[PATCH -tip v4 2/6] kprobes: Introduce NOKPROBE_SYMBOL() macro forblacklist

From: Masami Hiramatsu
Date: Tue Dec 03 2013 - 20:34:41 EST

Introduce NOKPROBE_SYMBOL() macro which builds a kprobe
blacklist in build time. The usage of this macro is similar
to the EXPORT_SYMBOL, put the NOKPROBE_SYMBOL(function); just
after the function definition.

When CONFIG_KPROBES=y, the macro stores the given function
address in the "_kprobe_blacklist" section.

Since the data structures are not fully initialized by the
macro (because there is no "size" information), those
are re-initialized at boot time by using kallsyms.

Changes from previous version:
- Rename kprobe_blackpoint to kprobe_blacklist_entry and
simplify it.
- Just stores the address of given function instead of
defining a data structure in NOKPROBE_SYMBOL().
- Add _ASM_NOKPROBE macro support for x86.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Cc: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Rob Landley <rob@xxxxxxxxxxx>
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Cc: Chris Wright <chrisw@xxxxxxxxxxxx>
Cc: Alok Kataria <akataria@xxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
Documentation/kprobes.txt | 16 ++++++
arch/x86/include/asm/asm.h | 7 +++
arch/x86/kernel/paravirt.c | 4 +
include/asm-generic/vmlinux.lds.h | 9 +++
include/linux/kprobes.h | 20 ++++++-
kernel/kprobes.c | 100 +++++++++++++++++++------------------
kernel/sched/core.c | 1
7 files changed, 105 insertions(+), 52 deletions(-)

diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt
index 0cfb00f..7062631 100644
--- a/Documentation/kprobes.txt
+++ b/Documentation/kprobes.txt
@@ -22,8 +22,9 @@ Appendix B: The kprobes sysctl interface

Kprobes enables you to dynamically break into any kernel routine and
collect debugging and performance information non-disruptively. You
-can trap at almost any kernel code address, specifying a handler
+can trap at almost any kernel code address(*), specifying a handler
routine to be invoked when the breakpoint is hit.
+(*: at some part of kernel code can not be trapped, see 1.5 Blacklist)

There are currently three types of probes: kprobes, jprobes, and
kretprobes (also called return probes). A kprobe can be inserted
@@ -273,6 +274,19 @@ using one of the following techniques:
or
- Execute 'sysctl -w debug.kprobes_optimization=n'

+1.5 Blacklist
+
+Kprobes can probe almost of the kernel except itself. This means
+that there are some functions where kprobes cannot probe. Probing
+(trapping) such functions can cause recursive trap (e.g. double
+fault) or at least the nested probe handler never be called.
+Kprobes manages such functions as a blacklist.
+If you want to add a function into the blacklist, you just need
+to (1) include linux/kprobes.h and (2) use NOKPROBE_SYMBOL() macro
+to specify a blacklisted function.
+Kprobes checks given probe address with the blacklist and reject
+registering if the given address is in the blacklist.
+
2. Architectures Supported

Kprobes, jprobes, and return probes are implemented on the following
diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index 4582e8e..7730c1c 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -57,6 +57,12 @@
.long (from) - . ; \
.long (to) - . + 0x7ffffff0 ; \
.popsection
+
+# define _ASM_NOKPROBE(entry) \
+ .pushsection "_kprobe_blacklist","aw" ; \
+ _ASM_ALIGN ; \
+ _ASM_PTR (entry); \
+ .popsection
#else
# define _ASM_EXTABLE(from,to) \
" .pushsection \"__ex_table\",\"a\"\n" \
@@ -71,6 +77,7 @@
" .long (" #from ") - .\n" \
" .long (" #to ") - . + 0x7ffffff0\n" \
" .popsection\n"
+/* For C file, we already have NOKPROBE_SYMBOL macro */
#endif

#endif /* _ASM_X86_ASM_H */
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 1b10af8..4c785fd 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -23,6 +23,7 @@
#include <linux/efi.h>
#include <linux/bcd.h>
#include <linux/highmem.h>
+#include <linux/kprobes.h>

