[bpf-next,1/2] bpf: x64: Add predicate for bpf2bpf with tailcalls support in JIT

Commit Message

Jakub Sitnicki June 17, 2022, 10:57 a.m. UTC

From: Tony Ambardar <[e-mail]>

The BPF core/verifier is hard-coded to permit mixing bpf2bpf and tail
calls for only x86-64. Change the logic to instead rely on a new weak
function 'bool bpf_jit_supports_subprog_tailcalls(void)', which a capable
JIT backend can override.

Update the x86-64 eBPF JIT to reflect this.

Signed-off-by: Tony Ambardar <[e-mail]>
[jakub: drop MIPS bits and tweak patch subject]
Signed-off-by: Jakub Sitnicki <[e-mail]>
---
 arch/x86/net/bpf_jit_comp.c | 6 ++++++
 include/linux/filter.h      | 1 +
 kernel/bpf/core.c           | 6 ++++++
 kernel/bpf/verifier.c       | 3 ++-
 4 files changed, 15 insertions(+), 1 deletion(-)

Patch

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index f298b18a9a3d..2c51ca9f7cec 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -2491,3 +2491,9 @@  void *bpf_arch_text_copy(void *dst, void *src, size_t len)
 		return ERR_PTR(-EINVAL);
 	return dst;
 }
+
+/* Indicate the JIT backend supports mixing bpf2bpf and tailcalls. */
+bool bpf_jit_supports_subprog_tailcalls(void)
+{
+	return true;
+}
diff --git a/include/linux/filter.h b/include/linux/filter.h
index d0cbb31b1b4d..4c1a8b247545 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -914,6 +914,7 @@  u64 __bpf_call_base(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);
 struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog);
 void bpf_jit_compile(struct bpf_prog *prog);
 bool bpf_jit_needs_zext(void);
+bool bpf_jit_supports_subprog_tailcalls(void);
 bool bpf_jit_supports_kfunc_call(void);
 bool bpf_helper_changes_pkt_data(void *func);
 
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index b5ffebcce6cc..f023cb399e3f 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2729,6 +2729,12 @@  bool __weak bpf_jit_needs_zext(void)
 	return false;
 }
 
+/* Return TRUE if the JIT backend supports mixing bpf2bpf and tailcalls. */
+bool __weak bpf_jit_supports_subprog_tailcalls(void)
+{
+	return false;
+}
+
 bool __weak bpf_jit_supports_kfunc_call(void)
 {
 	return false;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2859901ffbe3..f64d2598d7d8 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -6154,7 +6154,8 @@  static bool may_update_sockmap(struct bpf_verifier_env *env, int func_id)
 
 static bool allow_tail_call_in_subprogs(struct bpf_verifier_env *env)
 {
-	return env->prog->jit_requested && IS_ENABLED(CONFIG_X86_64);
+	return env->prog->jit_requested &&
+	       bpf_jit_supports_subprog_tailcalls();
 }
 
 static int check_map_func_compatibility(struct bpf_verifier_env *env,