[PATCH v6 3/4] xen: arm: enable stack protector feature

[Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>]

Enable previously added CONFIG_STACK_PROTECTOR feature for ARM
platform. Initialize stack protector magic value very early, at the
very beginning of start_xen() function.

We want to do this early because prior to that
boot_stack_chk_guard_setup() call, default stack protector guard value
is used. While it is fine for general development and testing, it does
not provide highest security level, because potential attacker will
know the default value and can alter a payload, so correct stack
guard value will be placed in the correct position.

Apart from that argument, boot_stack_chk_guard_setup() should be
called prior to enabling secondary CPUs to avoid race with them.

Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
Acked-by: Julien Grall <jgrall@xxxxxxxxxx>

---

Changes in v6:

 - Expanded the commit message
 - Added Julien's A-b tag

Changes in v5:

 - Call boot_stack_chk_guard_setup() from start_xen()
   instead of early ASM
---
 xen/arch/arm/Kconfig | 1 +
 xen/arch/arm/setup.c | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
index a26d3e1182..8f1a3c7d74 100644
--- a/xen/arch/arm/Kconfig
+++ b/xen/arch/arm/Kconfig
@@ -16,6 +16,7 @@ config ARM
        select GENERIC_UART_INIT
        select HAS_ALTERNATIVE if HAS_VMAP
        select HAS_DEVICE_TREE
+       select HAS_STACK_PROTECTOR
        select HAS_UBSAN
 
 config ARCH_DEFCONFIG
diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index c1f2d1b89d..0dca691207 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -30,6 +30,7 @@
 #include <xen/virtual_region.h>
 #include <xen/version.h>
 #include <xen/vmap.h>
+#include <xen/stack-protector.h>
 #include <xen/trace.h>
 #include <xen/libfdt/libfdt-xen.h>
 #include <xen/acpi.h>
@@ -305,6 +306,8 @@ void asmlinkage __init start_xen(unsigned long fdt_paddr)
     struct domain *d;
     int rc, i;
 
+    boot_stack_chk_guard_setup();
+
     dcache_line_bytes = read_dcache_line_bytes();
 
     percpu_init_areas();
-- 
2.47.1