* [PATCH v2 1/2] powerpc: initial stack protector (-fstack-protector) support
2016-11-22 10:49 [PATCH v2 0/2] powerpc: stack protector (-fstack-protector) support Christophe Leroy
@ 2016-11-22 10:49 ` Christophe Leroy
2016-11-25 0:04 ` [v2, " Michael Ellerman
2016-11-22 10:49 ` [PATCH v2 2/2] powerpc/32: stack protector: change the canary value per task Christophe Leroy
1 sibling, 1 reply; 4+ messages in thread
From: Christophe Leroy @ 2016-11-22 10:49 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman, Scott Wood
Cc: linux-kernel, linuxppc-dev, Nicolas Pitre
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.pitre@linaro.org>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
arch/powerpc/Kconfig | 1 +
arch/powerpc/include/asm/stackprotector.h | 40 +++++++++++++++++++++++++++++++
arch/powerpc/kernel/Makefile | 4 ++++
arch/powerpc/kernel/process.c | 6 +++++
4 files changed, 51 insertions(+)
create mode 100644 arch/powerpc/include/asm/stackprotector.h
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index e119aca..6cb449c 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -164,6 +164,7 @@ config PPC
select ARCH_HAS_SCALED_CPUTIME if VIRT_CPU_ACCOUNTING_NATIVE
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..6720190
--- /dev/null
+++ b/arch/powerpc/include/asm/stackprotector.h
@@ -0,0 +1,40 @@
+/*
+ * 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 PPC. This unfortunately means that on SMP
+ * we cannot have a different canary value per task.
+ */
+
+#ifndef _ASM_STACKPROTECTOR_H
+#define _ASM_STACKPROTECTOR_H
+
+#include <linux/random.h>
+#include <linux/version.h>
+#include <asm/reg.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 ^= mftb();
+ 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 c3b3717..1d614bd 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -19,6 +19,10 @@ 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.
+CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector)
+
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 5dd056d..04885ce 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)
--
2.10.1
^ permalink raw reply [flat|nested] 4+ messages in thread* [PATCH v2 2/2] powerpc/32: stack protector: change the canary value per task
2016-11-22 10:49 [PATCH v2 0/2] powerpc: stack protector (-fstack-protector) support Christophe Leroy
2016-11-22 10:49 ` [PATCH v2 1/2] powerpc: initial " Christophe Leroy
@ 2016-11-22 10:49 ` Christophe Leroy
1 sibling, 0 replies; 4+ messages in thread
From: Christophe Leroy @ 2016-11-22 10:49 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman, Scott Wood
Cc: linux-kernel, linuxppc-dev, Nicolas Pitre
Partially copied from commit df0698be14c66 ("ARM: stack protector:
change the canary value per task")
A new random value for the canary is stored in the task struct whenever
a new task is forked. This is meant to allow for different canary values
per task. On powerpc, GCC expects the canary value to be found in a global
variable called __stack_chk_guard. So this variable has to be updated
with the value stored in the task struct whenever a task switch occurs.
Because the variable GCC expects is global, this cannot work on SMP
unfortunately. So, on SMP, the same initial canary value is kept
throughout, making this feature a bit less effective although it is still
useful.
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
arch/powerpc/kernel/asm-offsets.c | 3 +++
arch/powerpc/kernel/entry_32.S | 6 +++++-
2 files changed, 8 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index caec7bf..5c86030 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -91,6 +91,9 @@ int main(void)
DEFINE(TI_livepatch_sp, offsetof(struct thread_info, livepatch_sp));
#endif
+#ifdef CONFIG_CC_STACKPROTECTOR
+ DEFINE(TSK_STACK_CANARY, offsetof(struct task_struct, stack_canary));
+#endif
DEFINE(KSP, offsetof(struct thread_struct, ksp));
DEFINE(PT_REGS, offsetof(struct thread_struct, regs));
#ifdef CONFIG_BOOKE
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 3841d74..5742dbd 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -674,7 +674,11 @@ BEGIN_FTR_SECTION
mtspr SPRN_SPEFSCR,r0 /* restore SPEFSCR reg */
END_FTR_SECTION_IFSET(CPU_FTR_SPE)
#endif /* CONFIG_SPE */
-
+#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
+ lwz r0,TSK_STACK_CANARY(r2)
+ lis r4,__stack_chk_guard@ha
+ stw r0,__stack_chk_guard@l(r4)
+#endif
lwz r0,_CCR(r1)
mtcrf 0xFF,r0
/* r3-r12 are destroyed -- Cort */
--
2.10.1
^ permalink raw reply [flat|nested] 4+ messages in thread