#include <asm/bug.h>
#include <asm/paravirt.h>
@@ -389,6 +390,9 @@ __visible struct pv_cpu_ops pv_cpu_ops = {
.end_context_switch = paravirt_nop,
};

+/* At this point, native_get_debugreg has real function entry */
+NOKPROBE_SYMBOL(native_get_debugreg);
+
struct pv_apic_ops pv_apic_ops = {
#ifdef CONFIG_X86_LOCAL_APIC
.startup_ipi_hook = paravirt_nop,
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index bc2121f..81d07d5 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -109,6 +109,14 @@
#define BRANCH_PROFILE()
#endif

+#ifdef CONFIG_KPROBES
+#define KPROBE_BLACKLIST() VMLINUX_SYMBOL(__start_kprobe_blacklist) = .; \
+ *(_kprobe_blacklist) \
+ VMLINUX_SYMBOL(__stop_kprobe_blacklist) = .;
+#else
+#define KPROBE_BLACKLIST()
+#endif
+
#ifdef CONFIG_EVENT_TRACING
#define FTRACE_EVENTS() . = ALIGN(8); \
VMLINUX_SYMBOL(__start_ftrace_events) = .; \
@@ -488,6 +496,7 @@
*(.init.rodata) \
FTRACE_EVENTS() \
TRACE_SYSCALLS() \
+ KPROBE_BLACKLIST() \
MEM_DISCARD(init.rodata) \
CLK_OF_TABLES() \
CLKSRC_OF_TABLES() \
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index cdf9251..e059507 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -205,10 +205,10 @@ struct kretprobe_blackpoint {
void *addr;
};

-struct kprobe_blackpoint {
- const char *name;
+struct kprobe_blacklist_entry {
+ struct list_head list;
unsigned long start_addr;
- unsigned long range;
+ unsigned long end_addr;
};

#ifdef CONFIG_KPROBES
@@ -477,4 +477,18 @@ static inline int enable_jprobe(struct jprobe *jp)
return enable_kprobe(&jp->kp);
}

+#ifdef CONFIG_KPROBES
+/*
+ * Blacklist ganerating macro. Specify functions which is not probed
+ * by using this macro.
+ */
+#define __NOKPROBE_SYMBOL(fname) \
+static unsigned long __used \
+ __attribute__((section("_kprobe_blacklist"))) \
+ _kbl_addr_##fname = (unsigned long)fname;
+#define NOKPROBE_SYMBOL(fname) __NOKPROBE_SYMBOL(fname)
+#else
+#define NOKPROBE_SYMBOL(fname)
+#endif
+
#endif /* _LINUX_KPROBES_H */
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index c6772b9..43ef40b 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -86,18 +86,8 @@ static raw_spinlock_t *kretprobe_table_lock_ptr(unsigned long hash)
return &(kretprobe_table_locks[hash].lock);
}

-/*
- * Normally, functions that we'd want to prohibit kprobes in, are marked
- * __kprobes. But, there are cases where such functions already belong to
- * a different section (__sched for preempt_schedule)
- *
- * For such cases, we now have a blacklist
- */
-static struct kprobe_blackpoint kprobe_blacklist[] = {
- {"preempt_schedule",},
- {"native_get_debugreg",},
- {NULL} /* Terminator */
-};
+/* Blacklist -- list of struct kprobe_blacklist_entry */
+static LIST_HEAD(kprobe_blacklist);

#ifdef __ARCH_WANT_KPROBES_INSN_SLOT
/*
@@ -1328,24 +1318,22 @@ bool __weak arch_within_kprobe_blacklist(unsigned long addr)
addr < (unsigned long)__kprobes_text_end);
}

