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/Documentation/features/debug/stackprotector/arch-support.txt b/Documentation/features/debug/stackprotector/arch-support.txt
index d7acd7b..59a4c9f 100644 (file)
--- a/Documentation/features/debug/stackprotector/arch-support.txt
+++ b/Documentation/features/debug/stackprotector/arch-support.txt
@@ -35,5 +35,5 @@
     |          um: | TODO |
     |   unicore32: | TODO |
     |         x86: |  ok  |
-    |      xtensa: | TODO |
+    |      xtensa: |  ok  |
     -----------------------

diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index eb1f196..fffe05b 100644 (file)
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -15,6 +15,7 @@ config XTENSA
        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 (file)
--- a/arch/xtensa/boot/lib/Makefile
+++ b/arch/xtensa/boot/lib/Makefile
@@ -15,6 +15,10 @@ CFLAGS_REMOVE_inftrees.o = -pg
 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 (file)
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 (file)
--- 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 (file)
--- a/arch/xtensa/kernel/entry.S
+++ b/arch/xtensa/kernel/entry.S
@@ -1971,6 +1971,12 @@ ENTRY(_switch_to)
        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 (file)
--- 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)