xtensa: enable stack protector
The implementation is adopted from the ARM arch. GCC 7.3, 8 or newer is
required for building the xtensa kernel with SSP.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index eb1f196..fffe05b 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -15,6 +15,7 @@
select GENERIC_IRQ_SHOW
select GENERIC_PCI_IOMAP
select GENERIC_SCHED_CLOCK
+ select HAVE_CC_STACKPROTECTOR
select HAVE_DEBUG_KMEMLEAK
select HAVE_DMA_API_DEBUG
select HAVE_DMA_CONTIGUOUS
diff --git a/arch/xtensa/boot/lib/Makefile b/arch/xtensa/boot/lib/Makefile
index d2a7f48..2fe1829 100644
--- a/arch/xtensa/boot/lib/Makefile
+++ b/arch/xtensa/boot/lib/Makefile
@@ -15,6 +15,10 @@
CFLAGS_REMOVE_inffast.o = -pg
endif
+CFLAGS_REMOVE_inflate.o += -fstack-protector -fstack-protector-strong
+CFLAGS_REMOVE_zmem.o += -fstack-protector -fstack-protector-strong
+CFLAGS_REMOVE_inftrees.o += -fstack-protector -fstack-protector-strong
+CFLAGS_REMOVE_inffast.o += -fstack-protector -fstack-protector-strong
quiet_cmd_copy_zlib = COPY $@
cmd_copy_zlib = cat $< > $@
diff --git a/arch/xtensa/include/asm/stackprotector.h b/arch/xtensa/include/asm/stackprotector.h
new file mode 100644
index 0000000..e368f94
--- /dev/null
+++ b/arch/xtensa/include/asm/stackprotector.h
@@ -0,0 +1,40 @@
+/*
+ * GCC stack protector support.
+ *
+ * (This is directly adopted from the ARM implementation)
+ *
+ * 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 Xtensa. 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/xtensa/kernel/asm-offsets.c b/arch/xtensa/kernel/asm-offsets.c
index bcb5beb..3b119b3 100644
--- a/arch/xtensa/kernel/asm-offsets.c
+++ b/arch/xtensa/kernel/asm-offsets.c
@@ -76,6 +76,9 @@ int main(void)
DEFINE(TASK_PID, offsetof (struct task_struct, pid));
DEFINE(TASK_THREAD, offsetof (struct task_struct, thread));
DEFINE(TASK_THREAD_INFO, offsetof (struct task_struct, stack));
+#ifdef CONFIG_CC_STACKPROTECTOR
+ DEFINE(TASK_STACK_CANARY, offsetof(struct task_struct, stack_canary));
+#endif
DEFINE(TASK_STRUCT_SIZE, sizeof (struct task_struct));
/* offsets in thread_info struct */
diff --git a/arch/xtensa/kernel/entry.S b/arch/xtensa/kernel/entry.S
index a27a9a6..5caff07 100644
--- a/arch/xtensa/kernel/entry.S
+++ b/arch/xtensa/kernel/entry.S
@@ -1971,6 +1971,12 @@
s32i a1, a2, THREAD_SP # save stack pointer
#endif
+#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
+ movi a6, __stack_chk_guard
+ l32i a8, a3, TASK_STACK_CANARY
+ s32i a8, a6, 0
+#endif
+
/* Disable ints while we manipulate the stack pointer. */
irq_save a14, a3
diff --git a/arch/xtensa/kernel/process.c b/arch/xtensa/kernel/process.c
index ff4f0ec..8dd0593 100644
--- a/arch/xtensa/kernel/process.c
+++ b/arch/xtensa/kernel/process.c
@@ -58,6 +58,12 @@ void (*pm_power_off)(void) = NULL;
EXPORT_SYMBOL(pm_power_off);
+#ifdef CONFIG_CC_STACKPROTECTOR
+#include <linux/stackprotector.h>
+unsigned long __stack_chk_guard __read_mostly;
+EXPORT_SYMBOL(__stack_chk_guard);
+#endif
+
#if XTENSA_HAVE_COPROCESSORS
void coprocessor_release_all(struct thread_info *ti)