[Patch v3 4/4] DO NOT APPLY: Test code for interesting stack overflows

[Andrew Cooper <andrew.cooper3@citrix.com>]

I do not recommend trying stacktest3 without stack guards - it interacts very
badly between trashing the NMI stack and the NMI watchdog.
---
 xen/arch/x86/traps.c        |   95 +++++++++++++++++++++++++++++++++++++++++++
 xen/arch/x86/x86_64/traps.c |   15 +++++++
 xen/drivers/char/console.c  |    8 ++++
 xen/drivers/char/serial.c   |   12 ++++++
 xen/include/xen/console.h   |    1 +
 xen/include/xen/serial.h    |    1 +
 6 files changed, 132 insertions(+)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 67be3c4..88ae3d4 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -34,6 +34,7 @@
 #include <xen/console.h>
 #include <xen/shutdown.h>
 #include <xen/guest_access.h>
+#include <xen/keyhandler.h>
 #include <asm/regs.h>
 #include <xen/delay.h>
 #include <xen/event.h>
@@ -3762,6 +3763,100 @@ void asm_domain_crash_synchronous(unsigned long addr)
     __domain_crash_synchronous();
 }
 
+static noinline int recursion(int depth)
+{
+    /* junk on stack to fool naive algorithm */
+    volatile unsigned long addr1 = (unsigned long)&do_get_debugreg;
+    volatile unsigned long tsc;
+    volatile unsigned long addr2 = (unsigned long)&do_set_debugreg;
+
+    if ( depth == 0 )
+    {
+        printk("Did you mean recursion()?\n");
+        run_in_exception_handler(show_stack);
+        return 0;
+    }
+    else
+    {
+        int r;
+        rdtscll(tsc);
+        printk("depth %d, addr1 0x%016"PRIx64", addr2 0x%016"PRIx64", tsc %"PRIu64"\n",
+               depth, addr1, addr2, tsc);
+        r = recursion(depth-1);
+        if ( r )
+            printk("done\n"); /* So GCC cant perform tailcall optimisation */
+        return r;
+    }
+}
+
+static void stacktest1(unsigned char key)
+{
+    printk("In %s()\n", __func__);
+    recursion(5);
+}
+
+static void stacktest2(unsigned char key, struct cpu_user_regs * regs)
+{
+    printk("In %s()\n", __func__);
+    recursion(5);
+}
+
+volatile int in_stacktest3 = 0;
+unsigned long saved_sp, saved_ip, saved_flags = 0;
+static void stacktest3(unsigned char key)
+{
+    printk("In %s()\n", __func__);
+
+    local_irq_save(saved_flags);
+    in_stacktest3 = 1;
+
+    /* Hack up an ability to longjump() out of the #DF handler. */
+recover:
+    asm volatile ("mov %%rsp, %0;\n\t"
+                  : "=m"(saved_sp) );
+    saved_ip = (unsigned long)&&recover;
+
+    if ( in_stacktest3 )
+    {
+        printk("Recovery info: sp %p, ip %p\n",
+               _p(saved_sp), _p(saved_ip));
+        recursion(500);
+    }
+    else
+        printk("Recovered from #DF\n");
+
+    local_irq_restore(saved_flags);
+}
+
+static struct keyhandler stacktest_handler[] = {
+    {
+        .irq_callback = 0,
+        .u.fn = stacktest1,
+        .desc = "Xen stack #1 - Recurse a little and see trace."
+    },
+
+    {
+        .irq_callback = 1,
+        .u.irq_fn = stacktest2,
+        .desc = "Xen stack #2 - Recurse a little and see trace in irq."
+    },
+
+    {
+        .irq_callback = 0,
+        .u.fn = stacktest3,
+        .desc = "Xen stack #3 - Cause stack overflow."
+    },
+ };
+
+static int __init initialize_crashtable(void)
+{
+    register_keyhandler('1', &stacktest_handler[0]);
+    register_keyhandler('2', &stacktest_handler[1]);
+    register_keyhandler('3', &stacktest_handler[2]);
+    return 1;
+}
+__initcall(initialize_crashtable);
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/arch/x86/x86_64/traps.c b/xen/arch/x86/x86_64/traps.c
index bcf72b6..a687954 100644
--- a/xen/arch/x86/x86_64/traps.c
+++ b/xen/arch/x86/x86_64/traps.c
@@ -223,6 +223,9 @@ void show_page_walk(unsigned long addr)
            l1_table_offset(addr), l1e_get_intpte(l1e), pfn);
 }
 
+extern volatile int in_stacktest3;
+extern unsigned long saved_sp, saved_ip;
+
 void double_fault(void);
 void do_double_fault(struct cpu_user_regs *regs)
 {
@@ -250,6 +253,18 @@ void do_double_fault(struct cpu_user_regs *regs)
     _show_registers(regs, crs, CTXT_hypervisor, NULL);
     show_stack_overflow(cpu, regs);
 
+    if ( in_stacktest3 )
+    {
+        in_stacktest3 = 0;
+
+        undo_console_force_unlock();
+        preempt_count() = 0;
+        enable_nmis();
+
+        asm volatile ("mov %0, %%rsp; jmp *%1":
+                      : "r" (saved_sp), "r" (saved_ip) : "memory" );
+    }
+
     panic("DOUBLE FAULT -- system shutdown\n");
 }
 
diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 508f845..967fd53 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -803,6 +803,14 @@ void console_force_unlock(void)
     console_start_sync();
 }
 
+void undo_console_force_unlock(void)
+{
+    watchdog_enable();
+    undo_serial_force_unlock(sercon_handle);
+    console_locks_busted = 0;
+    console_end_sync();
+}
+
 void console_start_sync(void)
 {
     atomic_inc(&print_everything);
diff --git a/xen/drivers/char/serial.c b/xen/drivers/char/serial.c
index 9b006f2..79874f1 100644
--- a/xen/drivers/char/serial.c
+++ b/xen/drivers/char/serial.c
@@ -380,6 +380,18 @@ void serial_force_unlock(int handle)
     serial_start_sync(handle);
 }
 
+void undo_serial_force_unlock(int handle)
+{
+    struct serial_port *port;
+
+    if ( handle == -1 )
+        return;
+
+    port = &com[handle & SERHND_IDX];
+
+    serial_end_sync(handle);
+}
+
 void serial_start_sync(int handle)
 {
     struct serial_port *port;
diff --git a/xen/include/xen/console.h b/xen/include/xen/console.h
index cfb07a2..41c96f8 100644
--- a/xen/include/xen/console.h
+++ b/xen/include/xen/console.h
@@ -21,6 +21,7 @@ int console_has(const char *device);
 int fill_console_start_info(struct dom0_vga_console_info *);
 
 void console_force_unlock(void);
+void undo_console_force_unlock(void);
 
 void console_start_sync(void);
 void console_end_sync(void);
diff --git a/xen/include/xen/serial.h b/xen/include/xen/serial.h
index f38c9b7..fbdcad4 100644
--- a/xen/include/xen/serial.h
+++ b/xen/include/xen/serial.h
@@ -123,6 +123,7 @@ char serial_getc(int handle);
 /* Forcibly prevent serial lockup when the system is in a bad way. */
 /* (NB. This also forces an implicit serial_start_sync()). */
 void serial_force_unlock(int handle);
+void undo_serial_force_unlock(int handle);
 
 /* Start/end a synchronous region (temporarily disable interrupt-driven tx). */
 void serial_start_sync(int handle);
-- 
1.7.10.4