[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>

4 files changed, 96 insertions, 34 deletions

diff --git a/arch/um/kernel/skas/include/skas.h b/arch/um/kernel/skas/include/skas.h
index e91064b7e5a0..03c9d99e15e4 100644
--- a/arch/um/kernel/skas/include/skas.h
+++ b/arch/um/kernel/skas/include/skas.h
@@ -33,7 +33,7 @@ extern void *protect(struct mm_id * mm_idp, unsigned long addr,
                      unsigned long len, int r, int w, int x, int done,
                      void *data);
 extern void user_signal(int sig, union uml_pt_regs *regs, int pid);
-extern int new_mm(int from);
+extern int new_mm(int from, unsigned long stack);
 extern int start_userspace(unsigned long stub_stack);
 extern int copy_context_skas0(unsigned long stack, int pid);
 extern void get_skas_faultinfo(int pid, struct faultinfo * fi);
diff --git a/arch/um/kernel/skas/mmu.c b/arch/um/kernel/skas/mmu.c
index d232daa42c31..d837223e22af 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);
         }
diff --git a/arch/um/kernel/skas/process.c b/arch/um/kernel/skas/process.c
index f228f8b54194..5cd0e9929789 100644
--- a/arch/um/kernel/skas/process.c
+++ b/arch/um/kernel/skas/process.c
@@ -138,6 +138,8 @@ static void handle_trap(int pid, union uml_pt_regs *regs, int local_using_sysemu
 }
 
 extern int __syscall_stub_start;
+int stub_code_fd = -1;
+__u64 stub_code_offset;
 
 static int userspace_tramp(void *stack)
 {
@@ -152,31 +154,31 @@ static int userspace_tramp(void *stack)
                 /* This has a pte, but it can't be mapped in with the usual
                  * tlb_flush mechanism because this is part of that mechanism
                  */
-                int fd;
-                __u64 offset;
-
-                fd = phys_mapping(to_phys(&__syscall_stub_start), &offset);
                 addr = mmap64((void *) UML_CONFIG_STUB_CODE, page_size(),
-                              PROT_EXEC, MAP_FIXED | MAP_PRIVATE, fd, offset);
+                              PROT_EXEC, MAP_FIXED | MAP_PRIVATE,
+                              stub_code_fd, stub_code_offset);
                 if(addr == MAP_FAILED){
-                        printk("mapping mmap stub failed, errno = %d\n",
+                        printk("mapping stub code failed, errno = %d\n",
                                errno);
                         exit(1);
                 }
 
                 if(stack != NULL){
+                        int fd;
+                        __u64 offset;
+
                         fd = phys_mapping(to_phys(stack), &offset);
                         addr = mmap((void *) UML_CONFIG_STUB_DATA, page_size(),
                                     PROT_READ | PROT_WRITE,
                                     MAP_FIXED | MAP_SHARED, fd, offset);
                         if(addr == MAP_FAILED){
-                                printk("mapping segfault stack failed, "
+                                printk("mapping stub stack failed, "
                                        "errno = %d\n", errno);
                                 exit(1);
                         }
                 }
         }
-        if(!ptrace_faultinfo && (stack != NULL)){
+        if(!ptrace_faultinfo){
                 unsigned long v = UML_CONFIG_STUB_CODE +
                                   (unsigned long) stub_segv_handler -
                                   (unsigned long) &__syscall_stub_start;
@@ -202,6 +204,10 @@ int start_userspace(unsigned long stub_stack)
         unsigned long sp;
         int pid, status, n, flags;
 
+        if ( stub_code_fd == -1 )
+                stub_code_fd = phys_mapping(to_phys(&__syscall_stub_start),
+                                            &stub_code_offset);
+
         stack = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC,
                      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
         if(stack == MAP_FAILED)
@@ -363,6 +369,53 @@ int copy_context_skas0(unsigned long new_stack, int pid)
         return pid;
 }
 
+/*
+ * This is used only, if proc_mm is available, while PTRACE_FAULTINFO
+ * isn't. Opening /proc/mm creates a new mm_context, which lacks the stub-pages
+ * Thus, we map them using /proc/mm-fd
+ */
+void map_stub_pages(int fd, unsigned long code,
+                    unsigned long data, unsigned long stack)
+{
+        struct proc_mm_op mmop;
+        int n;
+
+        mmop = ((struct proc_mm_op) { .op        = MM_MMAP,
+                                      .u         =
+                                      { .mmap    =
+                                        { .addr    = code,
+                                          .len     = PAGE_SIZE,
+                                          .prot    = PROT_EXEC,
+                                          .flags   = MAP_FIXED | MAP_PRIVATE,
+                                          .fd      = stub_code_fd,
+                                          .offset  = stub_code_offset
+        } } });
+        n = os_write_file(fd, &mmop, sizeof(mmop));
+        if(n != sizeof(mmop))
+                panic("map_stub_pages : /proc/mm map for code failed, "
+                      "err = %d\n", -n);
+
+        if ( stack ) {
+                __u64 map_offset;
+                int map_fd = phys_mapping(to_phys((void *)stack), &map_offset);
+                mmop = ((struct proc_mm_op)
+                                { .op        = MM_MMAP,
+                                  .u         =
+                                  { .mmap    =
+                                    { .addr    = data,
+                                      .len     = PAGE_SIZE,
+                                      .prot    = PROT_READ | PROT_WRITE,
+                                      .flags   = MAP_FIXED | MAP_SHARED,
+                                      .fd      = map_fd,
+                                      .offset  = map_offset
+                } } });
+                n = os_write_file(fd, &mmop, sizeof(mmop));
+                if(n != sizeof(mmop))
+                        panic("map_stub_pages : /proc/mm map for data failed, "
+                              "err = %d\n", -n);
+        }
+}
+
 void new_thread(void *stack, void **switch_buf_ptr, void **fork_buf_ptr,
                 void (*handler)(int))
 {
diff --git a/arch/um/kernel/skas/process_kern.c b/arch/um/kernel/skas/process_kern.c
index cbabab104ac3..3d1b227226e6 100644
--- a/arch/um/kernel/skas/process_kern.c
+++ b/arch/um/kernel/skas/process_kern.c
@@ -129,7 +129,9 @@ int copy_thread_skas(int nr, unsigned long clone_flags, unsigned long sp,
         return(0);
 }
 
-int new_mm(int from)
+extern void map_stub_pages(int fd, unsigned long code,
+                           unsigned long data, unsigned long stack);
+int new_mm(int from, unsigned long stack)
 {
         struct proc_mm_op copy;
         int n, fd;
@@ -148,6 +150,9 @@ int new_mm(int from)
                                "err = %d\n", -n);
         }
 
+        if(!ptrace_faultinfo)
+                map_stub_pages(fd, CONFIG_STUB_CODE, CONFIG_STUB_DATA, stack);
+
         return(fd);
 }