[xen stable-4.12] x86/traps: fix an off-by-one error

[patchbot@xxxxxxx]

commit 2291b9795e69f4ec34c6a997d66a50a9fa014775
Author:     Hongyan Xia <hongyxia@xxxxxxxxxx>
AuthorDate: Thu May 7 14:57:35 2020 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu May 7 14:57:35 2020 +0200

    x86/traps: fix an off-by-one error
    
    stack++ can go into the next page and unmap_domain_page() will unmap the
    wrong one, causing mapcache and memory corruption. Fix.
    
    Signed-off-by: Hongyan Xia <hongyxia@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: 2e3d87cc734a895ef5b486926274a178836b67a9
    master date: 2020-05-05 16:13:44 +0100
---
 xen/arch/x86/traps.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 6851f9dbab..3241951805 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -230,6 +230,7 @@ static void compat_show_guest_stack(struct vcpu *v,
                                     int debug_stack_lines)
 {
     unsigned int i, *stack, addr, mask = STACK_SIZE;
+    void *stack_page = NULL;
 
     stack = (unsigned int *)(unsigned long)regs->esp;
     printk("Guest stack trace from esp=%08lx:\n ", (unsigned long)stack);
@@ -252,7 +253,7 @@ static void compat_show_guest_stack(struct vcpu *v,
                 break;
         if ( !vcpu )
         {
-            stack = do_page_walk(v, (unsigned long)stack);
+            stack_page = stack = do_page_walk(v, (unsigned long)stack);
             if ( (unsigned long)stack < PAGE_SIZE )
             {
                 printk("Inaccessible guest memory.\n");
@@ -279,11 +280,10 @@ static void compat_show_guest_stack(struct vcpu *v,
         printk(" %08x", addr);
         stack++;
     }
-    if ( mask == PAGE_SIZE )
-    {
-        BUILD_BUG_ON(PAGE_SIZE == STACK_SIZE);
-        unmap_domain_page(stack);
-    }
+
+    if ( stack_page )
+        unmap_domain_page(stack_page);
+
     if ( i == 0 )
         printk("Stack empty.");
     printk("\n");
@@ -294,6 +294,7 @@ static void show_guest_stack(struct vcpu *v, const struct 
cpu_user_regs *regs)
     int i;
     unsigned long *stack, addr;
     unsigned long mask = STACK_SIZE;
+    void *stack_page = NULL;
 
     /* Avoid HVM as we don't know what the stack looks like. */
     if ( is_hvm_vcpu(v) )
@@ -322,7 +323,7 @@ static void show_guest_stack(struct vcpu *v, const struct 
cpu_user_regs *regs)
         vcpu = maddr_get_owner(read_cr3()) == v->domain ? v : NULL;
         if ( !vcpu )
         {
-            stack = do_page_walk(v, (unsigned long)stack);
+            stack_page = stack = do_page_walk(v, (unsigned long)stack);
             if ( (unsigned long)stack < PAGE_SIZE )
             {
                 printk("Inaccessible guest memory.\n");
@@ -349,11 +350,10 @@ static void show_guest_stack(struct vcpu *v, const struct 
cpu_user_regs *regs)
         printk(" %p", _p(addr));
         stack++;
     }
-    if ( mask == PAGE_SIZE )
-    {
-        BUILD_BUG_ON(PAGE_SIZE == STACK_SIZE);
-        unmap_domain_page(stack);
-    }
+
+    if ( stack_page )
+        unmap_domain_page(stack_page);
+
     if ( i == 0 )
         printk("Stack empty.");
     printk("\n");
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.12