[RFC PATCH 1/2] kprobes: Simplify kprobe blacklist management

[Naveen N. Rao]

Currently, the kprobe blacklist file in debugfs (usually
/sys/kernel/debug/kprobes/blacklist) does not capture all address
ranges that are blacklisted. For instance, functions annotated with
__kprobes (between __kprobes_text_start and __kprobes_text_end) are
blacklisted on all architectures. Certain architectures have additional
address ranges that are blacklisted.

These address ranges are currently prevented from being kprobe'd by
arch_within_kprobe_blacklist(). Instead, add the relevant address ranges
to the main kprobe blacklist allowing such address ranges to be
discovered by userspace.

With this patch, on powerpc64le, we see 2 additional entries at the end
of the blacklist:
root@ubuntu:/sys/kernel/debug# tail kprobes/blacklist
0xc00000000022d500-0xc00000000022d580	print_type_s64
0xc00000000022d480-0xc00000000022d500	print_type_s32
0xc00000000022d400-0xc00000000022d480	print_type_s16
0xc00000000022d380-0xc00000000022d400	print_type_s8
0xc00000000022d300-0xc00000000022d380	print_type_u64
0xc00000000022d280-0xc00000000022d300	print_type_u32
0xc00000000022d200-0xc00000000022d280	print_type_u16
0xc00000000022d180-0xc00000000022d200	print_type_u8
0xc0000000009ed778-0xc0000000009ed778	__irqentry_text_end
0xc000000000000000-0xc000000000008000	start_first_256B

__irqentry_text_end() happens to be at __kprobes_text_start and hence
figures there. Ditto with start_first_256B(). A subsequent patch helps
provide meaningful names for such address ranges.

Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
---
 arch/arm64/kernel/probes/kprobes.c | 31 +++++++++---------
 arch/powerpc/kernel/kprobes.c      | 10 +++---
 arch/x86/kernel/kprobes/core.c     | 10 +++---
 include/linux/kprobes.h            |  2 ++
 kernel/kprobes.c                   | 64 ++++++++++++++++++++++----------------
 5 files changed, 66 insertions(+), 51 deletions(-)

diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index c5c45942fb6e..7f453a71b5a8 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -535,24 +535,27 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 
 bool arch_within_kprobe_blacklist(unsigned long addr)
 {
-	if ((addr >= (unsigned long)__kprobes_text_start &&
-	    addr < (unsigned long)__kprobes_text_end) ||
-	    (addr >= (unsigned long)__entry_text_start &&
-	    addr < (unsigned long)__entry_text_end) ||
-	    (addr >= (unsigned long)__idmap_text_start &&
-	    addr < (unsigned long)__idmap_text_end) ||
-	    !!search_exception_tables(addr))
+	if (!!search_exception_tables(addr))
 		return true;
 
+	return false;
+}
+
+void __init arch_populate_kprobe_blacklist(void)
+{
+	insert_kprobe_blacklist((unsigned long)__kprobes_text_start,
+				(unsigned long)__kprobes_text_end);
+	insert_kprobe_blacklist((unsigned long)__entry_text_start,
+				(unsigned long)__entry_text_end);
+	insert_kprobe_blacklist((unsigned long)__idmap_text_start,
+				(unsigned long)__idmap_text_end);
+
 	if (!is_kernel_in_hyp_mode()) {
-		if ((addr >= (unsigned long)__hyp_text_start &&
-		    addr < (unsigned long)__hyp_text_end) ||
-		    (addr >= (unsigned long)__hyp_idmap_text_start &&
-		    addr < (unsigned long)__hyp_idmap_text_end))
-			return true;
+		insert_kprobe_blacklist((unsigned long)__hyp_text_start,
+					(unsigned long)__hyp_text_end);
+		insert_kprobe_blacklist((unsigned long)__hyp_idmap_text_start,
+					(unsigned long)__hyp_idmap_text_end);
 	}
-
-	return false;
 }
 
 void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 01addfb0ed0a..f707e42b3482 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -49,12 +49,12 @@ int is_current_kprobe_addr(unsigned long addr)
 	return (p && (unsigned long)p->addr == addr) ? 1 : 0;
 }
 
-bool arch_within_kprobe_blacklist(unsigned long addr)
+void __init arch_populate_kprobe_blacklist(void)
 {
-	return  (addr >= (unsigned long)__kprobes_text_start &&
-		 addr < (unsigned long)__kprobes_text_end) ||
-		(addr >= (unsigned long)_stext &&
-		 addr < (unsigned long)__head_end);
+	insert_kprobe_blacklist((unsigned long)__kprobes_text_start,
+				(unsigned long)__kprobes_text_end);
+	insert_kprobe_blacklist((unsigned long)_stext,
+				(unsigned long)__head_end);
 }
 
 kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 6b877807598b..4a5fc04b3e92 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -1141,12 +1141,12 @@ int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 }
 NOKPROBE_SYMBOL(longjmp_break_handler);
 
