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bpf: Forbid trampoline attach for functions with variable arguments

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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/

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210505132529.401047-1-jolsa@kernel.org
This commit is contained in:
Jiri Olsa 2021-05-05 15:25:29 +02:00 committed by Daniel Borkmann
parent 3b80d106e1
commit 31379397dc
1 changed files with 12 additions and 0 deletions
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12
kernel/bpf/btf.c
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@ -5206,6 +5206,12 @@ 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 +5219,12 @@ 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;