Re: [PATCH] kprobes: x86_64: blacklist non-attachable interrupt functions

[Masami Hiramatsu]

Hi Andrea and Ingo,

Here is the patch what I meant. I just ran it on qemu-x86, and seemed working.
After introducing this patch, I will start adding arch_populate_kprobe_blacklist()
to some arches.

Thank you,

[RFC] kprobes: x86/kprobes: Blacklist symbols in arch-defined prohibited area

From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
 arch/x86/kernel/kprobes/core.c |   27 ++++++++++++++++++
 include/linux/kprobes.h        |    2 +
 kernel/kprobes.c               |   60 +++++++++++++++++++++++++++++++---------
 3 files changed, 75 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index c33b06f..52771e3 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -1034,6 +1034,33 @@ bool arch_within_kprobe_blacklist(unsigned long addr)
 		 addr < (unsigned long)__entry_text_end);
 }
 
+int __init arch_populate_kprobe_blacklist(void)
+{
+	unsigned long entry;
+	int ret = 0;
+
+	for (entry = (unsigned long)__kprobes_text_start;
+	     entry < (unsigned long)__kprobes_text_end;
+	     entry += ret) {
+		ret = kprobe_add_ksym_blacklist(entry);
+		if (ret < 0)
+			return ret;
+		if (ret == 0)	/* In case of alias symbol */
+			ret = 1;
+	}
+
+	for (entry = (unsigned long)__entry_text_start;
+	     entry < (unsigned long)__entry_text_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 arch_init_kprobes(void)
 {
 	return 0;
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index e909413..a68cbbe 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -242,10 +242,12 @@ 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);
 
 struct kprobe_insn_cache {
 	struct mutex mutex;
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 90e98e2..8b2eb62 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -2093,6 +2093,44 @@ 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 - offset;
+	ent->end_addr = entry - offset + size;
+	INIT_LIST_HEAD(&ent->list);
+	list_add_tail(&ent->list, &kprobe_blacklist);
+
+	return (int)size;
+}
+
+/* Add functions in arch defined probe-prohibited area */
+int __weak arch_populate_kprobe_blacklist(void)
+{
+	unsigned long entry;
+	int ret = 0;
+
+	for (entry = (unsigned long)__kprobes_text_start;
+	     entry < (unsigned long)__kprobes_text_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;
+}
+
 /*
  * Lookup and populate the kprobe_blacklist.
  *
@@ -2104,26 +2142,20 @@ 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;
+
+	return arch_populate_kprobe_blacklist();
 }
 
 /* Module notifier call back, checking kprobes on the module */