ARM: probes: avoid adding kprobes to sensitive kernel-entry/exit code

Avoid adding kprobes to any of the kernel entry/exit or startup
assembly code, or code in the identity-mapped region.  This code does
not conform to the standard C conventions, which means that the
expectations of the kprobes code is not forfilled.

Placing kprobes at some of these locations results in the kernel trying
to return to userspace addresses while retaining the CPU in kernel mode.

Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

arch/arm/probes/kprobes/core.c

@@ -32,6 +32,7 @@
 #include <linux/percpu.h>
 #include <linux/bug.h>
 #include <asm/patch.h>
+#include <asm/sections.h>
 
 #include "../decode-arm.h"
 #include "../decode-thumb.h"
@@ -64,9 +65,6 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 	int is;
 	const struct decode_checker **checkers;
 
-	if (in_exception_text(addr))
-		return -EINVAL;
-
 #ifdef CONFIG_THUMB2_KERNEL
 	thumb = true;
 	addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
@@ -680,3 +678,13 @@ int __init arch_init_kprobes()
 #endif
 	return 0;
 }
+
+bool arch_within_kprobe_blacklist(unsigned long addr)
+{
+	void *a = (void *)addr;
+
+	return __in_irqentry_text(addr) ||
+	       in_entry_text(addr) ||
+	       in_idmap_text(addr) ||
+	       memory_contains(__kprobes_text_start, __kprobes_text_end, a, 1);
+}