5 files changed, 35 insertions, 13 deletions
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index c915a6b54570..3697ad563899 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -200,4 +200,8 @@ extern const struct bpf_func_proto bpf_get_current_comm_proto;
 extern const struct bpf_func_proto bpf_skb_vlan_push_proto;
 extern const struct bpf_func_proto bpf_skb_vlan_pop_proto;
 
+/* Shared helpers among cBPF and eBPF. */
+void bpf_user_rnd_init_once(void);
+u64 bpf_user_rnd_u32(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);
+
 #endif /* _LINUX_BPF_H */
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index c8855c2a7a48..80864712d2c4 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -731,6 +731,32 @@ void bpf_prog_free(struct bpf_prog *fp)
 }
 EXPORT_SYMBOL_GPL(bpf_prog_free);
 
+/* RNG for unpriviledged user space with separated state from prandom_u32(). */
+static DEFINE_PER_CPU(struct rnd_state, bpf_user_rnd_state);
+
+void bpf_user_rnd_init_once(void)
+{
+	prandom_init_once(&bpf_user_rnd_state);
+}
+
+u64 bpf_user_rnd_u32(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+	/* Should someone ever have the rather unwise idea to use some
+	 * of the registers passed into this function, then note that
+	 * this function is called from native eBPF and classic-to-eBPF
+	 * transformations. Register assignments from both sides are
+	 * different, f.e. classic always sets fn(ctx, A, X) here.
+	 */
+	struct rnd_state *state;
+	u32 res;
+
+	state = &get_cpu_var(bpf_user_rnd_state);
+	res = prandom_u32_state(state);
+	put_cpu_var(state);
+
+	return res;
+}
+
 /* Weak definitions of helper functions in case we don't have bpf syscall. */
 const struct bpf_func_proto bpf_map_lookup_elem_proto __weak;
 const struct bpf_func_proto bpf_map_update_elem_proto __weak;
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 1447ec09421e..4504ca66118d 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -93,13 +93,8 @@ const struct bpf_func_proto bpf_map_delete_elem_proto = {
 	.arg2_type	= ARG_PTR_TO_MAP_KEY,
 };
 
-static u64 bpf_get_prandom_u32(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
-{
-	return prandom_u32();
-}
-
 const struct bpf_func_proto bpf_get_prandom_u32_proto = {
-	.func		= bpf_get_prandom_u32,
+	.func		= bpf_user_rnd_u32,
 	.gpl_only	= false,
 	.ret_type	= RET_INTEGER,
 };
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 5f35f420c12f..c868cafbc00c 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -404,6 +404,8 @@ static void fixup_bpf_calls(struct bpf_prog *prog)
 
 			if (insn->imm == BPF_FUNC_get_route_realm)
 				prog->dst_needed = 1;
+			if (insn->imm == BPF_FUNC_get_prandom_u32)
+				bpf_user_rnd_init_once();
 			if (insn->imm == BPF_FUNC_tail_call) {
 				/* mark bpf_tail_call as different opcode
 				 * to avoid conditional branch in
diff --git a/net/core/filter.c b/net/core/filter.c
index 8f4603c712cd..342e6c8fc415 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -149,12 +149,6 @@ static u64 __get_raw_cpu_id(u64 ctx, u64 a, u64 x, u64 r4, u64 r5)
 	return raw_smp_processor_id();
 }
 
-/* note that this only generates 32-bit random numbers */
-static u64 __get_random_u32(u64 ctx, u64 a, u64 x, u64 r4, u64 r5)
-{
-	return prandom_u32();
-}
-
 static u32 convert_skb_access(int skb_field, int dst_reg, int src_reg,
 			      struct bpf_insn *insn_buf)
 {
@@ -313,7 +307,8 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
 			*insn = BPF_EMIT_CALL(__get_raw_cpu_id);
 			break;
 		case SKF_AD_OFF + SKF_AD_RANDOM:
-			*insn = BPF_EMIT_CALL(__get_random_u32);
+			*insn = BPF_EMIT_CALL(bpf_user_rnd_u32);
+			bpf_user_rnd_init_once();
 			break;
 		}
 		break;