bpf: Add bpf_copy_from_user_task() helper

This adds a helper for bpf programs to read the memory of other
tasks.

As an example use case at Meta, we are using a bpf task iterator program
and this new helper to print C++ async stack traces for all threads of
a given process.

Signed-off-by: Kenny Yu <kennyyu@fb.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20220124185403.468466-3-kennyyu@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 36 insertions, 0 deletions

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 01cfdf40c838..ed2780b76cc1 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -16,6 +16,7 @@
 #include <linux/pid_namespace.h>
 #include <linux/proc_ns.h>
 #include <linux/security.h>
+#include <linux/btf_ids.h>
 
 #include "../../lib/kstrtox.h"
 
@@ -671,6 +672,39 @@ const struct bpf_func_proto bpf_copy_from_user_proto = {
 	.arg3_type	= ARG_ANYTHING,
 };
 
+BPF_CALL_5(bpf_copy_from_user_task, void *, dst, u32, size,
+	   const void __user *, user_ptr, struct task_struct *, tsk, u64, flags)
+{
+	int ret;
+
+	/* flags is not used yet */
+	if (unlikely(flags))
+		return -EINVAL;
+
+	if (unlikely(!size))
+		return 0;
+
+	ret = access_process_vm(tsk, (unsigned long)user_ptr, dst, size, 0);
+	if (ret == size)
+		return 0;
+
+	memset(dst, 0, size);
+	/* Return -EFAULT for partial read */
+	return ret < 0 ? ret : -EFAULT;
+}
+
+const struct bpf_func_proto bpf_copy_from_user_task_proto = {
+	.func		= bpf_copy_from_user_task,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_UNINIT_MEM,
+	.arg2_type	= ARG_CONST_SIZE_OR_ZERO,
+	.arg3_type	= ARG_ANYTHING,
+	.arg4_type	= ARG_PTR_TO_BTF_ID,
+	.arg4_btf_id	= &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
+	.arg5_type	= ARG_ANYTHING
+};
+
 BPF_CALL_2(bpf_per_cpu_ptr, const void *, ptr, u32, cpu)
 {
 	if (cpu >= nr_cpu_ids)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 06a9e220069e..a2024ba32a20 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1235,6 +1235,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_get_task_stack_proto;
 	case BPF_FUNC_copy_from_user:
 		return prog->aux->sleepable ? &bpf_copy_from_user_proto : NULL;
+	case BPF_FUNC_copy_from_user_task:
+		return prog->aux->sleepable ? &bpf_copy_from_user_task_proto : NULL;
 	case BPF_FUNC_snprintf_btf:
 		return &bpf_snprintf_btf_proto;
 	case BPF_FUNC_per_cpu_ptr: