[PATCH] uml: maintain own LDT entries

Patch imlements full LDT handling in SKAS:
 * UML holds it's own LDT table, used to deliver data on
   modify_ldt(READ)
 * UML disables the default_ldt, inherited from the host (SKAS3)
   or resets LDT entries, set by host's clib and inherited in
   SKAS0
 * A new global variable skas_needs_stub is inserted, that
   can be used to decide, whether stub-pages must be supported
   or not.
 * Uses the syscall-stub to replace missing PTRACE_LDT (therefore,
   write_ldt_entry needs to be modified)

Signed-off-by: Bodo Stroesser <[email protected]>
Signed-off-by: Jeff Dike <[email protected]>
Cc: Paolo Giarrusso <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Bodo Stroesser

arch/um/kernel/skas/include/mmu-skas.h

@@ -8,13 +8,15 @@
 
 #include "linux/config.h"
 #include "mm_id.h"
+#include "asm/ldt.h"
 
 struct mmu_context_skas {
 	struct mm_id id;
         unsigned long last_page_table;
 #ifdef CONFIG_3_LEVEL_PGTABLES
         unsigned long last_pmd;
 #endif
+	uml_ldt_t ldt;
 };
 
 extern void switch_mm_skas(struct mm_id * mm_idp);

arch/um/kernel/skas/include/skas.h

@@ -10,7 +10,8 @@
 #include "sysdep/ptrace.h"
 
 extern int userspace_pid[];
-extern int proc_mm, ptrace_faultinfo;
+extern int proc_mm, ptrace_faultinfo, ptrace_ldt;
+extern int skas_needs_stub;
 
 extern void switch_threads(void *me, void *next);
 extern void thread_wait(void *sw, void *fb);

arch/um/kernel/skas/mem.c

@@ -20,7 +20,7 @@ unsigned long set_task_sizes_skas(int arg, unsigned long *host_size_out,
 	*task_size_out = CONFIG_HOST_TASK_SIZE;
 #else
 	*host_size_out = top;
-	if (proc_mm && ptrace_faultinfo)
+	if (!skas_needs_stub)
 		*task_size_out = top;
 	else *task_size_out = CONFIG_STUB_START & PGDIR_MASK;
 #endif

arch/um/kernel/skas/mmu.c

@@ -15,6 +15,7 @@
 #include "asm/mmu.h"
 #include "asm/pgalloc.h"
 #include "asm/pgtable.h"
+#include "asm/ldt.h"
 #include "os.h"
 #include "skas.h"
 
@@ -74,13 +75,12 @@ static int init_stub_pte(struct mm_struct *mm, unsigned long proc,
 
 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;
+ 	struct mmu_context_skas *from_mm = NULL;
+	struct mmu_context_skas *to_mm = &mm->context.skas;
 	unsigned long stack = 0;
-	int from, ret = -ENOMEM;
+	int from_fd, ret = -ENOMEM;
 
-	if(!proc_mm || !ptrace_faultinfo){
+	if(skas_needs_stub){
 		stack = get_zeroed_page(GFP_KERNEL);
 		if(stack == 0)
 			goto out;
@@ -102,33 +102,43 @@ int init_new_context_skas(struct task_struct *task, struct mm_struct *mm)
 
 		mm->nr_ptes--;
 	}
-	mm_id->stack = stack;
+
+	to_mm->id.stack = stack;
+	if(current->mm != NULL && current->mm != &init_mm)
+		from_mm = &current->mm->context.skas;
 
 	if(proc_mm){
-		if((cur_mm != NULL) && (cur_mm != &init_mm))
-			from = cur_mm_id->u.mm_fd;
-		else from = -1;
+		if(from_mm)
+			from_fd = from_mm->id.u.mm_fd;
+		else from_fd = -1;
 
-		ret = new_mm(from, stack);
+		ret = new_mm(from_fd, 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;
+		to_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);
-		else mm_id->u.pid = start_userspace(stack);
+		if(from_mm)
+			to_mm->id.u.pid = copy_context_skas0(stack,
+							     from_mm->id.u.pid);
+		else to_mm->id.u.pid = start_userspace(stack);
+	}
+
+	ret = init_new_ldt(to_mm, from_mm);
+	if(ret < 0){
+		printk("init_new_context_skas - init_ldt"
+		       " failed, errno = %d\n", ret);
+		goto out_free;
 	}
 
 	return 0;
 
  out_free:
-	if(mm_id->stack != 0)
-		free_page(mm_id->stack);
+	if(to_mm->id.stack != 0)
+		free_page(to_mm->id.stack);
  out:
 	return ret;
 }

arch/um/kernel/skas/process.c

@@ -381,9 +381,9 @@ int copy_context_skas0(unsigned long new_stack, int 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
+ * This is used only, if stub pages are needed, while proc_mm is
+ * availabl. 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)

arch/um/kernel/skas/process_kern.c

@@ -145,7 +145,7 @@ int new_mm(int from, unsigned long stack)
 			       "err = %d\n", -n);
 	}
 
