[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 <bstroesser@fujitsu-siemens.com>
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 471 insertions, 35 deletions

diff --git a/arch/um/sys-i386/ldt.c b/arch/um/sys-i386/ldt.c
index 36b5c2c13289..6360f1c958d0 100644
--- a/arch/um/sys-i386/ldt.c
+++ b/arch/um/sys-i386/ldt.c
@@ -3,53 +3,26 @@
  * Licensed under the GPL
  */
 
+#include "linux/stddef.h"
 #include "linux/config.h"
 #include "linux/sched.h"
 #include "linux/slab.h"
 #include "linux/types.h"
+#include "linux/errno.h"
 #include "asm/uaccess.h"
-#include "asm/ptrace.h"
 #include "asm/smp.h"
 #include "asm/ldt.h"
+#include "asm/unistd.h"
 #include "choose-mode.h"
 #include "kern.h"
 #include "mode_kern.h"
 
-#ifdef CONFIG_MODE_TT
-
 extern int modify_ldt(int func, void *ptr, unsigned long bytecount);
 
-static int do_modify_ldt_tt(int func, void *ptr, unsigned long bytecount)
-{
-        return modify_ldt(func, ptr, bytecount);
-}
-
-#endif
-
-#ifdef CONFIG_MODE_SKAS
-
-#include "skas.h"
-#include "skas_ptrace.h"
-
-static int do_modify_ldt_skas(int func, void *ptr, unsigned long bytecount)
-{
-        struct ptrace_ldt ldt;
-        u32 cpu;
-        int res;
-
-        ldt = ((struct ptrace_ldt) { .func      = func,
-                                     .ptr       = ptr,
-                                     .bytecount = bytecount });
-
-        cpu = get_cpu();
-        res = ptrace(PTRACE_LDT, userspace_pid[cpu], 0, (unsigned long) &ldt);
-        put_cpu();
-
-        return res;
-}
-#endif
+#ifdef CONFIG_MODE_TT
 
-int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount)
+static long do_modify_ldt_tt(int func, void __user *ptr,
+                              unsigned long bytecount)
 {
         struct user_desc info;
         int res = 0;
@@ -89,8 +62,7 @@ int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount)
                 goto out;
         }
 
-        res = CHOOSE_MODE_PROC(do_modify_ldt_tt, do_modify_ldt_skas, func,
-                                p, bytecount);
+        res = modify_ldt(func, p, bytecount);
         if(res < 0)
                 goto out;
 
