[PATCH bpf-next 06/12] bpf: Force JIT for programs using the R0:R2 register pair

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

The R0:R2 return convention introduced in this series is only implemented
in the JIT. The BPF interpreter has no notion of a second return register,
so a program relying on the R0:R2 convention would compute wrong results
under the interpreter. Force the JIT when bpf_prog_aux->ret_reg_pair is
set.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 include/linux/bpf.h   |  1 +
 kernel/bpf/core.c     |  2 +-
 kernel/bpf/verifier.c | 13 +++++++++++--
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index c1a98fa36738..10966aba69a2 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1780,6 +1780,7 @@ struct bpf_prog_aux {
 	bool changes_pkt_data;
 	bool might_sleep;
 	bool kprobe_write_ctx;
+	bool ret_reg_pair;
 	struct {
 		s32 keyring_serial;
 		u8 keyring_type;
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 73dc3ee879de..819a97d25173 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2676,7 +2676,7 @@ struct bpf_prog *__bpf_prog_select_runtime(struct bpf_verifier_env *env, struct
 		goto finalize;
 
 	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) ||
-	    bpf_prog_has_kfunc_call(fp))
+	    bpf_prog_has_kfunc_call(fp) || fp->aux->ret_reg_pair)
 		jit_needed = true;
 
 	if (!bpf_prog_select_interpreter(fp))
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index fcbf532159a5..ca8b2f436c20 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -453,6 +453,15 @@ bool bpf_ret_reg_pair(struct bpf_verifier_env *env, int subprog)
 	return false;
 }
 
+static bool bpf_ret_reg_pair_mark(struct bpf_verifier_env *env, int subprog)
+{
+	if (!bpf_ret_reg_pair(env, subprog))
+		return false;
+
+	env->prog->aux->ret_reg_pair = true;
+	return true;
+}
+
 static const char *subprog_name(const struct bpf_verifier_env *env, int subprog)
 {
 	struct bpf_func_info *info;
@@ -9877,7 +9886,7 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
 	} else {
 		/* return to the caller whatever r0 had in the callee */
 		caller->regs[BPF_REG_0] = *r0;
-		if (bpf_ret_reg_pair(env, callee->subprogno)) {
+		if (bpf_ret_reg_pair_mark(env, callee->subprogno)) {
 			if (callee->regs[BPF_REG_2].type == PTR_TO_STACK) {
 				verbose(env, "cannot return stack pointer to the caller\n");
 				return -EINVAL;
@@ -16806,7 +16815,7 @@ static int check_global_subprog_return_code(struct bpf_verifier_env *env)
 	if (err)
 		return err;
 
-	if (!bpf_ret_reg_pair(env, subprog))
+	if (!bpf_ret_reg_pair_mark(env, subprog))
 		return 0;
 
 	return check_global_ret_scalar_reg(env, BPF_REG_2);
-- 
2.53.0-Meta