-	if(!ptrace_faultinfo)
+	if(skas_needs_stub)
 		map_stub_pages(fd, CONFIG_STUB_CODE, CONFIG_STUB_DATA, stack);
 
 	return(fd);

arch/um/os-Linux/start_up.c

@@ -135,7 +135,9 @@ static int stop_ptraced_child(int pid, void *stack, int exitcode,
 }
 
 int ptrace_faultinfo = 1;
+int ptrace_ldt = 1;
 int proc_mm = 1;
+int skas_needs_stub = 0;
 
 static int __init skas0_cmd_param(char *str, int* add)
 {
@@ -352,14 +354,26 @@ __uml_setup("noptracefaultinfo", noptracefaultinfo_cmd_param,
 "    it. To support PTRACE_FAULTINFO, the host needs to be patched\n"
 "    using the current skas3 patch.\n\n");
 
+static int __init noptraceldt_cmd_param(char *str, int* add)
+{
+	ptrace_ldt = 0;
+	return 0;
+}
+
+__uml_setup("noptraceldt", noptraceldt_cmd_param,
+"noptraceldt\n"
+"    Turns off usage of PTRACE_LDT, even if host supports it.\n"
+"    To support PTRACE_LDT, the host needs to be patched using\n"
+"    the current skas3 patch.\n\n");
+
 #ifdef UML_CONFIG_MODE_SKAS
-static inline void check_skas3_ptrace_support(void)
+static inline void check_skas3_ptrace_faultinfo(void)
 {
 	struct ptrace_faultinfo fi;
 	void *stack;
 	int pid, n;
 
-	printf("Checking for the skas3 patch in the host...");
+	printf("  - PTRACE_FAULTINFO...");
 	pid = start_ptraced_child(&stack);
 
 	n = ptrace(PTRACE_FAULTINFO, pid, 0, &fi);
@@ -381,9 +395,49 @@ static inline void check_skas3_ptrace_support(void)
 	stop_ptraced_child(pid, stack, 1, 1);
 }
 
-int can_do_skas(void)
+static inline void check_skas3_ptrace_ldt(void)
+{
+#ifdef PTRACE_LDT
+	void *stack;
+	int pid, n;
+	unsigned char ldtbuf[40];
+	struct ptrace_ldt ldt_op = (struct ptrace_ldt) {
+		.func = 2, /* read default ldt */
+		.ptr = ldtbuf,
+		.bytecount = sizeof(ldtbuf)};
+
+	printf("  - PTRACE_LDT...");
+	pid = start_ptraced_child(&stack);
+
+	n = ptrace(PTRACE_LDT, pid, 0, (unsigned long) &ldt_op);
+	if (n < 0) {
+		if(errno == EIO)
+			printf("not found\n");
+		else {
+			perror("not found");
+		}
+		ptrace_ldt = 0;
+	}
+	else {
+		if(ptrace_ldt)
+			printf("found\n");
+		else
+			printf("found, but use is disabled\n");
+	}
+
+	stop_ptraced_child(pid, stack, 1, 1);
+#else
+	/* PTRACE_LDT might be disabled via cmdline option.
+	 * We want to override this, else we might use the stub
+	 * without real need
+	 */
+	ptrace_ldt = 1;
+#endif
+}
+
+static inline void check_skas3_proc_mm(void)
 {
-	printf("Checking for /proc/mm...");
+	printf("  - /proc/mm...");
 	if (os_access("/proc/mm", OS_ACC_W_OK) < 0) {
  		proc_mm = 0;
 		printf("not found\n");
@@ -394,8 +448,19 @@ int can_do_skas(void)
 		else
 			printf("found\n");
 	}
+}
+
+int can_do_skas(void)
+{
+	printf("Checking for the skas3 patch in the host:\n");
+
+	check_skas3_proc_mm();
+	check_skas3_ptrace_faultinfo();
+	check_skas3_ptrace_ldt();
+
+	if(!proc_mm || !ptrace_faultinfo || !ptrace_ldt)
+		skas_needs_stub = 1;
 
-	check_skas3_ptrace_support();
 	return 1;
 }
 #else

arch/um/scripts/Makefile.rules

@@ -26,8 +26,13 @@ define unprofile
 	$(patsubst -pg,,$(patsubst -fprofile-arcs -ftest-coverage,,$(1)))
 endef
 
+# cmd_make_link checks to see if the $(foo-dir) variable starts with a /.  If
+# so, it's considered to be a path relative to $(srcdir) rather than
+# $(srcdir)/arch/$(SUBARCH).  This is because x86_64 wants to get ldt.c from
+# arch/um/sys-i386 rather than arch/i386 like the other borrowed files.  So,
+# it sets $(ldt.c-dir) to /arch/um/sys-i386.
 quiet_cmd_make_link = SYMLINK $@
-cmd_make_link       = ln -sf $(srctree)/arch/$(SUBARCH)/$($(notdir $@)-dir)/$(notdir $@) $@
+cmd_make_link       = rm -f $@; ln -sf $(srctree)$(if $(filter-out /%,$($(notdir $@)-dir)),/arch/$(SUBARCH))/$($(notdir $@)-dir)/$(notdir $@) $@
 
 # this needs to be before the foreach, because targets does not accept
 # complete paths like $(obj)/$(f). To make sure this works, use a := assignment