr_args = nargs;
--
2.30.2