@@ -108,3 +80,467 @@ out:
         kfree(buf);
         return res;
 }
+
+#endif
+
+#ifdef CONFIG_MODE_SKAS
+
+#include "skas.h"
+#include "skas_ptrace.h"
+#include "asm/mmu_context.h"
+
+long write_ldt_entry(struct mm_id * mm_idp, int func, struct user_desc * desc,
+                     void **addr, int done)
+{
+        long res;
+
+        if(proc_mm){
+                /* This is a special handling for the case, that the mm to
+                 * modify isn't current->active_mm.
+                 * If this is called directly by modify_ldt,
+                 *     (current->active_mm->context.skas.u == mm_idp)
+                 * will be true. So no call to switch_mm_skas(mm_idp) is done.
+                 * If this is called in case of init_new_ldt or PTRACE_LDT,
+                 * mm_idp won't belong to current->active_mm, but child->mm.
+                 * So we need to switch child's mm into our userspace, then
+                 * later switch back.
+                 *
+                 * Note: I'm unshure: should interrupts be disabled here?
+                 */
+                if(!current->active_mm || current->active_mm == &init_mm ||
+                   mm_idp != &current->active_mm->context.skas.id)
+                        switch_mm_skas(mm_idp);
+        }
+
+        if(ptrace_ldt) {
+                struct ptrace_ldt ldt_op = (struct ptrace_ldt) {
+                        .func = func,
+                        .ptr = desc,
+                        .bytecount = sizeof(*desc)};
+                u32 cpu;
+                int pid;
+
+                if(!proc_mm)
+                        pid = mm_idp->u.pid;
+                else {
+                        cpu = get_cpu();
+                        pid = userspace_pid[cpu];
+                }
+
+                res = ptrace(PTRACE_LDT, pid, 0, (unsigned long) &ldt_op);
+                if(res)
+                        res = errno;
+
+                if(proc_mm)
+                        put_cpu();
+        }
+        else {
+                void *stub_addr;
+                res = syscall_stub_data(mm_idp, (unsigned long *)desc,
+                                        (sizeof(*desc) + sizeof(long) - 1) &
+                                            ~(sizeof(long) - 1),
+                                        addr, &stub_addr);
+                if(!res){
+                        unsigned long args[] = { func,
+                                                 (unsigned long)stub_addr,
+                                                 sizeof(*desc),
+                                                 0, 0, 0 };
+                        res = run_syscall_stub(mm_idp, __NR_modify_ldt, args,
+                                               0, addr, done);
+                }
+        }
+
+        if(proc_mm){
+                /* This is the second part of special handling, that makes
+                 * PTRACE_LDT possible to implement.
+                 */
+                if(current->active_mm && current->active_mm != &init_mm &&
+                   mm_idp != &current->active_mm->context.skas.id)
+                        switch_mm_skas(&current->active_mm->context.skas.id);
+        }
+
+        return res;
+}
+
+static long read_ldt_from_host(void __user * ptr, unsigned long bytecount)
+{
+        int res, n;
+        struct ptrace_ldt ptrace_ldt = (struct ptrace_ldt) {
+                        .func = 0,
+                        .bytecount = bytecount,
+                        .ptr = (void *)kmalloc(bytecount, GFP_KERNEL)};
+        u32 cpu;
+
+        if(ptrace_ldt.ptr == NULL)
+                return -ENOMEM;
+
+        /* This is called from sys_modify_ldt only, so userspace_pid gives
+         * us the right number
+         */
+
+        cpu = get_cpu();
+        res = ptrace(PTRACE_LDT, userspace_pid[cpu], 0,
+                     (unsigned long) &ptrace_ldt);
+        put_cpu();
+        if(res < 0)
+                goto out;
+
+        n = copy_to_user(ptr, ptrace_ldt.ptr, res);
+        if(n != 0)
+                res = -EFAULT;
+
+  out:
+        kfree(ptrace_ldt.ptr);
+
+        return res;
+}
+
+/*
+ * In skas mode, we hold our own ldt data in UML.
+ * Thus, the code implementing sys_modify_ldt_skas
+ * is very similar to (and mostly stolen from) sys_modify_ldt
+ * for arch/i386/kernel/ldt.c
+ * The routines copied and modified in part are:
+ * - read_ldt
+ * - read_default_ldt
+ * - write_ldt
+ * - sys_modify_ldt_skas
+ */
+
+static int read_ldt(void __user * ptr, unsigned long bytecount)
+{
+        int i, err = 0;
+        unsigned long size;
+        uml_ldt_t * ldt = &current->mm->context.skas.ldt;
+
+        if(!ldt->entry_count)
+                goto out;
+        if(bytecount > LDT_ENTRY_SIZE*LDT_ENTRIES)
+                bytecount = LDT_ENTRY_SIZE*LDT_ENTRIES;
+        err = bytecount;
+
+        if(ptrace_ldt){
+                return read_ldt_from_host(ptr, bytecount);
+        }
+
+        down(&ldt->semaphore);
+        if(ldt->entry_count <= LDT_DIRECT_ENTRIES){
+                size = LDT_ENTRY_SIZE*LDT_DIRECT_ENTRIES;
+                if(size > bytecount)
+                        size = bytecount;
+                if(copy_to_user(ptr, ldt->entries, size))
+                        err = -EFAULT;
+                bytecount -= size;
+                ptr += size;
+        }
+        else {
+                for(i=0; i<ldt->entry_count/LDT_ENTRIES_PER_PAGE && bytecount;
+                         i++){
