xen/x86-64: fix breakpoints and hardware watchpoints

Native x86-64 uses the IST mechanism to run int3 and debug traps on
an alternative stack.  Xen does not do this, and so the frames were
being misinterpreted by the ptrace code.  This change special-cases
these two exceptions by using Xen variants which run on the normal
kernel stack properly.

Impact: avoid crash or bad data when IST trap is invoked under Xen
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

1 files changed, 18 insertions, 1 deletions

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 12a3159333bc..7566e13c0cac 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -20,6 +20,7 @@
 #include <linux/delay.h>
 #include <linux/start_kernel.h>
 #include <linux/sched.h>
+#include <linux/kprobes.h>
 #include <linux/bootmem.h>
 #include <linux/module.h>
 #include <linux/mm.h>
@@ -44,6 +45,7 @@
 #include <asm/processor.h>
 #include <asm/proto.h>
 #include <asm/msr-index.h>
+#include <asm/traps.h>
 #include <asm/setup.h>
 #include <asm/desc.h>
 #include <asm/pgtable.h>
@@ -428,11 +430,26 @@ static void xen_write_ldt_entry(struct desc_struct *dt, int entrynum,
 static int cvt_gate_to_trap(int vector, const gate_desc *val,
                             struct trap_info *info)
 {
+        unsigned long addr;
+
         if (val->type != GATE_TRAP && val->type != GATE_INTERRUPT)
                 return 0;
 
         info->vector = vector;
-        info->address = gate_offset(*val);
+
+        addr = gate_offset(*val);
+#ifdef CONFIG_X86_64
+        if (addr == (unsigned long)debug)
+                addr = (unsigned long)xen_debug;
+        else if (addr == (unsigned long)int3)
+                addr = (unsigned long)xen_int3;
+        else if (addr == (unsigned long)stack_segment)
+                addr = (unsigned long)xen_stack_segment;
+        else
+                WARN_ON(val->ist != 0);
+#endif  /* CONFIG_X86_64 */
+        info->address = addr;
+
         info->cs = gate_segment(*val);
         info->flags = val->dpl;
         /* interrupt gates clear IF */