3 files changed, 22 insertions, 10 deletions

diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index 7743d73768df..c632c08cbbdc 100644
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -69,11 +69,22 @@ static __init int map_switcher(void)
                 switcher_page[i] = virt_to_page(addr);
         }
 
+        /* First we check that the Switcher won't overlap the fixmap area at
+         * the top of memory.  It's currently nowhere near, but it could have
+         * very strange effects if it ever happened. */
+        if (SWITCHER_ADDR + (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE > FIXADDR_START){
+                err = -ENOMEM;
+                printk("lguest: mapping switcher would thwack fixmap\n");
+                goto free_pages;
+        }
+
         /* Now we reserve the "virtual memory area" we want: 0xFFC00000
          * (SWITCHER_ADDR).  We might not get it in theory, but in practice
-         * it's worked so far. */
+         * it's worked so far.  The end address needs +1 because __get_vm_area
+         * allocates an extra guard page, so we need space for that. */
         switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
-                                       VM_ALLOC, SWITCHER_ADDR, VMALLOC_END);
+                                     VM_ALLOC, SWITCHER_ADDR, SWITCHER_ADDR
+                                     + (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE);
         if (!switcher_vma) {
                 err = -ENOMEM;
                 printk("lguest: could not map switcher pages high\n");
diff --git a/drivers/lguest/lguest_user.c b/drivers/lguest/lguest_user.c
index 85d42d3d01a9..2221485b0773 100644
--- a/drivers/lguest/lguest_user.c
+++ b/drivers/lguest/lguest_user.c
@@ -241,15 +241,16 @@ static ssize_t write(struct file *file, const char __user *in,
                 cpu = &lg->cpus[cpu_id];
                 if (!cpu)
                         return -EINVAL;
-        }
 
-        /* Once the Guest is dead, all you can do is read() why it died. */
-        if (lg && lg->dead)
-                return -ENOENT;
+                /* Once the Guest is dead, you can only read() why it died. */
+                if (lg->dead)
+                        return -ENOENT;
 
-        /* If you're not the task which owns the Guest, you can only break */
-        if (lg && current != cpu->tsk && req != LHREQ_BREAK)
-                return -EPERM;
+                /* If you're not the task which owns the Guest, all you can do
+                 * is break the Launcher out of running the Guest. */
+                if (current != cpu->tsk && req != LHREQ_BREAK)
+                        return -EPERM;
+        }
 
         switch (req) {
         case LHREQ_INITIALIZE:
diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
index 275f23c2deb4..a7f64a9d67e0 100644
--- a/drivers/lguest/page_tables.c
+++ b/drivers/lguest/page_tables.c
@@ -391,7 +391,7 @@ static unsigned int find_pgdir(struct lguest *lg, unsigned long pgtable)
 {
         unsigned int i;
         for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
-                if (lg->pgdirs[i].gpgdir == pgtable)
+                if (lg->pgdirs[i].pgdir && lg->pgdirs[i].gpgdir == pgtable)
                         break;
         return i;
 }