jprobes: make jprobes a little safer for users

I realise jprobes are a razor-blades-included type of interface, but that
doesn't mean we can't try and make them safer to use.  This guy I know once
wrote code like this:

struct jprobe jp = { .kp.symbol_name = "foo", .entry = "jprobe_foo" };

And then his kernel exploded. Oops.

This patch adds an arch hook, arch_deref_entry_point() (I don't like it
either) which takes the void * in a struct jprobe, and gives back the text
address that it represents.

We can then use that in register_jprobe() to check that the entry point we're
passed is actually in the kernel text, rather than just some random value.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Cc: Prasanna S Panchamukhi <prasanna@in.ibm.com>
Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 14 insertions, 4 deletions

diff --git a/arch/ia64/kernel/kprobes.c b/arch/ia64/kernel/kprobes.c
index 5bc46f15134..5dc98b5abcf 100644
--- a/arch/ia64/kernel/kprobes.c
+++ b/arch/ia64/kernel/kprobes.c
@@ -936,10 +936,15 @@ static void ia64_get_bsp_cfm(struct unw_frame_info *info, void *arg)
 	return;
 }
 
+unsigned long arch_deref_entry_point(void *entry)
+{
+	return ((struct fnptr *)entry)->ip;
+}
+
 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 {
 	struct jprobe *jp = container_of(p, struct jprobe, kp);
-	unsigned long addr = ((struct fnptr *)(jp->entry))->ip;
+	unsigned long addr = arch_deref_entry_point(jp->entry);
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 	struct param_bsp_cfm pa;
 	int bytes;
diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 0c96611f02f..440f5a87271 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -492,6 +492,13 @@ int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 	return ret;
 }
 
+#ifdef CONFIG_PPC64
+unsigned long arch_deref_entry_point(void *entry)
+{
+	return (unsigned long)(((func_descr_t *)entry)->entry);
+}
+#endif
+
 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 {
 	struct jprobe *jp = container_of(p, struct jprobe, kp);
@@ -500,11 +507,9 @@ int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 	memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
 
 	/* setup return addr to the jprobe handler routine */
+	regs->nip = arch_deref_entry_point(jp->entry);
 #ifdef CONFIG_PPC64
-	regs->nip = (unsigned long)(((func_descr_t *)jp->entry)->entry);
 	regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
-#else
-	regs->nip = (unsigned long)jp->entry;
 #endif
 
 	return 1;