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bpf: Fix global subprog context argument resolution logic

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KPROBE program's user-facing context type is defined as typedef
bpf_user_pt_regs_t. This leads to a problem when trying to passing
kprobe/uprobe/usdt context argument into global subprog, as kernel
always strip away mods and typedefs of user-supplied type, but takes
expected type from bpf_ctx_convert as is, which causes mismatch.

Current way to work around this is to define a fake struct with the same
name as expected typedef:

  struct bpf_user_pt_regs_t {};

  __noinline my_global_subprog(struct bpf_user_pt_regs_t *ctx) { ... }

This patch fixes the issue by resolving expected type, if it's not
a struct. It still leaves the above work-around working for backwards
compatibility.

Fixes: 91cc1a9974 ("bpf: Annotate context types")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/20230216045954.3002473-2-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2023-02-15 20:59:52 -08:00 committed by Daniel Borkmann
parent 64f50f6575
commit d384dce281
1 changed files with 11 additions and 2 deletions
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13
kernel/bpf/btf.c
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@ -5669,6 +5669,7 @@ btf_get_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf,
if (!ctx_struct)
/* should not happen */
return NULL;
again:
ctx_tname = btf_name_by_offset(btf_vmlinux, ctx_struct->name_off);
if (!ctx_tname) {
/* should not happen */
@ -5682,8 +5683,16 @@ btf_get_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf,
* int socket_filter_bpf_prog(struct __sk_buff *skb)
* { // no fields of skb are ever used }
*/
if (strcmp(ctx_tname, tname))
return NULL;
if (strcmp(ctx_tname, tname)) {
/* bpf_user_pt_regs_t is a typedef, so resolve it to
* underlying struct and check name again
*/
if (!btf_type_is_modifier(ctx_struct))
return NULL;
while (btf_type_is_modifier(ctx_struct))
ctx_struct = btf_type_by_id(btf_vmlinux, ctx_struct->type);
goto again;
}
return ctx_type;
}