bpf: Add bpf_line_info support

This patch adds bpf_line_info support.

It accepts an array of bpf_line_info objects during BPF_PROG_LOAD.
The "line_info", "line_info_cnt" and "line_info_rec_size" are added
to the "union bpf_attr".  The "line_info_rec_size" makes
bpf_line_info extensible in the future.

The new "check_btf_line()" ensures the userspace line_info is valid
for the kernel to use.

When the verifier is translating/patching the bpf_prog (through
"bpf_patch_insn_single()"), the line_infos' insn_off is also
adjusted by the newly added "bpf_adj_linfo()".

If the bpf_prog is jited, this patch also provides the jited addrs (in
aux->jited_linfo) for the corresponding line_info.insn_off.
"bpf_prog_fill_jited_linfo()" is added to fill the aux->jited_linfo.
It is currently called by the x86 jit.  Other jits can also use
"bpf_prog_fill_jited_linfo()" and it will be done in the followup patches.
In the future, if it deemed necessary, a particular jit could also provide
its own "bpf_prog_fill_jited_linfo()" implementation.

A few "*line_info*" fields are added to the bpf_prog_info such
that the user can get the xlated line_info back (i.e. the line_info
with its insn_off reflecting the translated prog).  The jited_line_info
is available if the prog is jited.  It is an array of __u64.
If the prog is not jited, jited_line_info_cnt is 0.

The verifier's verbose log with line_info will be done in
a follow up patch.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/core.c

@@ -105,6 +105,91 @@ struct bpf_prog *bpf_prog_alloc(unsigned int size, gfp_t gfp_extra_flags)
 }
 EXPORT_SYMBOL_GPL(bpf_prog_alloc);
 
+int bpf_prog_alloc_jited_linfo(struct bpf_prog *prog)
+{
+	if (!prog->aux->nr_linfo || !prog->jit_requested)
+		return 0;
+
+	prog->aux->jited_linfo = kcalloc(prog->aux->nr_linfo,
+					 sizeof(*prog->aux->jited_linfo),
+					 GFP_KERNEL | __GFP_NOWARN);
+	if (!prog->aux->jited_linfo)
+		return -ENOMEM;
+
+	return 0;
+}
+
+void bpf_prog_free_jited_linfo(struct bpf_prog *prog)
+{
+	kfree(prog->aux->jited_linfo);
+	prog->aux->jited_linfo = NULL;
+}
+
+void bpf_prog_free_unused_jited_linfo(struct bpf_prog *prog)
+{
+	if (prog->aux->jited_linfo && !prog->aux->jited_linfo[0])
+		bpf_prog_free_jited_linfo(prog);
+}
+
+/* The jit engine is responsible to provide an array
+ * for insn_off to the jited_off mapping (insn_to_jit_off).
+ *
+ * The idx to this array is the insn_off.  Hence, the insn_off
+ * here is relative to the prog itself instead of the main prog.
+ * This array has one entry for each xlated bpf insn.
+ *
+ * jited_off is the byte off to the last byte of the jited insn.
+ *
+ * Hence, with
+ * insn_start:
+ *      The first bpf insn off of the prog.  The insn off
+ *      here is relative to the main prog.
+ *      e.g. if prog is a subprog, insn_start > 0
+ * linfo_idx:
+ *      The prog's idx to prog->aux->linfo and jited_linfo
+ *
+ * jited_linfo[linfo_idx] = prog->bpf_func
+ *
+ * For i > linfo_idx,
+ *
+ * jited_linfo[i] = prog->bpf_func +
+ *	insn_to_jit_off[linfo[i].insn_off - insn_start - 1]
+ */
+void bpf_prog_fill_jited_linfo(struct bpf_prog *prog,
+			       const u32 *insn_to_jit_off)
+{
+	u32 linfo_idx, insn_start, insn_end, nr_linfo, i;
+	const struct bpf_line_info *linfo;
+	void **jited_linfo;
+
+	if (!prog->aux->jited_linfo)
+		/* Userspace did not provide linfo */
+		return;
+
+	linfo_idx = prog->aux->linfo_idx;
+	linfo = &prog->aux->linfo[linfo_idx];
+	insn_start = linfo[0].insn_off;
+	insn_end = insn_start + prog->len;
+
+	jited_linfo = &prog->aux->jited_linfo[linfo_idx];
+	jited_linfo[0] = prog->bpf_func;
+
+	nr_linfo = prog->aux->nr_linfo - linfo_idx;
+
+	for (i = 1; i < nr_linfo && linfo[i].insn_off < insn_end; i++)
+		/* The verifier ensures that linfo[i].insn_off is
+		 * strictly increasing
+		 */
+		jited_linfo[i] = prog->bpf_func +
+			insn_to_jit_off[linfo[i].insn_off - insn_start - 1];
+}
+
+void bpf_prog_free_linfo(struct bpf_prog *prog)
+{
+	bpf_prog_free_jited_linfo(prog);
+	kvfree(prog->aux->linfo);
+}
+
 struct bpf_prog *bpf_prog_realloc(struct bpf_prog *fp_old, unsigned int size,
 				  gfp_t gfp_extra_flags)
 {
@@ -294,6 +379,26 @@ static int bpf_adj_branches(struct bpf_prog *prog, u32 pos, u32 delta,
 	return ret;
 }
 
+static void bpf_adj_linfo(struct bpf_prog *prog, u32 off, u32 delta)
+{
+	struct bpf_line_info *linfo;
+	u32 i, nr_linfo;
+
+	nr_linfo = prog->aux->nr_linfo;
+	if (!nr_linfo || !delta)
+		return;
+
+	linfo = prog->aux->linfo;
+
+	for (i = 0; i < nr_linfo; i++)
+		if (off < linfo[i].insn_off)
+			break;
+
+	/* Push all off < linfo[i].insn_off by delta */
+	for (; i < nr_linfo; i++)
+		linfo[i].insn_off += delta;
+}
+
 struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
 				       const struct bpf_insn *patch, u32 len)
 {
@@ -349,6 +454,8 @@ struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
 	 */
 	BUG_ON(bpf_adj_branches(prog_adj, off, insn_delta, false));
 
+	bpf_adj_linfo(prog_adj, off, insn_delta);
+
 	return prog_adj;
 }
 
@@ -1591,13 +1698,20 @@ struct bpf_prog *bpf_prog_select_runtime(struct bpf_prog *fp, int *err)
 	 * be JITed, but falls back to the interpreter.
 	 */
 	if (!bpf_prog_is_dev_bound(fp->aux)) {
+		*err = bpf_prog_alloc_jited_linfo(fp);
+		if (*err)
+			return fp;
+
 		fp = bpf_int_jit_compile(fp);
-#ifdef CONFIG_BPF_JIT_ALWAYS_ON
 		if (!fp->jited) {
+			bpf_prog_free_jited_linfo(fp);
+#ifdef CONFIG_BPF_JIT_ALWAYS_ON
 			*err = -ENOTSUPP;
 			return fp;
-		}
 #endif
+		} else {
+			bpf_prog_free_unused_jited_linfo(fp);
+		}
 	} else {
 		*err = bpf_prog_offload_compile(fp);
 		if (*err)