From a687df2008f66669deec27f74d1793c8a537a4bd Mon Sep 17 00:00:00 2001 From: Amery Hung Date: Mon, 17 Feb 2025 11:06:37 -0800 Subject: bpf: Support getting referenced kptr from struct_ops argument Allows struct_ops programs to acqurie referenced kptrs from arguments by directly reading the argument. The verifier will acquire a reference for struct_ops a argument tagged with "__ref" in the stub function in the beginning of the main program. The user will be able to access the referenced kptr directly by reading the context as long as it has not been released by the program. This new mechanism to acquire referenced kptr (compared to the existing "kfunc with KF_ACQUIRE") is introduced for ergonomic and semantic reasons. In the first use case, Qdisc_ops, an skb is passed to .enqueue in the first argument. This mechanism provides a natural way for users to get a referenced kptr in the .enqueue struct_ops programs and makes sure that a qdisc will always enqueue or drop the skb. Signed-off-by: Amery Hung Acked-by: Eduard Zingerman Acked-by: Martin KaFai Lau Link: https://lore.kernel.org/r/20250217190640.1748177-3-ameryhung@gmail.com Signed-off-by: Alexei Starovoitov --- kernel/bpf/bpf_struct_ops.c | 27 +++++++++++++++++++++------ 1 file changed, 21 insertions(+), 6 deletions(-) (limited to 'kernel/bpf/bpf_struct_ops.c') diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c index 9b7f3b9c5262..0ef00f7f64c9 100644 --- a/kernel/bpf/bpf_struct_ops.c +++ b/kernel/bpf/bpf_struct_ops.c @@ -146,6 +146,7 @@ void bpf_struct_ops_image_free(void *image) } #define MAYBE_NULL_SUFFIX "__nullable" +#define REFCOUNTED_SUFFIX "__ref" /* Prepare argument info for every nullable argument of a member of a * struct_ops type. @@ -174,11 +175,13 @@ static int prepare_arg_info(struct btf *btf, struct bpf_struct_ops_arg_info *arg_info) { const struct btf_type *stub_func_proto, *pointed_type; + bool is_nullable = false, is_refcounted = false; const struct btf_param *stub_args, *args; struct bpf_ctx_arg_aux *info, *info_buf; u32 nargs, arg_no, info_cnt = 0; char ksym[KSYM_SYMBOL_LEN]; const char *stub_fname; + const char *suffix; s32 stub_func_id; u32 arg_btf_id; int offset; @@ -223,10 +226,18 @@ static int prepare_arg_info(struct btf *btf, info = info_buf; for (arg_no = 0; arg_no < nargs; arg_no++) { /* Skip arguments that is not suffixed with - * "__nullable". + * "__nullable or __ref". */ - if (!btf_param_match_suffix(btf, &stub_args[arg_no], - MAYBE_NULL_SUFFIX)) + is_nullable = btf_param_match_suffix(btf, &stub_args[arg_no], + MAYBE_NULL_SUFFIX); + is_refcounted = btf_param_match_suffix(btf, &stub_args[arg_no], + REFCOUNTED_SUFFIX); + + if (is_nullable) + suffix = MAYBE_NULL_SUFFIX; + else if (is_refcounted) + suffix = REFCOUNTED_SUFFIX; + else continue; /* Should be a pointer to struct */ @@ -236,7 +247,7 @@ static int prepare_arg_info(struct btf *btf, if (!pointed_type || !btf_type_is_struct(pointed_type)) { pr_warn("stub function %s has %s tagging to an unsupported type\n", - stub_fname, MAYBE_NULL_SUFFIX); + stub_fname, suffix); goto err_out; } @@ -254,11 +265,15 @@ static int prepare_arg_info(struct btf *btf, } /* Fill the information of the new argument */ - info->reg_type = - PTR_TRUSTED | PTR_TO_BTF_ID | PTR_MAYBE_NULL; info->btf_id = arg_btf_id; info->btf = btf; info->offset = offset; + if (is_nullable) { + info->reg_type = PTR_TRUSTED | PTR_TO_BTF_ID | PTR_MAYBE_NULL; + } else if (is_refcounted) { + info->reg_type = PTR_TRUSTED | PTR_TO_BTF_ID; + info->refcounted = true; + } info++; info_cnt++; -- cgit v1.2.3