mm/execmem: Unify early execmem_cache behaviour

Early kernel memory is RWX, only at the end of early boot (before SMP)
do we mark things ROX. Have execmem_cache mirror this behaviour for
early users.

This avoids having to remember what code is execmem and what is not --
we can poke everything with impunity ;-) Also performance for not
having to do endless text_poke_mm switches.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>

Author: Peter Zijlstra

arch/x86/mm/init_32.c

@@ -30,6 +30,7 @@
 #include <linux/initrd.h>
 #include <linux/cpumask.h>
 #include <linux/gfp.h>
+#include <linux/execmem.h>
 
 #include <asm/asm.h>
 #include <asm/bios_ebda.h>
@@ -755,6 +756,8 @@ void mark_rodata_ro(void)
 	pr_info("Write protecting kernel text and read-only data: %luk\n",
 		size >> 10);
 
+	execmem_cache_make_ro();
+
 	kernel_set_to_readonly = 1;
 
 #ifdef CONFIG_CPA_DEBUG

arch/x86/mm/init_64.c

@@ -34,6 +34,7 @@
 #include <linux/gfp.h>
 #include <linux/kcore.h>
 #include <linux/bootmem_info.h>
+#include <linux/execmem.h>
 
 #include <asm/processor.h>
 #include <asm/bios_ebda.h>
@@ -1391,6 +1392,8 @@ void mark_rodata_ro(void)
 	       (end - start) >> 10);
 	set_memory_ro(start, (end - start) >> PAGE_SHIFT);
 
+	execmem_cache_make_ro();
+
 	kernel_set_to_readonly = 1;
 
 	/*

include/linux/execmem.h

@@ -53,7 +53,7 @@ enum execmem_range_flags {
 	EXECMEM_ROX_CACHE	= (1 << 1),
 };
 
-#ifdef CONFIG_ARCH_HAS_EXECMEM_ROX
+#if defined(CONFIG_ARCH_HAS_EXECMEM_ROX) && defined(CONFIG_EXECMEM)
 /**
  * execmem_fill_trapping_insns - set memory to contain instructions that
  *				 will trap
@@ -93,9 +93,15 @@ int execmem_make_temp_rw(void *ptr, size_t size);
  * Return: 0 on success or negative error code on failure.
  */
 int execmem_restore_rox(void *ptr, size_t size);
+
+/*
+ * Called from mark_readonly(), where the system transitions to ROX.
+ */
+void execmem_cache_make_ro(void);
 #else
 static inline int execmem_make_temp_rw(void *ptr, size_t size) { return 0; }
 static inline int execmem_restore_rox(void *ptr, size_t size) { return 0; }
+static inline void execmem_cache_make_ro(void) { }
 #endif
 
 /**

mm/execmem.c

@@ -254,6 +254,34 @@ static void *__execmem_cache_alloc(struct execmem_range *range, size_t size)
 	return ptr;
 }
 
+static bool execmem_cache_rox = false;
+
+void execmem_cache_make_ro(void)
+{
+	struct maple_tree *free_areas = &execmem_cache.free_areas;
+	struct maple_tree *busy_areas = &execmem_cache.busy_areas;
+	MA_STATE(mas_free, free_areas, 0, ULONG_MAX);
+	MA_STATE(mas_busy, busy_areas, 0, ULONG_MAX);
+	struct mutex *mutex = &execmem_cache.mutex;
+	void *area;
+
+	execmem_cache_rox = true;
+
+	mutex_lock(mutex);
+
+	mas_for_each(&mas_free, area, ULONG_MAX) {
+		unsigned long pages = mas_range_len(&mas_free) >> PAGE_SHIFT;
+		set_memory_ro(mas_free.index, pages);
+	}
+
+	mas_for_each(&mas_busy, area, ULONG_MAX) {
+		unsigned long pages = mas_range_len(&mas_busy) >> PAGE_SHIFT;
+		set_memory_ro(mas_busy.index, pages);
+	}
+
+	mutex_unlock(mutex);
+}
+
 static int execmem_cache_populate(struct execmem_range *range, size_t size)
 {
 	unsigned long vm_flags = VM_ALLOW_HUGE_VMAP;
@@ -274,9 +302,15 @@ static int execmem_cache_populate(struct execmem_range *range, size_t size)
 	/* fill memory with instructions that will trap */
 	execmem_fill_trapping_insns(p, alloc_size, /* writable = */ true);
 
-	err = set_memory_rox((unsigned long)p, vm->nr_pages);
-	if (err)
-		goto err_free_mem;
+	if (execmem_cache_rox) {
+		err = set_memory_rox((unsigned long)p, vm->nr_pages);
+		if (err)
+			goto err_free_mem;
+	} else {
+		err = set_memory_x((unsigned long)p, vm->nr_pages);
+		if (err)
+			goto err_free_mem;
+	}
 
 	err = execmem_cache_add(p, alloc_size);
 	if (err)