powerpc/kprobes: Blacklist exception handlers

Introduce __head_end to mark end of the early fixed sections and use it to
blacklist all exception handlers from kprobes.

mpe: We do not need to do anything special for relocatable kernels, where the
exception vectors are split from the main kernel, as the split vectors are
already excluded by the check for kernel_text_address().

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
[mpe: Move __head_end outside #ifdef 64-bit to unbreak the 32-bit build]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/sections.h

@@ -6,6 +6,8 @@
 #include <linux/uaccess.h>
 #include <asm-generic/sections.h>
 
+extern char __head_end[];
+
 #ifdef __powerpc64__
 
 extern char __start_interrupts[];

arch/powerpc/kernel/kprobes.c

@@ -35,6 +35,7 @@
 #include <asm/code-patching.h>
 #include <asm/cacheflush.h>
 #include <asm/sstep.h>
+#include <asm/sections.h>
 #include <linux/uaccess.h>
 
 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
@@ -42,6 +43,14 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
 
 struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
 
+bool arch_within_kprobe_blacklist(unsigned long addr)
+{
+	return  (addr >= (unsigned long)__kprobes_text_start &&
+		 addr < (unsigned long)__kprobes_text_end) ||
+		(addr >= (unsigned long)_stext &&
+		 addr < (unsigned long)__head_end);
+}
+
 int arch_prepare_kprobe(struct kprobe *p)
 {
 	int ret = 0;

arch/powerpc/kernel/vmlinux.lds.S

@@ -77,6 +77,8 @@ SECTIONS
 #endif
 	} :kernel
 
+	__head_end = .;
+
 	/*
 	 * If the build dies here, it's likely code in head_64.S is referencing
 	 * labels it can't reach, and the linker inserting stubs without the