bpf: Resolve symbols with ftrace_lookup_symbols for kprobe multi link

Using kallsyms_lookup_names function to speed up symbols lookup in
kprobe multi link attachment and replacing with it the current
kprobe_multi_resolve_syms function.

This speeds up bpftrace kprobe attachment:

# perf stat -r 5 -e cycles ./src/bpftrace -e 'kprobe:x* { } i:ms:1 { exit(); }'
...
6.5681 +- 0.0225 seconds time elapsed ( +- 0.34% )

After:

# perf stat -r 5 -e cycles ./src/bpftrace -e 'kprobe:x* { } i:ms:1 { exit(); }'
...
0.5661 +- 0.0275 seconds time elapsed ( +- 4.85% )

Acked-by: Andrii Nakryiko <[e-mail]>
Signed-off-by: Jiri Olsa <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

kernel/trace/bpf_trace.c

···
 	unsigned long entry_ip;
 };
 
+struct user_syms {
+	const char **syms;
+	char *buf;
+};
+
+static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32 cnt)
+{
+	unsigned long __user usymbol;
+	const char **syms = NULL;
+	char *buf = NULL, *p;
+	int err = -ENOMEM;
+	unsigned int i;
+
+	syms = kvmalloc(cnt * sizeof(*syms), GFP_KERNEL);
+	if (!syms)
+		goto error;
+
+	buf = kvmalloc(cnt * KSYM_NAME_LEN, GFP_KERNEL);
+	if (!buf)
+		goto error;
+
+	for (p = buf, i = 0; i < cnt; i++) {
+		if (__get_user(usymbol, usyms + i)) {
+			err = -EFAULT;
+			goto error;
+		}
+		err = strncpy_from_user(p, (const char __user *) usymbol, KSYM_NAME_LEN);
+		if (err == KSYM_NAME_LEN)
+			err = -E2BIG;
+		if (err < 0)
+			goto error;
+		syms[i] = p;
+		p += err + 1;
+	}
+
+	us->syms = syms;
+	us->buf = buf;
+	return 0;
+
+error:
+	if (err) {
+		kvfree(syms);
+		kvfree(buf);
+	}
+	return err;
+}
+
+static void free_user_syms(struct user_syms *us)
+{
+	kvfree(us->syms);
+	kvfree(us->buf);
+}
+
 static void bpf_kprobe_multi_link_release(struct bpf_link *link)
 {
 	struct bpf_kprobe_multi_link *kmulti_link;
···
 	kprobe_multi_link_prog_run(link, entry_ip, regs);
 }
 
-static int
-kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt,
-			  unsigned long *addrs)
+static int symbols_cmp(const void *a, const void *b)
 {
-	unsigned long addr, size;
-	const char __user **syms;
-	int err = -ENOMEM;
-	unsigned int i;
-	char *func;
+	const char **str_a = (const char **) a;
+	const char **str_b = (const char **) b;
 
-	size = cnt * sizeof(*syms);
-	syms = kvzalloc(size, GFP_KERNEL);
-	if (!syms)
-		return -ENOMEM;
-
-	func = kmalloc(KSYM_NAME_LEN, GFP_KERNEL);
-	if (!func)
-		goto error;
-
-	if (copy_from_user(syms, usyms, size)) {
-		err = -EFAULT;
-		goto error;
-	}
-
-	for (i = 0; i < cnt; i++) {
-		err = strncpy_from_user(func, syms[i], KSYM_NAME_LEN);
-		if (err == KSYM_NAME_LEN)
-			err = -E2BIG;
-		if (err < 0)
-			goto error;
-		err = -EINVAL;
-		addr = kallsyms_lookup_name(func);
-		if (!addr)
-			goto error;
-		if (!kallsyms_lookup_size_offset(addr, &size, NULL))
-			goto error;
-		addr = ftrace_location_range(addr, addr + size - 1);
-		if (!addr)
-			goto error;
-		addrs[i] = addr;
-	}
-
-	err = 0;
-error:
-	kvfree(syms);
-	kfree(func);
-	return err;
+	return strcmp(*str_a, *str_b);
 }
 
 int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
···
 			goto error;
 		}
 	} else {
-		err = kprobe_multi_resolve_syms(usyms, cnt, addrs);
+		struct user_syms us;
+
+		err = copy_user_syms(&us, usyms, cnt);
+		if (err)
+			goto error;
+
+		sort(us.syms, cnt, sizeof(*us.syms), symbols_cmp, NULL);
+		err = ftrace_lookup_symbols(us.syms, cnt, addrs);
+		free_user_syms(&us);
 		if (err)
 			goto error;
 	}