linux-kernel - [PATCH v2 1/3] kprobes: Blacklist symbols in arch-defined prohibited area

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Date:   Mon, 17 Dec 2018 17:20:55 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Ingo Molnar <mingo@...hat.com>,
        Andrea Righi <righi.andrea@...il.com>
Cc:     "Naveen N . Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Yonghong Song <yhs@...com>, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/3] kprobes: Blacklist symbols in arch-defined prohibited area

Blacklist symbols in arch-defined probe-prohibited areas.
With this change, user can see all symbols which are prohibited
to probe in debugfs.

All archtectures which have custom prohibit areas should define
its own arch_populate_kprobe_blacklist() function, but unless that,
all symbols marked __kprobes are blacklisted.

Reported-by: Andrea Righi <righi.andrea@...il.com>
Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 Changes in v2:
  - Add area based blacklist adding helper function
  - Blacklist __kprobes_text symbols by default
  - Add __init to default function
---
 include/linux/kprobes.h |    3 ++
 kernel/kprobes.c        |   67 +++++++++++++++++++++++++++++++++++++----------
 2 files changed, 56 insertions(+), 14 deletions(-)

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index e64b26c81c2f..e07e91daaacc 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -242,10 +242,13 @@ extern int arch_init_kprobes(void);
 extern void show_registers(struct pt_regs *regs);
 extern void kprobes_inc_nmissed_count(struct kprobe *p);
 extern bool arch_within_kprobe_blacklist(unsigned long addr);
+extern int arch_populate_kprobe_blacklist(void);
 extern bool arch_kprobe_on_func_entry(unsigned long offset);
 extern bool kprobe_on_func_entry(kprobe_opcode_t *addr, const char *sym, unsigned long offset);
 
 extern bool within_kprobe_blacklist(unsigned long addr);
+extern int kprobe_add_ksym_blacklist(unsigned long entry);
+extern int kprobe_add_area_blacklist(unsigned long start, unsigned long end);
 
 struct kprobe_insn_cache {
 	struct mutex mutex;
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 08e31d863191..f4ddfdd2d07e 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -2093,6 +2093,47 @@ void dump_kprobe(struct kprobe *kp)
 }
 NOKPROBE_SYMBOL(dump_kprobe);
 
+int kprobe_add_ksym_blacklist(unsigned long entry)
+{
+	struct kprobe_blacklist_entry *ent;
+	unsigned long offset = 0, size = 0;
+
+	if (!kernel_text_address(entry) ||
+	    !kallsyms_lookup_size_offset(entry, &size, &offset))
+		return -EINVAL;
+
+	ent = kmalloc(sizeof(*ent), GFP_KERNEL);
+	if (!ent)
+		return -ENOMEM;
+	ent->start_addr = entry;
+	ent->end_addr = entry + size;
+	INIT_LIST_HEAD(&ent->list);
+	list_add_tail(&ent->list, &kprobe_blacklist);
+
+	return (int)size;
+}
+
+/* Add all symbols in given area into kprobe blacklist */
+int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
+{
+	unsigned long entry;
+	int ret = 0;
+
+	for (entry = start; entry < end; entry += ret) {
+		ret = kprobe_add_ksym_blacklist(entry);
+		if (ret < 0)
+			return ret;
+		if (ret == 0)	/* In case of alias symbol */
+			ret = 1;
+	}
+	return 0;
+}
+
+int __init __weak arch_populate_kprobe_blacklist(void)
+{
+	return 0;
+}
+
 /*
  * Lookup and populate the kprobe_blacklist.
  *
@@ -2104,26 +2145,24 @@ NOKPROBE_SYMBOL(dump_kprobe);
 static int __init populate_kprobe_blacklist(unsigned long *start,
 					     unsigned long *end)
 {
+	unsigned long entry;
 	unsigned long *iter;
-	struct kprobe_blacklist_entry *ent;
-	unsigned long entry, offset = 0, size = 0;
+	int ret;
 
 	for (iter = start; iter < end; iter++) {
 		entry = arch_deref_entry_point((void *)*iter);
-
-		if (!kernel_text_address(entry) ||
-		    !kallsyms_lookup_size_offset(entry, &size, &offset))
+		ret = kprobe_add_ksym_blacklist(entry);
+		if (ret == -EINVAL)
 			continue;
-
-		ent = kmalloc(sizeof(*ent), GFP_KERNEL);
-		if (!ent)
-			return -ENOMEM;
-		ent->start_addr = entry;
-		ent->end_addr = entry + size;
-		INIT_LIST_HEAD(&ent->list);
-		list_add_tail(&ent->list, &kprobe_blacklist);
+		if (ret < 0)
+			return ret;
 	}
-	return 0;
+
+	/* Symbols in __kprobes_text are blacklisted */
+	ret = kprobe_add_area_blacklist((unsigned long)__kprobes_text_start,
+					(unsigned long)__kprobes_text_end);
+
+	return ret ? : arch_populate_kprobe_blacklist();
 }
 
 /* Module notifier call back, checking kprobes on the module */