Partialy copied from commit c743f38013aef ("ARM: initial stack protector
(-fstack-protector) support")
This is the very basic stuff without the changing canary upon
task switch yet. Just the Kconfig option and a constant canary
value initialized at boot time.
Cc: Nicolas Pitre <nicolas.pi...@linaro.org>
Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr>
---
arch/powerpc/Kconfig | 1 +
arch/powerpc/include/asm/stackprotector.h | 38 +++++++++++++++++++++++++++++++
arch/powerpc/kernel/Makefile | 5 ++++
arch/powerpc/kernel/process.c | 6 +++++
4 files changed, 50 insertions(+)
create mode 100644 arch/powerpc/include/asm/stackprotector.h
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 59e53f4..2947dab 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -162,6 +162,7 @@ config PPC
select HAVE_VIRT_CPU_ACCOUNTING
select HAVE_ARCH_HARDENED_USERCOPY
select HAVE_KERNEL_GZIP
+ select HAVE_CC_STACKPROTECTOR
config GENERIC_CSUM
def_bool CPU_LITTLE_ENDIAN
diff --git a/arch/powerpc/include/asm/stackprotector.h
b/arch/powerpc/include/asm/stackprotector.h
new file mode 100644
index 0000000..de00332
--- /dev/null
+++ b/arch/powerpc/include/asm/stackprotector.h
@@ -0,0 +1,38 @@
+/*
+ * GCC stack protector support.
+ *
+ * Stack protector works by putting predefined pattern at the start of
+ * the stack frame and verifying that it hasn't been overwritten when
+ * returning from the function. The pattern is called stack canary
+ * and gcc expects it to be defined by a global variable called
+ * "__stack_chk_guard" on ARM. This unfortunately means that on SMP
+ * we cannot have a different canary value per task.
+ */
+
+#ifndef _ASM_STACKPROTECTOR_H
+#define _ASM_STACKPROTECTOR_H 1
+
+#include <linux/random.h>
+#include <linux/version.h>
+
+extern unsigned long __stack_chk_guard;
+
+/*
+ * Initialize the stackprotector canary value.
+ *
+ * NOTE: this must only be called from functions that never return,
+ * and it must always be inlined.
+ */
+static __always_inline void boot_init_stack_canary(void)
+{
+ unsigned long canary;
+
+ /* Try to get a semi random initial value. */
+ get_random_bytes(&canary, sizeof(canary));
+ canary ^= LINUX_VERSION_CODE;
+
+ current->stack_canary = canary;
+ __stack_chk_guard = current->stack_canary;
+}
+
+#endif /* _ASM_STACKPROTECTOR_H */
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index e59ed6a..4a62179 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -19,6 +19,11 @@ CFLAGS_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
+# -fstack-protector triggers protection checks in this code,
+# but it is being used too early to link to meaningful stack_chk logic.
+nossp_flags := $(call cc-option, -fno-stack-protector)
+CFLAGS_prom_init.o := $(nossp_flags)
+
ifdef CONFIG_FUNCTION_TRACER
# Do not trace early boot code
CFLAGS_REMOVE_cputable.o = -mno-sched-epilog $(CC_FLAGS_FTRACE)
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index ce8a26a..ba8f32a 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -64,6 +64,12 @@
#include <linux/kprobes.h>
#include <linux/kdebug.h>
+#ifdef CONFIG_CC_STACKPROTECTOR
+#include <linux/stackprotector.h>
+unsigned long __stack_chk_guard __read_mostly;
+EXPORT_SYMBOL(__stack_chk_guard);
+#endif
+
/* Transactional Memory debug */
#ifdef TM_DEBUG_SW
#define TM_DEBUG(x...) printk(KERN_INFO x)
--
2.1.0
