gcc-plugins: arm-ssp: Prepare for THREAD_INFO_IN_TASK support

We will be enabling THREAD_INFO_IN_TASK support for ARM, which means
that we can no longer load the stack canary value by masking the stack
pointer and taking the copy that lives in thread_info. Instead, we will
be able to load it from the task_struct directly, by using the TPIDRURO
register which will hold the current task pointer when
THREAD_INFO_IN_TASK is in effect. This is much more straight-forward,
and allows us to declutter this code a bit while at it.

Note that this means that ARMv6 (non-v6K) SMP systems can no longer use
this feature, but those are quite rare to begin with, so this is a
reasonable trade off.

Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>

6 files changed, 2 insertions, 18 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index fc196421b2ce..ff3e64ae959e 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1600,7 +1600,7 @@ config XEN
 
 config STACKPROTECTOR_PER_TASK
 	bool "Use a unique stack canary value for each task"
-	depends on GCC_PLUGINS && STACKPROTECTOR && SMP && !XIP_DEFLATED_DATA
+	depends on GCC_PLUGINS && STACKPROTECTOR && THREAD_INFO_IN_TASK && !XIP_DEFLATED_DATA
 	select GCC_PLUGIN_ARM_SSP_PER_TASK
 	default y
 	help
diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index 847c31e7c368..b46e673a0ebe 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -273,11 +273,8 @@ ifeq ($(CONFIG_STACKPROTECTOR_PER_TASK),y)
 prepare: stack_protector_prepare
 stack_protector_prepare: prepare0
 	$(eval SSP_PLUGIN_CFLAGS := \
-		-fplugin-arg-arm_ssp_per_task_plugin-tso=$(shell	\
-			awk '{if ($$2 == "THREAD_SZ_ORDER") print $$3;}'\
-				include/generated/asm-offsets.h)	\
 		-fplugin-arg-arm_ssp_per_task_plugin-offset=$(shell	\
-			awk '{if ($$2 == "TI_STACK_CANARY") print $$3;}'\
+			awk '{if ($$2 == "TSK_STACK_CANARY") print $$3;}'\
 				include/generated/asm-offsets.h))
 	$(eval KBUILD_CFLAGS += $(SSP_PLUGIN_CFLAGS))
 	$(eval GCC_PLUGINS_CFLAGS += $(SSP_PLUGIN_CFLAGS))
diff --git a/arch/arm/include/asm/stackprotector.h b/arch/arm/include/asm/stackprotector.h
index 72a20c3a0a90..088d03161be5 100644
--- a/arch/arm/include/asm/stackprotector.h
+++ b/arch/arm/include/asm/stackprotector.h
@@ -39,8 +39,6 @@ static __always_inline void boot_init_stack_canary(void)
 	current->stack_canary = canary;
 #ifndef CONFIG_STACKPROTECTOR_PER_TASK
 	__stack_chk_guard = current->stack_canary;
-#else
-	current_thread_info()->stack_canary = current->stack_canary;
 #endif
 }
 
diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
index 9a18da3e10cc..f0cacc733231 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -55,9 +55,6 @@ struct thread_info {
 	struct task_struct	*task;		/* main task structure */
 	__u32			cpu;		/* cpu */
 	__u32			cpu_domain;	/* cpu domain */
-#ifdef CONFIG_STACKPROTECTOR_PER_TASK
-	unsigned long		stack_canary;
-#endif
 	struct cpu_context_save	cpu_context;	/* cpu context */
 	__u32			abi_syscall;	/* ABI type and syscall nr */
 	__u8			used_cp[16];	/* thread used copro */
diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
index a646a3f6440f..9c864ee76107 100644
--- a/arch/arm/kernel/asm-offsets.c
+++ b/arch/arm/kernel/asm-offsets.c
@@ -63,10 +63,6 @@ int main(void)
 #ifdef CONFIG_IWMMXT
   DEFINE(TI_IWMMXT_STATE,	offsetof(struct thread_info, fpstate.iwmmxt));
 #endif
-#ifdef CONFIG_STACKPROTECTOR_PER_TASK
-  DEFINE(TI_STACK_CANARY,	offsetof(struct thread_info, stack_canary));
-#endif
-  DEFINE(THREAD_SZ_ORDER,	THREAD_SIZE_ORDER);
   BLANK();
   DEFINE(S_R0,			offsetof(struct pt_regs, ARM_r0));
   DEFINE(S_R1,			offsetof(struct pt_regs, ARM_r1));
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 0e2d3051741e..cd73c216b272 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -269,10 +269,6 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,
 
 	thread_notify(THREAD_NOTIFY_COPY, thread);
 
-#ifdef CONFIG_STACKPROTECTOR_PER_TASK
-	thread->stack_canary = p->stack_canary;
-#endif
-
 	return 0;
 }