[bpf-next v6 3/5] bpf: Add helper to detect indirect jump targets

[Xu Kuohai]

From: Xu Kuohai <xukuohai@xxxxxxxxxx>

Introduce helper bpf_insn_is_indirect_target to check whether a BPF
instruction is an indirect jump target.

Since the verifier knows which instructions are indirect jump targets,
add a new flag indirect_target to struct bpf_insn_aux_data to mark
them. The verifier sets this flag when verifing an indirect jump target
instruction, and the helper checks it to determine whether an
instruction is an indirect jump target.

Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
---
 include/linux/bpf.h          | 2 ++
 include/linux/bpf_verifier.h | 9 +++++----
 kernel/bpf/core.c            | 9 +++++++++
 kernel/bpf/verifier.c        | 7 +++++++
 4 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 05b34a6355b0..90760e250865 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1541,6 +1541,8 @@ bool bpf_has_frame_pointer(unsigned long ip);
 int bpf_jit_charge_modmem(u32 size);
 void bpf_jit_uncharge_modmem(u32 size);
 bool bpf_prog_has_trampoline(const struct bpf_prog *prog);
+bool bpf_insn_is_indirect_target(const struct bpf_verifier_env *env, const struct bpf_prog *prog,
+				 int insn_idx);
 #else
 static inline int bpf_trampoline_link_prog(struct bpf_tramp_link *link,
 					   struct bpf_trampoline *tr,
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 090aa26d1c98..6431b94746cf 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -578,16 +578,17 @@ struct bpf_insn_aux_data {
 
 	/* below fields are initialized once */
 	unsigned int orig_idx; /* original instruction index */
-	bool jmp_point;
-	bool prune_point;
+	u32 jmp_point:1;
+	u32 prune_point:1;
 	/* ensure we check state equivalence and save state checkpoint and
 	 * this instruction, regardless of any heuristics
 	 */
-	bool force_checkpoint;
+	u32 force_checkpoint:1;
 	/* true if instruction is a call to a helper function that
 	 * accepts callback function as a parameter.
 	 */
-	bool calls_callback;
+	u32 calls_callback:1;
+	u32 indirect_target:1; /* if it is an indirect jump target */
 	/*
 	 * CFG strongly connected component this instruction belongs to,
 	 * zero if it is a singleton SCC.
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 741e09b8a2be..31a57de520af 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1290,6 +1290,15 @@ const char *bpf_jit_get_prog_name(struct bpf_prog *prog)
 		return prog->aux->ksym.name;
 	return prog->aux->name;
 }
+
+bool bpf_insn_is_indirect_target(const struct bpf_verifier_env *env, const struct bpf_prog *prog,
+				 int insn_idx)
+{
+	if (!env)
+		return false;
+	insn_idx += prog->aux->subprog_start;
+	return env->insn_aux_data[insn_idx].indirect_target;
+}
 #endif /* CONFIG_BPF_JIT */
 
 /* Base function for offset calculation. Needs to go into .text section,
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 06202ba53aec..13f34f2dd2b6 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3998,6 +3998,11 @@ static bool is_jmp_point(struct bpf_verifier_env *env, int insn_idx)
 	return env->insn_aux_data[insn_idx].jmp_point;
 }
 
+static void mark_indirect_target(struct bpf_verifier_env *env, int idx)
+{
+	env->insn_aux_data[idx].indirect_target = true;
+}
+
 #define LR_FRAMENO_BITS	3
 #define LR_SPI_BITS	6
 #define LR_ENTRY_BITS	(LR_SPI_BITS + LR_FRAMENO_BITS + 1)
@@ -21051,12 +21056,14 @@ static int check_indirect_jump(struct bpf_verifier_env *env, struct bpf_insn *in
 	}
 
 	for (i = 0; i < n - 1; i++) {
+		mark_indirect_target(env, env->gotox_tmp_buf->items[i]);
 		other_branch = push_stack(env, env->gotox_tmp_buf->items[i],
 					  env->insn_idx, env->cur_state->speculative);
 		if (IS_ERR(other_branch))
 			return PTR_ERR(other_branch);
 	}
 	env->insn_idx = env->gotox_tmp_buf->items[n-1];
+	mark_indirect_target(env, env->insn_idx);
 	return 0;
 }
 
-- 
2.47.3