mm/huge_memory: streamline COW logic in do_huge_pmd_wp_page()

[linux-2.6-microblaze.git] / include / linux / randomize_kstack.h

diff --git a/include/linux/randomize_kstack.h b/include/linux/randomize_kstack.h
index bebc911..1468caf 100644 (file)
--- a/include/linux/randomize_kstack.h
+++ b/include/linux/randomize_kstack.h
@@ -2,6 +2,7 @@
 #ifndef _LINUX_RANDOMIZE_KSTACK_H
 #define _LINUX_RANDOMIZE_KSTACK_H
 
+#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET
 #include <linux/kernel.h>
 #include <linux/jump_label.h>
 #include <linux/percpu-defs.h>
@@ -16,8 +17,20 @@ DECLARE_PER_CPU(u32, kstack_offset);
  * alignment. Also, since this use is being explicitly masked to a max of
  * 10 bits, stack-clash style attacks are unlikely. For more details see
  * "VLAs" in Documentation/process/deprecated.rst
+ *
+ * The normal __builtin_alloca() is initialized with INIT_STACK_ALL (currently
+ * only with Clang and not GCC). Initializing the unused area on each syscall
+ * entry is expensive, and generating an implicit call to memset() may also be
+ * problematic (such as in noinstr functions). Therefore, if the compiler
+ * supports it (which it should if it initializes allocas), always use the
+ * "uninitialized" variant of the builtin.
  */
-void *__builtin_alloca(size_t size);
+#if __has_builtin(__builtin_alloca_uninitialized)
+#define __kstack_alloca __builtin_alloca_uninitialized
+#else
+#define __kstack_alloca __builtin_alloca
+#endif
+
 /*
  * Use, at most, 10 bits of entropy. We explicitly cap this to keep the
  * "VLA" from being unbounded (see above). 10 bits leaves enough room for
@@ -36,7 +49,7 @@ void *__builtin_alloca(size_t size);
        if (static_branch_maybe(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, \
                                &randomize_kstack_offset)) {            \
                u32 offset = raw_cpu_read(kstack_offset);               \
-               u8 *ptr = __builtin_alloca(KSTACK_OFFSET_MAX(offset));  \
+               u8 *ptr = __kstack_alloca(KSTACK_OFFSET_MAX(offset));   \
                /* Keep allocation even after "ptr" loses scope. */     \
                asm volatile("" :: "r"(ptr) : "memory");                \
        }                                                               \
@@ -50,5 +63,9 @@ void *__builtin_alloca(size_t size);
                raw_cpu_write(kstack_offset, offset);                   \
        }                                                               \
 } while (0)
+#else /* CONFIG_RANDOMIZE_KSTACK_OFFSET */
+#define add_random_kstack_offset()             do { } while (0)
+#define choose_random_kstack_offset(rand)      do { } while (0)
+#endif /* CONFIG_RANDOMIZE_KSTACK_OFFSET */
 
 #endif