From 1271a40eeafa8e9b5b76c4d02e2b3812cbc3c280 Mon Sep 17 00:00:00 2001 From: KaFai Wan Date: Wed, 23 Apr 2025 20:13:28 +0800 Subject: [PATCH] bpf: Allow access to const void pointer arguments in tracing programs Adding support to access arguments with const void pointer arguments in tracing programs. Currently we allow tracing programs to access void pointers. If we try to access argument which is pointer to const void like 2nd argument in kfree, verifier will fail to load the program with; 0: R1=ctx() R10=fp0 ; asm volatile ("r2 = *(u64 *)(r1 + 8); "); 0: (79) r2 = *(u64 *)(r1 +8) func 'kfree' arg1 type UNKNOWN is not a struct Changing the is_int_ptr to void and generic integer check and renaming it to is_void_or_int_ptr. Signed-off-by: KaFai Wan Signed-off-by: Andrii Nakryiko Acked-by: Jiri Olsa Link: https://lore.kernel.org/bpf/20250423121329.3163461-2-mannkafai@gmail.com --- kernel/bpf/btf.c | 18 +++++++----------- 1 file changed, 7 insertions(+), 11 deletions(-) diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 656ee11aff67..a91822bae043 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -6383,12 +6383,11 @@ struct btf *bpf_prog_get_target_btf(const struct bpf_prog *prog) return prog->aux->attach_btf; } -static bool is_int_ptr(struct btf *btf, const struct btf_type *t) +static bool is_void_or_int_ptr(struct btf *btf, const struct btf_type *t) { /* skip modifiers */ t = btf_type_skip_modifiers(btf, t->type, NULL); - - return btf_type_is_int(t); + return btf_type_is_void(t) || btf_type_is_int(t); } static u32 get_ctx_arg_idx(struct btf *btf, const struct btf_type *func_proto, @@ -6776,14 +6775,11 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type, } } - if (t->type == 0) - /* This is a pointer to void. - * It is the same as scalar from the verifier safety pov. - * No further pointer walking is allowed. - */ - return true; - - if (is_int_ptr(btf, t)) + /* + * If it's a pointer to void, it's the same as scalar from the verifier + * safety POV. Either way, no futher pointer walking is allowed. + */ + if (is_void_or_int_ptr(btf, t)) return true; /* this is a pointer to another type */ -- 2.50.1