Subject: [PATCH 2/2] arm64: Clear the stack

From: [email-masked] (Laura Abbott)
Date: Wed, 18 Jul 2018 14:10:13 -0700

Implementation of stackleak based heavily on the x86 version

Signed-off-by: Laura Abbott <[email-masked]>
---
Since last time: Minor style cleanups. Re-wrote check_alloca to
correctly handle all stack types. While doing that, I also realized
current_top_of_stack was incorrect so I fixed that as well.
---
 arch/arm64/Kconfig                    |  1 +
 arch/arm64/include/asm/processor.h    | 17 ++++++++++++++
 arch/arm64/kernel/entry.S             |  7 ++++++
 arch/arm64/kernel/process.c           | 32 +++++++++++++++++++++++++++
 arch/arm64/kvm/hyp/Makefile           |  3 ++-
 drivers/firmware/efi/libstub/Makefile |  3 ++-
 include/linux/stackleak.h             |  1 +
 7 files changed, 62 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 42c090cf0292..216d36a49ab5 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -96,6 +96,7 @@ config ARM64
 	select HAVE_ARCH_MMAP_RND_BITS
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
 	select HAVE_ARCH_SECCOMP_FILTER
+	select HAVE_ARCH_STACKLEAK
 	select HAVE_ARCH_THREAD_STRUCT_WHITELIST
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index a73ae1e49200..4f3062ee22c6 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -266,5 +266,22 @@ extern void __init minsigstksz_setup(void);
 #define SVE_SET_VL(arg)	sve_set_current_vl(arg)
 #define SVE_GET_VL()	sve_get_current_vl()
 
+/*
+ * For CONFIG_STACKLEAK
+ *
+ * These need to be macros because otherwise we get stuck in a nightmare
+ * of header definitions for the use of task_stack_page.
+ */
+
+#define current_top_of_stack()		\
+({					\
+	unsigned long _low = 0;		\
+	unsigned long _high = 0;	\
+					\
+	current_stack_type(current, current_stack_pointer, &_low, &_high); \
+	_high;	\
+})
+#define on_thread_stack()	(on_task_stack(current, current_stack_pointer, NULL, NULL))
+
 #endif /* __ASSEMBLY__ */
 #endif /* __ASM_PROCESSOR_H */
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 28ad8799406f..67d12016063d 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -431,6 +431,11 @@ tsk	.req	x28		// current thread_info
 
 	.text
 
+	.macro	stackleak_erase
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+	bl	stackleak_erase
+#endif
+	.endm
 /*
  * Exception vectors.
  */
@@ -910,6 +915,7 @@ ret_fast_syscall:
 	and	x2, x1, #_TIF_WORK_MASK
 	cbnz	x2, work_pending
 	enable_step_tsk x1, x2
+	stackleak_erase
 	kernel_exit 0
 ret_fast_syscall_trace:
 	enable_daif
@@ -936,6 +942,7 @@ ret_to_user:
 	cbnz	x2, work_pending
 finish_ret_to_user:
 	enable_step_tsk x1, x2
+	stackleak_erase
 	kernel_exit 0
 ENDPROC(ret_to_user)
 
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index e10bc363f533..904defa36689 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -493,3 +493,35 @@ void arch_setup_new_exec(void)
 {
 	current->mm->context.flags = is_compat_task() ? MMCF_AARCH32 : 0;
 }
+
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+void __used stackleak_check_alloca(unsigned long size)
+{
+	unsigned long stack_left;
+	enum stack_type type;
+	unsigned long current_sp = current_stack_pointer;
+	unsigned long low, high;
+
+	type = current_stack_type(current, current_sp, &low, &high);
+	BUG_ON(type == STACK_TYPE_UNKNOWN);
+
+	stack_left = current_sp - low;
+
+	if (size >= stack_left) {
+		/*
+		 * Kernel stack depth overflow is detected, let's report that.
+		 * If CONFIG_VMAP_STACK is enabled, we can safely use BUG().
+		 * If CONFIG_VMAP_STACK is disabled, BUG() handling can corrupt
+		 * the neighbour memory. CONFIG_SCHED_STACK_END_CHECK calls
+		 * panic() in a similar situation, so let's do the same if that
+		 * option is on. Otherwise just use BUG() and hope for the best.
+		 */
+#if !defined(CONFIG_VMAP_STACK) && defined(CONFIG_SCHED_STACK_END_CHECK)
+		panic("alloca() over the kernel stack boundary\n");
+#else
+		BUG();
+#endif
+	}
+}
+EXPORT_SYMBOL(stackleak_check_alloca);
+#endif
diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
index 4313f7475333..2fabc2dc1966 100644
--- a/arch/arm64/kvm/hyp/Makefile
+++ b/arch/arm64/kvm/hyp/Makefile
@@ -3,7 +3,8 @@
 # Makefile for Kernel-based Virtual Machine module, HYP part
 #
 
-ccflags-y += -fno-stack-protector -DDISABLE_BRANCH_PROFILING
+ccflags-y += -fno-stack-protector -DDISABLE_BRANCH_PROFILING \
+		$(DISABLE_STACKLEAK_PLUGIN)
 
 KVM=../../../../virt/kvm
 
diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index a34e9290a699..25dd2a14560d 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -20,7 +20,8 @@ cflags-$(CONFIG_EFI_ARMSTUB)	+= -I$(srctree)/scripts/dtc/libfdt
 KBUILD_CFLAGS			:= $(cflags-y) -DDISABLE_BRANCH_PROFILING \
 				   -D__NO_FORTIFY \
 				   $(call cc-option,-ffreestanding) \
-				   $(call cc-option,-fno-stack-protector)
+				   $(call cc-option,-fno-stack-protector) \
+				   $(DISABLE_STACKLEAK_PLUGIN)
 
 GCOV_PROFILE			:= n
 KASAN_SANITIZE			:= n
diff --git a/include/linux/stackleak.h b/include/linux/stackleak.h
index b911b973d328..08420ec6b7c3 100644
--- a/include/linux/stackleak.h
+++ b/include/linux/stackleak.h
@@ -5,6 +5,7 @@
 #include <linux/sched.h>
 #include <linux/sched/task_stack.h>
 
+#include <asm/stacktrace.h>
 /*
  * Check that the poison value points to the unused hole in the
  * virtual memory map for your platform.
-- 
2.17.1