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Date: Tue, 4 Mar 2008 14:26:37 +0530
From: Srinivasa DS <srinivasa@...ibm.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, ananth@...ibm.com,
Jim Keniston <jkenisto@...ibm.com>, srikar@...ux.vnet.ibm.com
Subject: Re: [RFC] [PATCH] To refuse users from probing preempt_schedule()
On Tuesday 04 March 2008 01:55:21 pm Andrew Morton wrote:
> On Mon, 25 Feb 2008 11:27:40 +0530 srinivasa <srinivasa@...ibm.com> wrote:
> > From: Srinivasa Ds <srinivasa@...ibm.com>
> >
> > This patch prohibits user 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.
> >
> > please let me know your comments.
>
> sparc64:
>
> kernel/kprobes.c: In function `in_kprobes_functions':
> kernel/kprobes.c:516: error: `kprobe_blacklist' undeclared (first use in
> this function) kernel/kprobes.c:516: error: (Each undeclared identifier is
> reported only once kernel/kprobes.c:516: error: for each function it
> appears in.)
> kernel/kprobes.c: In function `init_kprobes':
> kernel/kprobes.c:860: error: `kprobe_blacklist' undeclared (first use in
> this function)
>
> > ---
> > include/linux/kprobes.h | 7 ++++++
> > kernel/kprobes.c | 52
> > ++++++++++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 59 insertions(+)
> >
> > Index: linux-2.6.25-rc3/include/linux/kprobes.h
> > ===================================================================
> > --- linux-2.6.25-rc3.orig/include/linux/kprobes.h
> > +++ linux-2.6.25-rc3/include/linux/kprobes.h
> > @@ -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;
> > +};
> > +
>
> I'm assuming that the placement of this definition inside
> __ARCH_WANT_KPROBES_INSN_SLOT wqs accidental?
Yes Andrew. Sorry I over looked __ARCH_WANT_KPROBES_INSN_SLOT and placed the
struct kprobe_black_point in a wrong place.
Patch, that you have attached below looks good, but for your reference,
Iam attaching the modified patch below.
>
> --- a/kernel/kprobes.c~kprobes-prevent-probing-of-preempt_schedule-fix
> +++ a/kernel/kprobes.c
> @@ -72,6 +72,18 @@ DEFINE_MUTEX(kprobe_mutex); /* Protects
> 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
> @@ -89,18 +101,6 @@ struct kprobe_insn_page {
> int ngarbage;
> };
>
> -/*
> - * 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 */
> -};
> -
> enum kprobe_slot_state {
> SLOT_CLEAN = 0,
> SLOT_DIRTY = 1,
> _
---
include/linux/kprobes.h | 7 ++++++
kernel/kprobes.c | 51
++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 58 insertions(+)
Index: linux-2.6.25-rc3/include/linux/kprobes.h
===================================================================
--- linux-2.6.25-rc3.orig/include/linux/kprobes.h
+++ linux-2.6.25-rc3/include/linux/kprobes.h
@@ -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,
Index: linux-2.6.25-rc3/kernel/kprobes.c
===================================================================
--- linux-2.6.25-rc3.orig/kernel/kprobes.c
+++ linux-2.6.25-rc3/kernel/kprobes.c
@@ -72,6 +72,17 @@ DEFINE_MUTEX(kprobe_mutex); /* Protects
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 +503,22 @@ static int __kprobes register_aggr_kprob
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;
}
@@ -805,6 +829,11 @@ void __kprobes unregister_kretprobe(stru
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 */
@@ -813,6 +842,28 @@ 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++) {
--
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