bpf: add bpf_ktime_get_boot_ns()

On a device like a cellphone which is constantly suspending
and resuming CLOCK_MONOTONIC is not particularly useful for
keeping track of or reacting to external network events.
Instead you want to use CLOCK_BOOTTIME.

Hence add bpf_ktime_get_boot_ns() as a mirror of bpf_ktime_get_ns()
based around CLOCK_BOOTTIME instead of CLOCK_MONOTONIC.

Signed-off-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

3 files changed, 17 insertions, 0 deletions

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 0cc91805069a..6aa11de67315 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2156,6 +2156,7 @@ const struct bpf_func_proto bpf_get_prandom_u32_proto __weak;
 const struct bpf_func_proto bpf_get_smp_processor_id_proto __weak;
 const struct bpf_func_proto bpf_get_numa_node_id_proto __weak;
 const struct bpf_func_proto bpf_ktime_get_ns_proto __weak;
+const struct bpf_func_proto bpf_ktime_get_boot_ns_proto __weak;
 
 const struct bpf_func_proto bpf_get_current_pid_tgid_proto __weak;
 const struct bpf_func_proto bpf_get_current_uid_gid_proto __weak;
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 9a6b23387d02..5c0290e0696e 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -155,6 +155,18 @@ const struct bpf_func_proto bpf_ktime_get_ns_proto = {
 	.ret_type	= RET_INTEGER,
 };
 
+BPF_CALL_0(bpf_ktime_get_boot_ns)
+{
+	/* NMI safe access to clock boottime */
+	return ktime_get_boot_fast_ns();
+}
+
+const struct bpf_func_proto bpf_ktime_get_boot_ns_proto = {
+	.func		= bpf_ktime_get_boot_ns,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+};
+
 BPF_CALL_0(bpf_get_current_pid_tgid)
 {
 	struct task_struct *task = current;
@@ -615,6 +627,8 @@ bpf_base_func_proto(enum bpf_func_id func_id)
 		return &bpf_tail_call_proto;
 	case BPF_FUNC_ktime_get_ns:
 		return &bpf_ktime_get_ns_proto;
+	case BPF_FUNC_ktime_get_boot_ns:
+		return &bpf_ktime_get_boot_ns_proto;
 	default:
 		break;
 	}
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index ca1796747a77..e875c95d3ced 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -797,6 +797,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_map_peek_elem_proto;
 	case BPF_FUNC_ktime_get_ns:
 		return &bpf_ktime_get_ns_proto;
+	case BPF_FUNC_ktime_get_boot_ns:
+		return &bpf_ktime_get_boot_ns_proto;
 	case BPF_FUNC_tail_call:
 		return &bpf_tail_call_proto;
 	case BPF_FUNC_get_current_pid_tgid: