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>

diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
index 0d5342515b8696970ec533572055df8b98ef74a9..c44e5002f2ff425428b1516e836da285c160e9ee 100644 (file)
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -13,6 +13,9 @@ asmlinkage void divide_error(void);
 asmlinkage void debug(void);
 asmlinkage void nmi(void);
 asmlinkage void int3(void);
+asmlinkage void xen_debug(void);
+asmlinkage void xen_int3(void);
+asmlinkage void xen_stack_segment(void);
 asmlinkage void overflow(void);
 asmlinkage void bounds(void);
 asmlinkage void invalid_op(void);

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 38946c6e843388b33fc165779bd7c0aec8e260d7..bb01ce080b80b8cb6b0496d8df6a450c203b4fef 100644 (file)
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1379,6 +1379,11 @@ END(xen_failsafe_callback)
 paranoidzeroentry_ist debug do_debug DEBUG_STACK
 paranoidzeroentry_ist int3 do_int3 DEBUG_STACK
 paranoiderrorentry stack_segment do_stack_segment
+#ifdef CONFIG_XEN
+zeroentry xen_debug do_debug
+zeroentry xen_int3 do_int3
+errorentry xen_stack_segment do_stack_segment
+#endif
 errorentry general_protection do_general_protection
 errorentry page_fault do_page_fault
 #ifdef CONFIG_X86_MCE

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 12a3159333bc0bee41f908112ab536838242c431..7566e13c0cac2ced579a441a5419d220ef1b3000 100644 (file)
--- 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 */