to the compiler, so it will attempt to add canary checks regardless
of the static branch state.
-config RANDOMIZE_KSTACK_OFFSET_DEFAULT
- bool "Randomize kernel stack offset on syscall entry"
+config RANDOMIZE_KSTACK_OFFSET
+ bool "Support for randomizing kernel stack offset on syscall entry" if EXPERT
+ default y
depends on HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
help
The kernel stack offset can be randomized (after pt_regs) by
roughly 5 bits of entropy, frustrating memory corruption
attacks that depend on stack address determinism or
- cross-syscall address exposures. This feature is controlled
- by kernel boot param "randomize_kstack_offset=on/off", and this
- config chooses the default boot state.
+ cross-syscall address exposures.
+
+ The feature is controlled via the "randomize_kstack_offset=on/off"
+ kernel boot param, and if turned off has zero overhead due to its use
+ of static branches (see JUMP_LABEL).
+
+ If unsure, say Y.
+
+config RANDOMIZE_KSTACK_OFFSET_DEFAULT
+ bool "Default state of kernel stack offset randomization"
+ depends on RANDOMIZE_KSTACK_OFFSET
+ help
+ Kernel stack offset randomization is controlled by kernel boot param
+ "randomize_kstack_offset=on/off", and this config chooses the default
+ boot state.
config ARCH_OPTIONAL_KERNEL_RWX
def_bool n
#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>
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
pti_init();
}
-#ifdef CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
+#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET
DEFINE_STATIC_KEY_MAYBE_RO(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT,
randomize_kstack_offset);
DEFINE_PER_CPU(u32, kstack_offset);