[PATCH bpf-next v2 11/23] 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 with more than 5 parameters at verification
time if the architecture does not support stack arguments.

Acked-by: Puranjay Mohan <puranjay@kernel.org>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 include/linux/filter.h | 1 +
 kernel/bpf/btf.c       | 8 +++++++-
 kernel/bpf/core.c      | 5 +++++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 918d9b34eac6..a515a9769078 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1184,6 +1184,7 @@ 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 ec3fb8c8f4ee..bf83b737d55c 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -7886,8 +7886,14 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 			MAX_BPF_FUNC_ARGS, tname, nargs);
 		return -EFAULT;
 	}
-	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->stack_arg_cnt = nargs - MAX_BPF_FUNC_REG_ARGS;
+	}
 
 	if (is_global && nargs > MAX_BPF_FUNC_REG_ARGS) {
 		bpf_log(log, "global function %s has %d > %d args, stack args not supported\n",
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 6f94b0ef3659..5d8932f5fb38 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;
-- 
2.53.0-Meta