[PATCH] uml: increase granularity of host capability checking

This change enables SKAS0/SKAS3 to work with all combinations of /proc/mm and
PTRACE_FAULTINFO being available or not.

Also it changes the initialization of proc_mm and ptrace_faultinfo slightly,
to ease forcing SKAS0 on a patched host.  Forcing UML to run without /proc/mm
or PTRACE_FAULTINFO by cmdline parameter can be implemented with a setup
resetting the related variable.

Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 28 insertions, 24 deletions

diff --git a/arch/um/kernel/skas/mmu.c b/arch/um/kernel/skas/mmu.c
index d232daa42c3..d837223e22a 100644
--- a/arch/um/kernel/skas/mmu.c
+++ b/arch/um/kernel/skas/mmu.c
@@ -77,23 +77,14 @@ int init_new_context_skas(struct task_struct *task, struct mm_struct *mm)
         struct mm_struct *cur_mm = current->mm;
         struct mm_id *cur_mm_id = &cur_mm->context.skas.id;
         struct mm_id *mm_id = &mm->context.skas.id;
-        unsigned long stack;
-        int from, ret;
+        unsigned long stack = 0;
+        int from, ret = -ENOMEM;
 
-        if(proc_mm){
-                if((cur_mm != NULL) && (cur_mm != &init_mm))
-                        from = cur_mm->context.skas.id.u.mm_fd;
-                else from = -1;
+        if(!proc_mm || !ptrace_faultinfo){
+                stack = get_zeroed_page(GFP_KERNEL);
+                if(stack == 0)
+                        goto out;
 
-                ret = new_mm(from);
-                if(ret < 0){
-                        printk("init_new_context_skas - new_mm failed, "
-                               "errno = %d\n", ret);
-                        return ret;
-                }
-                mm_id->u.mm_fd = ret;
-        }
-        else {
                 /* This zeros the entry that pgd_alloc didn't, needed since
                  * we are about to reinitialize it, and want mm.nr_ptes to
                  * be accurate.
@@ -103,20 +94,30 @@ int init_new_context_skas(struct task_struct *task, struct mm_struct *mm)
                 ret = init_stub_pte(mm, CONFIG_STUB_CODE,
                                     (unsigned long) &__syscall_stub_start);
                 if(ret)
-                        goto out;
-
-                ret = -ENOMEM;
-                stack = get_zeroed_page(GFP_KERNEL);
-                if(stack == 0)
-                        goto out;
-                mm_id->stack = stack;
+                        goto out_free;
 
                 ret = init_stub_pte(mm, CONFIG_STUB_DATA, stack);
                 if(ret)
                         goto out_free;
 
                 mm->nr_ptes--;
+        }
+        mm_id->stack = stack;
 
+        if(proc_mm){
+                if((cur_mm != NULL) && (cur_mm != &init_mm))
+                        from = cur_mm_id->u.mm_fd;
+                else from = -1;
+
+                ret = new_mm(from, stack);
+                if(ret < 0){
+                        printk("init_new_context_skas - new_mm failed, "
+                               "errno = %d\n", ret);
+                        goto out_free;
+                }
+                mm_id->u.mm_fd = ret;
+        }
+        else {
                 if((cur_mm != NULL) && (cur_mm != &init_mm))
                         mm_id->u.pid = copy_context_skas0(stack,
                                                           cur_mm_id->u.pid);
@@ -126,7 +127,8 @@ int init_new_context_skas(struct task_struct *task, struct mm_struct *mm)
         return 0;
 
  out_free:
-        free_page(mm_id->stack);
+        if(mm_id->stack != 0)
+                free_page(mm_id->stack);
  out:
         return ret;
 }
@@ -137,8 +139,10 @@ void destroy_context_skas(struct mm_struct *mm)
 
         if(proc_mm)
                 os_close_file(mmu->id.u.mm_fd);
-        else {
+        else
                 os_kill_ptraced_process(mmu->id.u.pid, 1);
+
+        if(!proc_mm || !ptrace_faultinfo){
                 free_page(mmu->id.stack);
                 free_page(mmu->last_page_table);
         }