-static int __kprobes in_kprobes_functions(unsigned long addr)
+static bool __kprobes within_kprobe_blacklist(unsigned long addr)
{
- struct kprobe_blackpoint *kb;
+ struct kprobe_blacklist_entry *ent;

if (arch_within_kprobe_blacklist(addr))
- return -EINVAL;
+ return true;
/*
* If there exists a kprobe_blacklist, verify and
* fail any probe registration in the prohibited area
*/
- for (kb = kprobe_blacklist; kb->name != NULL; kb++) {
- if (kb->start_addr) {
- if (addr >= kb->start_addr &&
- addr < (kb->start_addr + kb->range))
- return -EINVAL;
- }
+ list_for_each_entry(ent, &kprobe_blacklist, list) {
+ if (addr >= ent->start_addr && addr < ent->end_addr)
+ return true;
}
- return 0;
+
+ return false;
}

/*
@@ -1436,7 +1424,7 @@ static __kprobes int check_kprobe_address_safe(struct kprobe *p,

/* Ensure it is not in reserved area nor out of text */
if (!kernel_text_address((unsigned long) p->addr) ||
- in_kprobes_functions((unsigned long) p->addr) ||
+ within_kprobe_blacklist((unsigned long) p->addr) ||
jump_label_text_reserved(p->addr, p->addr)) {
ret = -EINVAL;
goto out;
@@ -2022,6 +2010,38 @@ void __kprobes dump_kprobe(struct kprobe *kp)
kp->symbol_name, kp->addr, kp->offset);
}

+/*
+ * Lookup and populate the kprobe_blacklist.
+ *
+ * Unlike the kretprobe blacklist, we'll need to determine
+ * the range of addresses that belong to the said functions,
+ * 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)
+{
+ unsigned long *iter;
+ struct kprobe_blacklist_entry *ent;
+ unsigned long offset = 0, size = 0;
+
+ for (iter = start; iter < end; iter++) {
+ if (!kallsyms_lookup_size_offset(*iter, &size, &offset)) {
+ pr_err("Failed to find blacklist %p\n", (void *)*iter);
+ continue;
+ }
+
+ ent = kmalloc(sizeof(*ent), GFP_KERNEL);
+ if (!ent)
+ return -ENOMEM;
+ ent->start_addr = *iter;
+ ent->end_addr = *iter + size;
+ INIT_LIST_HEAD(&ent->list);
+ list_add_tail(&ent->list, &kprobe_blacklist);
+ }
+ return 0;
+}
+
/* Module notifier call back, checking kprobes on the module */
static int __kprobes kprobes_module_callback(struct notifier_block *nb,
unsigned long val, void *data)
@@ -2065,14 +2085,13 @@ 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;
- unsigned long offset = 0, size = 0;
- char *modname, namebuf[KSYM_NAME_LEN];
- const char *symbol_name;
- void *addr;
- struct kprobe_blackpoint *kb;

/* FIXME allocate the probe table, currently defined statically */
/* initialize all list heads */
@@ -2082,26 +2101,11 @@ static int __init init_kprobes(void)
raw_spin_lock_init(&(kretprobe_table_locks[i].lock));
}

- /*
- * Lookup and populate the kprobe_blacklist.
- *
- * Unlike the kretprobe blacklist, we'll need to determine
- * the range of addresses that belong to the said functions,
- * since a kprobe need not necessarily be at the beginning
- * of a function.
- */
- for (kb = kprobe_blacklist; kb->name != NULL; kb++) {
- kprobe_lookup_name(kb->name, addr);
- if (!addr)
- continue;
-
- kb->start_addr = (unsigned long)addr;
- symbol_name = kallsyms_lookup(kb->start_addr,
- &size, &offset, &modname, namebuf);
- if (!symbol_name)
- kb->range = 0;
- else
- kb->range = size;
+ 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");
}

if (kretprobe_blacklist_size) {
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 87c3bc4..05e7595 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2662,6 +2662,7 @@ asmlinkage void __sched notrace preempt_schedule(void)
barrier();
} while (need_resched());
}
+NOKPROBE_SYMBOL(preempt_schedule);
EXPORT_SYMBOL(preempt_schedule);
#endif /* CONFIG_PREEMPT */



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