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Commit 3d8d996e authored by Srinivasa Ds's avatar Srinivasa Ds Committed by Linus Torvalds
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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: default avatarSrinivasa DS <srinivasa@in.ibm.com>
Signed-off-by: default avatarAnanth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: default avatarJim Keniston <jkenisto@us.ibm.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0341a4d0

include/linux/kprobes.h

+7 −0
Original line number Diff line number Diff line
@@ -173,6 +173,13 @@ struct kretprobe_blackpoint { 
	const char *name;

	void *addr;

};



struct kprobe_blackpoint {

	const char *name;

	unsigned long start_addr;

	unsigned long range;

};



extern struct kretprobe_blackpoint kretprobe_blacklist[];



static inline void kretprobe_assert(struct kretprobe_instance *ri,

kernel/kprobes.c

+52 −0
Original line number Diff line number Diff line
@@ -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++) {