[PATCH bpf-next v1 01/14] bpf: Split arena kfunc and struct_ops JIT capabilities

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

Arena pointer kfunc calls and struct_ops callbacks need different JIT
support. The former rebases BPF arena offsets before a kfunc call, while
the latter converts kernel pointers when an indirect trampoline builds a
callback context.

A single bpf_jit_supports_arena_args() hook forces an architecture to
implement both paths at once. That ties bpf_arena_alloc_pages()
conversion to struct_ops trampoline support and prevents the paths from
being enabled and reviewed independently.

Replace it with separate kfunc and struct_ops capability hooks. Make the
verifier query the hook for the path it is checking, and have x86-64 and
arm64 advertise both capabilities to preserve their current behavior.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 arch/arm64/net/bpf_jit_comp.c | 7 ++++++-
 arch/x86/net/bpf_jit_comp.c   | 7 ++++++-
 include/linux/filter.h        | 3 ++-
 kernel/bpf/core.c             | 7 ++++++-
 kernel/bpf/verifier.c         | 4 ++--
 5 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 3aa3ea0bc30b..eecaa0027a95 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -2398,7 +2398,12 @@ bool bpf_jit_supports_stack_args(void)
 	return true;
 }
 
-bool bpf_jit_supports_arena_args(void)
+bool bpf_jit_supports_arena_kfunc_args(void)
+{
+	return true;
+}
+
+bool bpf_jit_supports_arena_struct_ops_args(void)
 {
 	return true;
 }
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 48429fae0641..6e89f1c8738b 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -4174,7 +4174,12 @@ bool bpf_jit_supports_stack_args(void)
 	return true;
 }
 
-bool bpf_jit_supports_arena_args(void)
+bool bpf_jit_supports_arena_kfunc_args(void)
+{
+	return true;
+}
+
+bool bpf_jit_supports_arena_struct_ops_args(void)
 {
 	return true;
 }
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 6e746b0a0930..907d774fd355 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1239,7 +1239,8 @@ bool bpf_jit_supports_percpu_insn(void);
 bool bpf_jit_supports_kfunc_call(void);
 bool bpf_jit_supports_kfunc_ret_reg_pair(void);
 bool bpf_jit_supports_stack_args(void);
-bool bpf_jit_supports_arena_args(void);
+bool bpf_jit_supports_arena_kfunc_args(void);
+bool bpf_jit_supports_arena_struct_ops_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/core.c b/kernel/bpf/core.c
index 5db77d7915df..92b0a3bf27be 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -3297,7 +3297,12 @@ bool __weak bpf_jit_supports_stack_args(void)
 	return false;
 }
 
-bool __weak bpf_jit_supports_arena_args(void)
+bool __weak bpf_jit_supports_arena_kfunc_args(void)
+{
+	return false;
+}
+
+bool __weak bpf_jit_supports_arena_struct_ops_args(void)
 {
 	return false;
 }
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e036ae20bf6b..6402e94c2097 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12013,7 +12013,7 @@ get_kfunc_arg_type(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
 	else if (is_kfunc_arg_callback(env, meta->btf, &args[arg]))
 		arg_type = KF_ARG_PTR_TO_CALLBACK;
 	else if (is_kfunc_arg_arena(meta->btf, &args[arg])) {
-		if (!bpf_jit_supports_arena_args()) {
+		if (!bpf_jit_supports_arena_kfunc_args()) {
 			verbose(env, "JIT does not support kfunc %s() with arena pointer arguments\n",
 				meta->func_name);
 			return -ENOTSUPP;
@@ -19778,7 +19778,7 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
 		if (info->refcounted)
 			has_refcounted_arg = true;
 		if (base_type(info->reg_type) == PTR_TO_ARENA) {
-			if (!bpf_jit_supports_arena_args()) {
+			if (!bpf_jit_supports_arena_struct_ops_args()) {
 				verbose(env, "JIT does not support arena arguments\n");
 				return -ENOTSUPP;
 			}
-- 
2.53.0