kprobes: prevent probing of preempt_schedule()

Prohibit users from probing preempt_schedule().  One way of prohibiting the
user from probing functions is by marking such functions with __kprobes.  But
this method doesn't work for those functions, which are already marked to
different section like preempt_schedule() (belongs to __sched section).  So we
use blacklist approach to refuse user from probing these functions.

In blacklist approach we populate the blacklisted function's starting address
and its size in kprobe_blacklist structure.  Then we verify the user specified
address against start and end of the blacklisted function.  So any attempt to
register probe on blacklisted functions will be rejected.

[akpm@linux-foundation.org: build fix]
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Srinivasa DS <srinivasa@in.ibm.com>
Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Jim Keniston <jkenisto@us.ibm.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 52 insertions, 0 deletions

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index fcfb580c3afc..f02a4311768b 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -72,6 +72,18 @@ DEFINE_MUTEX(kprobe_mutex);		/* Protects kprobe_table */
 DEFINE_SPINLOCK(kretprobe_lock);        /* Protects kretprobe_inst_table */
 static DEFINE_PER_CPU(struct kprobe *, kprobe_instance) = NULL;
 
+/*
+ * 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
+ */
+struct kprobe_blackpoint kprobe_blacklist[] = {
+        {"preempt_schedule",},
+        {NULL}    /* Terminator */
+};
+
 #ifdef __ARCH_WANT_KPROBES_INSN_SLOT
 /*
  * kprobe->ainsn.insn points to the copy of the instruction to be
@@ -492,9 +504,22 @@ static int __kprobes register_aggr_kprobe(struct kprobe *old_p,
 
 static int __kprobes in_kprobes_functions(unsigned long addr)
 {
+        struct kprobe_blackpoint *kb;
+
         if (addr >= (unsigned long)__kprobes_text_start &&
             addr < (unsigned long)__kprobes_text_end)
                 return -EINVAL;
+        /*
+         * 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;
+                }
+        }
         return 0;
 }
 
@@ -811,6 +836,11 @@ void __kprobes unregister_kretprobe(struct kretprobe *rp)
 static int __init init_kprobes(void)
 {
         int i, err = 0;
+        unsigned long offset = 0, size = 0;
+        char *modname, namebuf[128];
+        const char *symbol_name;
+        void *addr;
+        struct kprobe_blackpoint *kb;
 
         /* FIXME allocate the probe table, currently defined statically */
         /* initialize all list heads */
@@ -819,6 +849,28 @@ static int __init init_kprobes(void)
                 INIT_HLIST_HEAD(&kretprobe_inst_table[i]);
         }
 
+        /*
+         * 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;
+        }
+
         if (kretprobe_blacklist_size) {
                 /* lookup the function address from its name */
                 for (i = 0; kretprobe_blacklist[i].name != NULL; i++) {