Le 17/11/2016 à 12:05, Michael Ellerman a écrit :

Hi Michael,

I took your comments into account in v2. Shame on me, I forgot to add 
the list of changes from v1 to v2 in the commit log.

Christophe

Christophe Leroy [off-list ref] writes:

quoted

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

                             ^
                             PPC

quoted

+ * we cannot have a different canary value per task.
+ */
+
+#ifndef _ASM_STACKPROTECTOR_H
+#define _ASM_STACKPROTECTOR_H 1

We usually just define it, not define it to 1.

quoted

+
+#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;

What about mixing in an mftb() as well ?

quoted

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)

We've already assigned to CFLAGS_prom_init.o so I think you should be
using += not := shouldn't you?

Also it could just be a single line:

CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector)


cheers