[PATCH bpf-next v6 10/17] bpf: Prepare architecture JIT support for stack arguments

[Yonghong Song <yonghong.song@linux.dev>]

Add bpf_jit_supports_stack_args() as a weak function defaulting to
false. Architectures that implement JIT support for stack arguments
override it to return true.

Reject BPF functions and kfuncs with more than 5 parameters at
verification time if the architecture does not support stack
arguments.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 include/linux/filter.h | 1 +
 kernel/bpf/btf.c       | 8 +++++++-
 kernel/bpf/core.c      | 5 +++++
 kernel/bpf/verifier.c  | 5 +++++
 4 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index b77d0b06db6e..911205dd670e 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1163,6 +1163,7 @@ bool bpf_jit_inlines_helper_call(s32 imm);
 bool bpf_jit_supports_subprog_tailcalls(void);
 bool bpf_jit_supports_percpu_insn(void);
 bool bpf_jit_supports_kfunc_call(void);
+bool bpf_jit_supports_stack_args(void);
 bool bpf_jit_supports_far_kfunc_call(void);
 bool bpf_jit_supports_exceptions(void);
 bool bpf_jit_supports_ptr_xchg(void);
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index c5f3aa05d5a3..3497e218c02d 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -7897,8 +7897,14 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 			tname, nargs, MAX_BPF_FUNC_REG_ARGS);
 		return -EINVAL;
 	}
-	if (nargs > MAX_BPF_FUNC_REG_ARGS)
+	if (nargs > MAX_BPF_FUNC_REG_ARGS) {
+		if (!bpf_jit_supports_stack_args()) {
+			bpf_log(log, "JIT does not support function %s() with %d args\n",
+				tname, nargs);
+			return -ENOTSUPP;
+		}
 		sub->incoming_stack_arg_depth = (nargs - MAX_BPF_FUNC_REG_ARGS) * BPF_REG_SIZE;
+	}
 
 	/* check that function is void or returns int, exception cb also requires this */
 	t = btf_type_by_id(btf, t->type);
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index ec8523e6e4eb..7522b3d7b267 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -3217,6 +3217,11 @@ bool __weak bpf_jit_supports_kfunc_call(void)
 	return false;
 }
 
+bool __weak bpf_jit_supports_stack_args(void)
+{
+	return false;
+}
+
 bool __weak bpf_jit_supports_far_kfunc_call(void)
 {
 	return false;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 78c9322870a5..e952ebcc2f8f 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12363,6 +12363,11 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 			MAX_BPF_FUNC_REG_ARGS);
 		return -EINVAL;
 	}
+	if (nargs > MAX_BPF_FUNC_REG_ARGS && !bpf_jit_supports_stack_args()) {
+		verbose(env, "JIT does not support kfunc %s() with %d args\n",
+			func_name, nargs);
+		return -ENOTSUPP;
+	}
 
 	/* Check that BTF function arguments match actual types that the
 	 * verifier sees.
-- 
2.52.0