x86/um/ldt.c

0001 /*
0002  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
0003  * Licensed under the GPL
0004  */
0005
0006 #include <linux/mm.h>
0007 #include <linux/sched.h>
0008 #include <linux/slab.h>
0009 #include <linux/syscalls.h>
0010 #include <linux/uaccess.h>
0011 #include <asm/unistd.h>
0012 #include <os.h>
0013 #include <skas.h>
0014 #include <sysdep/tls.h>
0015
0016 static inline int modify_ldt (int func, void *ptr, unsigned long bytecount)
0017 {
0018     return syscall(__NR_modify_ldt, func, ptr, bytecount);
0019 }
0020
0021 static long write_ldt_entry(struct mm_id *mm_idp, int func,
0022              struct user_desc *desc, void **addr, int done)
0023 {
0024     long res;
0025     void *stub_addr;
0026
0027     BUILD_BUG_ON(sizeof(*desc) % sizeof(long));
0028
0029     res = syscall_stub_data(mm_idp, (unsigned long *)desc,
0030                 sizeof(*desc) / sizeof(long),
0031                 addr, &stub_addr);
0032     if (!res) {
0033         unsigned long args[] = { func,
0034                      (unsigned long)stub_addr,
0035                      sizeof(*desc),
0036                      0, 0, 0 };
0037         res = run_syscall_stub(mm_idp, __NR_modify_ldt, args,
0038                        0, addr, done);
0039     }
0040
0041     return res;
0042 }
0043
0044 /*
0045  * In skas mode, we hold our own ldt data in UML.
0046  * Thus, the code implementing sys_modify_ldt_skas
0047  * is very similar to (and mostly stolen from) sys_modify_ldt
0048  * for arch/i386/kernel/ldt.c
0049  * The routines copied and modified in part are:
0050  * - read_ldt
0051  * - read_default_ldt
0052  * - write_ldt
0053  * - sys_modify_ldt_skas
0054  */
0055
0056 static int read_ldt(void __user * ptr, unsigned long bytecount)
0057 {
0058     int i, err = 0;
0059     unsigned long size;
0060     uml_ldt_t *ldt = &current->mm->context.arch.ldt;
0061
0062     if (!ldt->entry_count)
0063         goto out;
0064     if (bytecount > LDT_ENTRY_SIZE*LDT_ENTRIES)
0065         bytecount = LDT_ENTRY_SIZE*LDT_ENTRIES;
0066     err = bytecount;
0067
0068     mutex_lock(&ldt->lock);
0069     if (ldt->entry_count <= LDT_DIRECT_ENTRIES) {
0070         size = LDT_ENTRY_SIZE*LDT_DIRECT_ENTRIES;
0071         if (size > bytecount)
0072             size = bytecount;
0073         if (copy_to_user(ptr, ldt->u.entries, size))
0074             err = -EFAULT;
0075         bytecount -= size;
0076         ptr += size;
0077     }
0078     else {
0079         for (i=0; i<ldt->entry_count/LDT_ENTRIES_PER_PAGE && bytecount;
0080              i++) {
0081             size = PAGE_SIZE;
0082             if (size > bytecount)
0083                 size = bytecount;
0084             if (copy_to_user(ptr, ldt->u.pages[i], size)) {
0085                 err = -EFAULT;
0086                 break;
0087             }
0088             bytecount -= size;
0089             ptr += size;
0090         }
0091     }
0092     mutex_unlock(&ldt->lock);
0093
0094     if (bytecount == 0 || err == -EFAULT)
0095         goto out;
0096
0097     if (clear_user(ptr, bytecount))
0098         err = -EFAULT;
0099
0100 out:
0101     return err;
0102 }
0103
0104 static int read_default_ldt(void __user * ptr, unsigned long bytecount)
0105 {
0106     int err;
0107
0108     if (bytecount > 5*LDT_ENTRY_SIZE)
0109         bytecount = 5*LDT_ENTRY_SIZE;
0110
0111     err = bytecount;
0112     /*
0113      * UML doesn't support lcall7 and lcall27.
0114      * So, we don't really have a default ldt, but emulate
0115      * an empty ldt of common host default ldt size.
