[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Xen-devel] [PATCH v2] x86/xen: init %gs very early to avoid page faults with stack protector



When running as Xen pv guest %gs is initialized some time after
C code is started. Depending on stack protector usage this might be
too late, resulting in page faults.

So setup %gs and MSR_GS_BASE in assembly code already.

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 arch/x86/xen/xen-head.S | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index 497cc55a0c16..96f26e026783 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -9,7 +9,9 @@
 
 #include <asm/boot.h>
 #include <asm/asm.h>
+#include <asm/msr.h>
 #include <asm/page_types.h>
+#include <asm/percpu.h>
 #include <asm/unwind_hints.h>
 
 #include <xen/interface/elfnote.h>
@@ -35,6 +37,20 @@ ENTRY(startup_xen)
        mov %_ASM_SI, xen_start_info
        mov $init_thread_union+THREAD_SIZE, %_ASM_SP
 
+#ifdef CONFIG_X86_64
+       /* Set up %gs.
+        *
+        * The base of %gs always points to the bottom of the irqstack
+        * union.  If the stack protector canary is enabled, it is
+        * located at %gs:40.  Note that, on SMP, the boot cpu uses
+        * init data section till per cpu areas are set up.
+        */
+       movl    $MSR_GS_BASE,%ecx
+       movq    $INIT_PER_CPU_VAR(irq_stack_union),%rax
+       cdq
+       wrmsr
+#endif
+
        jmp xen_start_kernel
 END(startup_xen)
        __FINIT
-- 
2.13.6


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel

 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.