x86: clean up text_poke()

Clean up the codepath, remove alignment restrictions and do sanity
checking of the end result, to make sure we patched the right site.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/alternative.c

@@ -511,13 +511,17 @@ void *__kprobes text_poke(void *addr, const void *opcode, size_t len)
 	unsigned long flags;
 	char *vaddr;
 	int nr_pages = 2;
+	struct page *pages[2];
+	int i;
 
-	BUG_ON(len > sizeof(long));
-	BUG_ON((((long)addr + len - 1) & ~(sizeof(long) - 1))
-		- ((long)addr & ~(sizeof(long) - 1)));
-	if (core_kernel_text((unsigned long)addr)) {
-		struct page *pages[2] = { virt_to_page(addr),
-			virt_to_page(addr + PAGE_SIZE) };
+	if (!core_kernel_text((unsigned long)addr)) {
+		pages[0] = vmalloc_to_page(addr);
+		pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
+	} else {
+		pages[0] = virt_to_page(addr);
+		pages[1] = virt_to_page(addr + PAGE_SIZE);
+	}
+	BUG_ON(!pages[0]);
 	if (!pages[1])
 		nr_pages = 1;
 	vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
@@ -526,16 +530,10 @@ void *__kprobes text_poke(void *addr, const void *opcode, size_t len)
 	memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
 	local_irq_restore(flags);
 	vunmap(vaddr);
-	} else {
-		/*
-		 * modules are in vmalloc'ed memory, always writable.
-		 */
-		local_irq_save(flags);
-		memcpy(addr, opcode, len);
-		local_irq_restore(flags);
-	}
 	sync_core();
 	/* Could also do a CLFLUSH here to speed up CPU recovery; but
 	   that causes hangs on some VIA CPUs. */
+	for (i = 0; i < len; i++)
+		BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]);
 	return addr;
 }