-bool arch_within_kprobe_blacklist(unsigned long addr)
+void __init arch_populate_kprobe_blacklist(void)
 {
-	return  (addr >= (unsigned long)__kprobes_text_start &&
-		 addr < (unsigned long)__kprobes_text_end) ||
-		(addr >= (unsigned long)__entry_text_start &&
-		 addr < (unsigned long)__entry_text_end);
+	insert_kprobe_blacklist((unsigned long)__kprobes_text_start,
+				(unsigned long)__kprobes_text_end);
+	insert_kprobe_blacklist((unsigned long)__entry_text_start,
+				(unsigned long)__entry_text_end);
 }
 
 int __init arch_init_kprobes(void)
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 541df0b5b815..6d931ea0604e 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -271,6 +271,8 @@ extern bool arch_function_offset_within_entry(unsigned long offset);
 extern bool function_offset_within_entry(kprobe_opcode_t *addr, const char *sym, unsigned long offset);
 
 extern bool within_kprobe_blacklist(unsigned long addr);
+extern void insert_kprobe_blacklist(unsigned long start, unsigned long end);
+extern void arch_populate_kprobe_blacklist(void);
 
 struct kprobe_insn_cache {
 	struct mutex mutex;
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index adfe3b4cfe05..8ddbee01ce01 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1364,12 +1364,7 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
 	return ret;
 }
 
-bool __weak arch_within_kprobe_blacklist(unsigned long addr)
-{
-	/* The __kprobes marked functions and entry code must not be probed */
-	return addr >= (unsigned long)__kprobes_text_start &&
-	       addr < (unsigned long)__kprobes_text_end;
-}
+bool __weak arch_within_kprobe_blacklist(unsigned long addr) { return false; }
 
 bool within_kprobe_blacklist(unsigned long addr)
 {
@@ -2125,12 +2120,40 @@ NOKPROBE_SYMBOL(dump_kprobe);
  * since a kprobe need not necessarily be at the beginning
  * of a function.
  */
-static int __init populate_kprobe_blacklist(unsigned long *start,
-					     unsigned long *end)
+
+/* Markers of _kprobe_blacklist section */
+extern unsigned long __start_kprobe_blacklist[];
+extern unsigned long __stop_kprobe_blacklist[];
+
+void __init insert_kprobe_blacklist(unsigned long start, unsigned long end)
 {
-	unsigned long *iter;
 	struct kprobe_blacklist_entry *ent;
+
+	ent = kmalloc(sizeof(*ent), GFP_KERNEL);
+	if (!ent) {
+		pr_err_once("kprobes: failed to populate blacklist: %d\n", -ENOMEM);
+		pr_err_once("Please take care of using kprobes.\n");
+	}
+
+	ent->start_addr = start;
+	ent->end_addr = end;
+	INIT_LIST_HEAD(&ent->list);
+	list_add_tail(&ent->list, &kprobe_blacklist);
+}
+
+void __weak __init arch_populate_kprobe_blacklist(void)
+{
+	/* The __kprobes marked functions and entry code must not be probed */
+	insert_kprobe_blacklist((unsigned long)__kprobes_text_start,
+				(unsigned long)__kprobes_text_end);
+}
+
+static void __init populate_kprobe_blacklist(void)
+{
+	unsigned long *iter;
 	unsigned long entry, offset = 0, size = 0;
+	unsigned long *start = __start_kprobe_blacklist;
+	unsigned long *end = __stop_kprobe_blacklist;
 
 	for (iter = start; iter < end; iter++) {
 		entry = arch_deref_entry_point((void *)*iter);
@@ -2142,15 +2165,11 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
 			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);
+		insert_kprobe_blacklist(entry, entry + size);
 	}
-	return 0;
+
+	/* Let architectures add their own entries as well */
+	arch_populate_kprobe_blacklist();
 }
 
 /* Module notifier call back, checking kprobes on the module */
@@ -2202,10 +2221,6 @@ static struct notifier_block kprobe_module_nb = {
 	.priority = 0
 };
 
-/* Markers of _kprobe_blacklist section */
-extern unsigned long __start_kprobe_blacklist[];
-extern unsigned long __stop_kprobe_blacklist[];
-
 static int __init init_kprobes(void)
 {
 	int i, err = 0;
@@ -2218,12 +2233,7 @@ static int __init init_kprobes(void)
 		raw_spin_lock_init(&(kretprobe_table_locks[i].lock));
 	}
 
-	err = populate_kprobe_blacklist(__start_kprobe_blacklist,
-					__stop_kprobe_blacklist);
-	if (err) {
-		pr_err("kprobes: failed to populate blacklist: %d\n", err);
-		pr_err("Please take care of using kprobes.\n");
-	}
+	populate_kprobe_blacklist();
 
 	if (kretprobe_blacklist_size) {
 		/* lookup the function address from its name */
-- 
2.13.1