+                        size = PAGE_SIZE;
+                        if(size > bytecount)
+                                size = bytecount;
+                        if(copy_to_user(ptr, ldt->pages[i], size)){
+                                err = -EFAULT;
+                                break;
+                        }
+                        bytecount -= size;
+                        ptr += size;
+                }
+        }
+        up(&ldt->semaphore);
+
+        if(bytecount == 0 || err == -EFAULT)
+                goto out;
+
+        if(clear_user(ptr, bytecount))
+                err = -EFAULT;
+
+out:
+        return err;
+}
+
+static int read_default_ldt(void __user * ptr, unsigned long bytecount)
+{
+        int err;
+
+        if(bytecount > 5*LDT_ENTRY_SIZE)
+                bytecount = 5*LDT_ENTRY_SIZE;
+
+        err = bytecount;
+        /* UML doesn't support lcall7 and lcall27.
+         * So, we don't really have a default ldt, but emulate
+         * an empty ldt of common host default ldt size.
+         */
+        if(clear_user(ptr, bytecount))
+                err = -EFAULT;
+
+        return err;
+}
+
+static int write_ldt(void __user * ptr, unsigned long bytecount, int func)
+{
+        uml_ldt_t * ldt = &current->mm->context.skas.ldt;
+        struct mm_id * mm_idp = &current->mm->context.skas.id;
+        int i, err;
+        struct user_desc ldt_info;
+        struct ldt_entry entry0, *ldt_p;
+        void *addr = NULL;
+
+        err = -EINVAL;
+        if(bytecount != sizeof(ldt_info))
+                goto out;
+        err = -EFAULT;
+        if(copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
+                goto out;
+
+        err = -EINVAL;
+        if(ldt_info.entry_number >= LDT_ENTRIES)
+                goto out;
+        if(ldt_info.contents == 3){
+                if (func == 1)
+                        goto out;
+                if (ldt_info.seg_not_present == 0)
+                        goto out;
+        }
+
+        if(!ptrace_ldt)
+                down(&ldt->semaphore);
+
+        err = write_ldt_entry(mm_idp, func, &ldt_info, &addr, 1);
+        if(err)
+                goto out_unlock;
+        else if(ptrace_ldt) {
+        /* With PTRACE_LDT available, this is used as a flag only */
+                ldt->entry_count = 1;
+                goto out;
+        }
+
+        if(ldt_info.entry_number >= ldt->entry_count &&
+           ldt_info.entry_number >= LDT_DIRECT_ENTRIES){
+                for(i=ldt->entry_count/LDT_ENTRIES_PER_PAGE;
+                    i*LDT_ENTRIES_PER_PAGE <= ldt_info.entry_number;
+                    i++){
+                        if(i == 0)
+                                memcpy(&entry0, ldt->entries, sizeof(entry0));
+                        ldt->pages[i] = (struct ldt_entry *)
+                                        __get_free_page(GFP_KERNEL|__GFP_ZERO);
+                        if(!ldt->pages[i]){
+                                err = -ENOMEM;
+                                /* Undo the change in host */
+                                memset(&ldt_info, 0, sizeof(ldt_info));
+                                write_ldt_entry(mm_idp, 1, &ldt_info, &addr, 1);
+                                goto out_unlock;
+                        }
+                        if(i == 0) {
+                                memcpy(ldt->pages[0], &entry0, sizeof(entry0));
+                                memcpy(ldt->pages[0]+1, ldt->entries+1,
+                                       sizeof(entry0)*(LDT_DIRECT_ENTRIES-1));
+                        }
+                        ldt->entry_count = (i + 1) * LDT_ENTRIES_PER_PAGE;
+                }
+        }
+        if(ldt->entry_count <= ldt_info.entry_number)
+                ldt->entry_count = ldt_info.entry_number + 1;
+
+        if(ldt->entry_count <= LDT_DIRECT_ENTRIES)
+                ldt_p = ldt->entries + ldt_info.entry_number;
+        else
+                ldt_p = ldt->pages[ldt_info.entry_number/LDT_ENTRIES_PER_PAGE] +
+                        ldt_info.entry_number%LDT_ENTRIES_PER_PAGE;
+
+        if(ldt_info.base_addr == 0 && ldt_info.limit == 0 &&
+           (func == 1 || LDT_empty(&ldt_info))){
+                ldt_p->a = 0;
+                ldt_p->b = 0;
+        }
+        else{
+                if (func == 1)
+                        ldt_info.useable = 0;
+                ldt_p->a = LDT_entry_a(&ldt_info);
+                ldt_p->b = LDT_entry_b(&ldt_info);
+        }
+        err = 0;
+
+out_unlock:
+        up(&ldt->semaphore);
+out:
+        return err;
+}
+
+static long do_modify_ldt_skas(int func, void __user *ptr,
+                               unsigned long bytecount)
+{
+        int ret = -ENOSYS;
+
+        switch (func) {
+                case 0:
+                        ret = read_ldt(ptr, bytecount);
+                        break;
+                case 1:
+                case 0x11:
+                        ret = write_ldt(ptr, bytecount, func);
+                        break;
+                case 2:
+                        ret = read_default_ldt(ptr, bytecount);
+                        break;
+        }
+        return ret;
+}
+
+short dummy_list[9] = {0, -1};
+short * host_ldt_entries = NULL;
+
+void ldt_get_host_info(void)
+{
+        long ret;
+        struct ldt_entry * ldt;
+        int i, size, k, order;
+
+        host_ldt_entries = dummy_list+1;
+
+        for(i = LDT_PAGES_MAX-1, order=0; i; i>>=1, order++);
+
+        ldt = (struct ldt_entry *)
