[PATCH v2 2/4] xen: common: add ability to enable stack protector

[Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>]

Both GCC and Clang support -fstack-protector feature, which add stack
canaries to functions where stack corruption is possible. This patch
makes general preparations to enable this feature on different
supported architectures:

 - Added CONFIG_HAS_STACK_PROTECTOR option so each architecture
   can enable this feature individually
 - Added user-selectable CONFIG_STACK_PROTECTOR option
 - Implemented code that sets up random stack canary and a basic
   handler for stack protector failures

Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>

---

Changes in v2:
 - Moved changes to EMBEDDED_EXTRA_CFLAGS into separate patch
 - Renamed stack_protector.c to stack-protector.c
 - Renamed stack_protector.h to stack-protector.h
 - Removed #ifdef CONFIG_X86 in stack-protector.h
 - Updated comment in stack-protector.h
   (also, we can't call boot_stack_chk_guard_setup() from asm code in
   general case, because it calls get_random() and get_random() may
   depend in per_cpu infrastructure, which is initialized later)
 - Fixed coding style
 - Moved CONFIG_STACK_PROTECTOR into newly added "Compiler options"
 submenu
 - Marked __stack_chk_guard as __ro_after_init
---
 xen/Makefile                      |  4 ++++
 xen/common/Kconfig                | 17 +++++++++++++++++
 xen/common/Makefile               |  1 +
 xen/common/stack-protector.c      | 10 ++++++++++
 xen/include/xen/stack-protector.h | 29 +++++++++++++++++++++++++++++
 5 files changed, 61 insertions(+)
 create mode 100644 xen/common/stack-protector.c
 create mode 100644 xen/include/xen/stack-protector.h

diff --git a/xen/Makefile b/xen/Makefile
index 34ed8c0fc7..0de0101fd0 100644
--- a/xen/Makefile
+++ b/xen/Makefile
@@ -432,7 +432,11 @@ else
 CFLAGS_UBSAN :=
 endif
 
+ifeq ($(CONFIG_STACK_PROTECTOR),y)
+CFLAGS += -fstack-protector
+else
 CFLAGS += -fno-stack-protector
+endif
 
 ifeq ($(CONFIG_LTO),y)
 CFLAGS += -flto
diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index 90268d9249..64fd04f805 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -86,6 +86,9 @@ config HAS_UBSAN
 config HAS_VMAP
        bool
 
+config HAS_STACK_PROTECTOR
+       bool
+
 config MEM_ACCESS_ALWAYS_ON
        bool
 
@@ -213,6 +216,20 @@ config SPECULATIVE_HARDEN_LOCK
 
 endmenu
 
+menu "Compiler options"
+
+config STACK_PROTECTOR
+       bool "Stack protection"
+       depends on HAS_STACK_PROTECTOR
+       help
+         Use compiler's option -fstack-protector (supported both by GCC
+         and Clang) to generate code that checks for corrupted stack
+         and halts the system in case of any problems.
+
+         Please note that this option will impair performance.
+
+endmenu
+
 config DIT_DEFAULT
        bool "Data Independent Timing default"
        depends on HAS_DIT
diff --git a/xen/common/Makefile b/xen/common/Makefile
index b279b09bfb..ceb5b2f32b 100644
--- a/xen/common/Makefile
+++ b/xen/common/Makefile
@@ -45,6 +45,7 @@ obj-y += shutdown.o
 obj-y += softirq.o
 obj-y += smp.o
 obj-y += spinlock.o
+obj-$(CONFIG_STACK_PROTECTOR) += stack-protector.o
 obj-y += stop_machine.o
 obj-y += symbols.o
 obj-y += tasklet.o
diff --git a/xen/common/stack-protector.c b/xen/common/stack-protector.c
new file mode 100644
index 0000000000..b258590d3a
--- /dev/null
+++ b/xen/common/stack-protector.c
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <xen/lib.h>
+#include <xen/random.h>
+
+unsigned long __ro_after_init __stack_chk_guard;
+
+void __stack_chk_fail(void)
+{
+    panic("Detected stack corruption\n");
+}
diff --git a/xen/include/xen/stack-protector.h 
b/xen/include/xen/stack-protector.h
new file mode 100644
index 0000000000..779d7cf9ec
--- /dev/null
+++ b/xen/include/xen/stack-protector.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef XEN__STACK_PROTECTOR_H
+#define XEN__STACK_PROTECTOR_H
+
+#ifdef CONFIG_STACKPROTECTOR
+
+extern unsigned long __stack_chk_guard;
+
+/*
+ * This function should be always inlined. Also it should be called
+ * from a function that never returns or a function that with
+ * stack-protector disabled.
+ */
+static always_inline void boot_stack_chk_guard_setup(void)
+{
+       __stack_chk_guard = get_random();
+       if (BITS_PER_LONG == 64)
+               __stack_chk_guard |= ((unsigned long)get_random()) << 32;
+}
+
+#else
+
+static inline void boot_stack_chk_guard_setup(void) {}
+
+#endif /* CONFIG_STACKPROTECTOR  */
+
+#endif /* XEN__STACK_PROTECTOR_H */
+
-- 
2.47.1