[Xen-devel] [xen-devel] [Patch v2 2/4] x86/stack: Adjust boundary conditions for printed stacks.

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Move the boundary into current.h along with the other stack manipulation code,
and apply the same bottom boundary to both the frame pointer and non-frame
pointer case.  This will prevent the non-frame pointer case from finding
certainly-spurious values on the stack in the guest_cpu_user_regs section.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Keir Fraser <keir@xxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Tim Deegan <tim@xxxxxxx>

---

Changes since v1:
 * Change printable bottom depending on frame pointers
---
 xen/arch/x86/traps.c          |    9 ++++-----
 xen/include/asm-x86/current.h |   22 ++++++++++++++++++++++
 2 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index b686177..2bcfc7b 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -199,8 +199,9 @@ static void show_guest_stack(struct vcpu *v, struct 
cpu_user_regs *regs)
 static void __show_trace(unsigned long sp, unsigned long __maybe_unused bp)
 {
     unsigned long *stack = (unsigned long *)sp, addr;
+    unsigned long *bottom = (unsigned long *)get_printable_stack_bottom(sp);
 
-    while ( ((long)stack & (STACK_SIZE-BYTES_PER_LONG)) != 0 )
+    while ( stack <= bottom )
     {
         addr = *stack++;
         if ( is_active_kernel_text(addr) )
@@ -216,12 +217,10 @@ static void __show_trace(unsigned long sp, unsigned long 
__maybe_unused bp)
 /* Stack trace from frames in the stack, using frame pointers */
 static void __show_trace(unsigned long sp, unsigned long bp)
 {
-    unsigned long *frame, next, addr, low, high;
+    unsigned long *frame, next, addr;
 
     /* Bounds for range of valid frame pointer. */
-    low  = sp - 2*sizeof(unsigned long);
-    high = (low & ~(STACK_SIZE - 1)) + 
-        (STACK_SIZE - sizeof(struct cpu_info) - 2*sizeof(unsigned long));
+    unsigned long low = sp, high = get_printable_stack_bottom(sp);
 
     /* The initial frame pointer. */
     next = bp;
diff --git a/xen/include/asm-x86/current.h b/xen/include/asm-x86/current.h
index bec4dbe..02da2ec 100644
--- a/xen/include/asm-x86/current.h
+++ b/xen/include/asm-x86/current.h
@@ -50,6 +50,28 @@ static inline struct cpu_info *get_cpu_info(void)
 #define get_stack_bottom()                      \
     ((unsigned long)&get_cpu_info()->guest_cpu_user_regs.es)
 
+/*
+ * Get the bottom-of-stack, as useful for printing stack traces.  This is
+ * similar position as is returned by get_cpu_info(), but works on arbitrary
+ * stack pointer, rather than just the current.
+ *
+ * In the non-frame pointer case, the boundary is exactly at the cpu_info
+ * structure, which prevents the stack trace walker from mis-interpreting
+ * guest register as Xen return addresses.
+ *
+ * For the frame pointer case, the boundary is further adjusted by two words,
+ * as the call out of assembly does not contain a traditional C stack with
+ * frame pointers.
+ */
+#ifdef CONFIG_FRAME_POINTER
+#define get_printable_stack_bottom(sp)          \
+    ((sp & (~(STACK_SIZE-1))) +                 \
+     (STACK_SIZE - sizeof(struct cpu_info) - 2*sizeof(unsigned long)))
+#else
+#define get_printable_stack_bottom(sp)          \
+    ((sp & (~(STACK_SIZE-1))) + (STACK_SIZE - sizeof(struct cpu_info)))
+#endif
+
 #define reset_stack_and_jump(__fn)              \
     __asm__ __volatile__ (                      \
         "mov %0,%%"__OP"sp; jmp %c1"            \
-- 
1.7.10.4


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