+              __get_free_pages(GFP_KERNEL|__GFP_ZERO, order);
+        if(ldt == NULL) {
+                printk("ldt_get_host_info: couldn't allocate buffer for host ldt\n");
+                return;
+        }
+
+        ret = modify_ldt(0, ldt, (1<<order)*PAGE_SIZE);
+        if(ret < 0) {
+                printk("ldt_get_host_info: couldn't read host ldt\n");
+                goto out_free;
+        }
+        if(ret == 0) {
+                /* default_ldt is active, simply write an empty entry 0 */
+                host_ldt_entries = dummy_list;
+                goto out_free;
+        }
+
+        for(i=0, size=0; i<ret/LDT_ENTRY_SIZE; i++){
+                if(ldt[i].a != 0 || ldt[i].b != 0)
+                        size++;
+        }
+
+        if(size < sizeof(dummy_list)/sizeof(dummy_list[0])) {
+                host_ldt_entries = dummy_list;
+        }
+        else {
+                size = (size + 1) * sizeof(dummy_list[0]);
+                host_ldt_entries = (short *)kmalloc(size, GFP_KERNEL);
+                if(host_ldt_entries == NULL) {
+                        printk("ldt_get_host_info: couldn't allocate host ldt list\n");
+                        goto out_free;
+                }
+        }
+
+        for(i=0, k=0; i<ret/LDT_ENTRY_SIZE; i++){
+                if(ldt[i].a != 0 || ldt[i].b != 0) {
+                        host_ldt_entries[k++] = i;
+                }
+        }
+        host_ldt_entries[k] = -1;
+
+out_free:
+        free_pages((unsigned long)ldt, order);
+}
+
+long init_new_ldt(struct mmu_context_skas * new_mm,
+                  struct mmu_context_skas * from_mm)
+{
+        struct user_desc desc;
+        short * num_p;
+        int i;
+        long page, err=0;
+        void *addr = NULL;
+
+        memset(&desc, 0, sizeof(desc));
+
+        if(!ptrace_ldt)
+                init_MUTEX(&new_mm->ldt.semaphore);
+
+        if(!from_mm){
+                /*
+                 * We have to initialize a clean ldt.
+                 */
+                if(proc_mm) {
+                        /*
+                         * If the new mm was created using proc_mm, host's
+                         * default-ldt currently is assigned, which normally
+                         * contains the call-gates for lcall7 and lcall27.
+                         * To remove these gates, we simply write an empty
+                         * entry as number 0 to the host.
+                         */
+                        err = write_ldt_entry(&new_mm->id, 1, &desc,
+                                              &addr, 1);
+                }
+                else{
+                        /*
+                         * Now we try to retrieve info about the ldt, we
+                         * inherited from the host. All ldt-entries found
+                         * will be reset in the following loop
+                         */
+                        if(host_ldt_entries == NULL)
+                                ldt_get_host_info();
+                        for(num_p=host_ldt_entries; *num_p != -1; num_p++){
+                                desc.entry_number = *num_p;
+                                err = write_ldt_entry(&new_mm->id, 1, &desc,
+                                                      &addr, *(num_p + 1) == -1);
+                                if(err)
+                                        break;
+                        }
+                }
+                new_mm->ldt.entry_count = 0;
+        }
+        else if (!ptrace_ldt) {
+                /* Our local LDT is used to supply the data for
+                 * modify_ldt(READLDT), if PTRACE_LDT isn't available,
+                 * i.e., we have to use the stub for modify_ldt, which
+                 * can't handle the big read buffer of up to 64kB.
+                 */
+                down(&from_mm->ldt.semaphore);
+                if(from_mm->ldt.entry_count <= LDT_DIRECT_ENTRIES){
+                        memcpy(new_mm->ldt.entries, from_mm->ldt.entries,
+                               sizeof(new_mm->ldt.entries));
+                }
+                else{
+                        i = from_mm->ldt.entry_count / LDT_ENTRIES_PER_PAGE;
+                        while(i-->0){
+                                page = __get_free_page(GFP_KERNEL|__GFP_ZERO);
+                                if (!page){
+                                        err = -ENOMEM;
+                                        break;
+                                }
+                                new_mm->ldt.pages[i] = (struct ldt_entry*)page;
+                                memcpy(new_mm->ldt.pages[i],
+                                       from_mm->ldt.pages[i], PAGE_SIZE);
+                        }
+                }
+                new_mm->ldt.entry_count = from_mm->ldt.entry_count;
+                up(&from_mm->ldt.semaphore);
+        }
+
+        return err;
+}
+
+
+void free_ldt(struct mmu_context_skas * mm)
+{
+        int i;
+
+        if(!ptrace_ldt && mm->ldt.entry_count > LDT_DIRECT_ENTRIES){
+                i = mm->ldt.entry_count / LDT_ENTRIES_PER_PAGE;
+                while(i-- > 0){
+                        free_page((long )mm->ldt.pages[i]);
+                }
+        }
+        mm->ldt.entry_count = 0;
+}
+#endif
+
+int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount)
+{
+        return(CHOOSE_MODE_PROC(do_modify_ldt_tt, do_modify_ldt_skas, func,
+                                ptr, bytecount));
+}