0116      */
0117     if (clear_user(ptr, bytecount))
0118         err = -EFAULT;
0119
0120     return err;
0121 }
0122
0123 static int write_ldt(void __user * ptr, unsigned long bytecount, int func)
0124 {
0125     uml_ldt_t *ldt = &current->mm->context.arch.ldt;
0126     struct mm_id * mm_idp = &current->mm->context.id;
0127     int i, err;
0128     struct user_desc ldt_info;
0129     struct ldt_entry entry0, *ldt_p;
0130     void *addr = NULL;
0131
0132     err = -EINVAL;
0133     if (bytecount != sizeof(ldt_info))
0134         goto out;
0135     err = -EFAULT;
0136     if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
0137         goto out;
0138
0139     err = -EINVAL;
0140     if (ldt_info.entry_number >= LDT_ENTRIES)
0141         goto out;
0142     if (ldt_info.contents == 3) {
0143         if (func == 1)
0144             goto out;
0145         if (ldt_info.seg_not_present == 0)
0146             goto out;
0147     }
0148
0149     mutex_lock(&ldt->lock);
0150
0151     err = write_ldt_entry(mm_idp, func, &ldt_info, &addr, 1);
0152     if (err)
0153         goto out_unlock;
0154
0155     if (ldt_info.entry_number >= ldt->entry_count &&
0156         ldt_info.entry_number >= LDT_DIRECT_ENTRIES) {
0157         for (i=ldt->entry_count/LDT_ENTRIES_PER_PAGE;
0158              i*LDT_ENTRIES_PER_PAGE <= ldt_info.entry_number;
0159              i++) {
0160             if (i == 0)
0161                 memcpy(&entry0, ldt->u.entries,
0162                        sizeof(entry0));
0163             ldt->u.pages[i] = (struct ldt_entry *)
0164                 __get_free_page(GFP_KERNEL|__GFP_ZERO);
0165             if (!ldt->u.pages[i]) {
0166                 err = -ENOMEM;
0167                 /* Undo the change in host */
0168                 memset(&ldt_info, 0, sizeof(ldt_info));
0169                 write_ldt_entry(mm_idp, 1, &ldt_info, &addr, 1);
0170                 goto out_unlock;
0171             }
0172             if (i == 0) {
0173                 memcpy(ldt->u.pages[0], &entry0,
0174                        sizeof(entry0));
0175                 memcpy(ldt->u.pages[0]+1, ldt->u.entries+1,
0176                        sizeof(entry0)*(LDT_DIRECT_ENTRIES-1));
0177             }
0178             ldt->entry_count = (i + 1) * LDT_ENTRIES_PER_PAGE;
0179         }
0180     }
0181     if (ldt->entry_count <= ldt_info.entry_number)
0182         ldt->entry_count = ldt_info.entry_number + 1;
0183
0184     if (ldt->entry_count <= LDT_DIRECT_ENTRIES)
0185         ldt_p = ldt->u.entries + ldt_info.entry_number;
0186     else
0187         ldt_p = ldt->u.pages[ldt_info.entry_number/LDT_ENTRIES_PER_PAGE] +
0188             ldt_info.entry_number%LDT_ENTRIES_PER_PAGE;
0189
0190     if (ldt_info.base_addr == 0 && ldt_info.limit == 0 &&
0191        (func == 1 || LDT_empty(&ldt_info))) {
0192         ldt_p->a = 0;
0193         ldt_p->b = 0;
0194     }
0195     else{
0196         if (func == 1)
0197             ldt_info.useable = 0;
0198         ldt_p->a = LDT_entry_a(&ldt_info);
0199         ldt_p->b = LDT_entry_b(&ldt_info);
0200     }
0201     err = 0;
0202
0203 out_unlock:
0204     mutex_unlock(&ldt->lock);
0205 out:
0206     return err;
0207 }
0208
0209 static long do_modify_ldt_skas(int func, void __user *ptr,
0210                    unsigned long bytecount)
0211 {
0212     int ret = -ENOSYS;
0213
0214     switch (func) {
0215         case 0:
0216             ret = read_ldt(ptr, bytecount);
0217             break;
0218         case 1:
0219         case 0x11:
0220             ret = write_ldt(ptr, bytecount, func);
0221             break;
0222         case 2:
0223             ret = read_default_ldt(ptr, bytecount);
0224             break;
0225     }
0226     return ret;
0227 }
0228
0229 static DEFINE_SPINLOCK(host_ldt_lock);
0230 static short dummy_list[9] = {0, -1};
0231 static short * host_ldt_entries = NULL;
0232
0233 static void ldt_get_host_info(void)
0234 {
0235     long ret;
0236     struct ldt_entry * ldt;
0237     short *tmp;
0238     int i, size, k, order;
0239
0240     spin_lock(&host_ldt_lock);
0241
0242     if (host_ldt_entries != NULL) {
0243         spin_unlock(&host_ldt_lock);
0244         return;
0245     }
0246     host_ldt_entries = dummy_list+1;
0247
0248     spin_unlock(&host_ldt_lock);
0249
0250     for (i = LDT_PAGES_MAX-1, order=0; i; i>>=1, order++)
0251         ;
0252
0253     ldt = (struct ldt_entry *)
0254           __get_free_pages(GFP_KERNEL|__GFP_ZERO, order);
0255     if (ldt == NULL) {
0256         printk(KERN_ERR "ldt_get_host_info: couldn't allocate buffer "
0257                "for host ldt\n");
0258         return;
0259     }
0260
0261     ret = modify_ldt(0, ldt, (1<<order)*PAGE_SIZE);
0262     if (ret < 0) {
0263         printk(KERN_ERR "ldt_get_host_info: couldn't read host ldt\n");
0264         goto out_free;
0265     }
0266     if (ret == 0) {
0267         /* default_ldt is active, simply write an empty entry 0 */
0268         host_ldt_entries = dummy_list;
0269         goto out_free;
0270     }
0271
0272     for (i=0, size=0; i<ret/LDT_ENTRY_SIZE; i++) {
0273         if (ldt[i].a != 0 || ldt[i].b != 0)
0274             size++;
0275     }
0276
0277     if (size < ARRAY_SIZE(dummy_list))
0278         host_ldt_entries = dummy_list;
0279     else {
0280         size = (size + 1) * sizeof(dummy_list[0]);
0281         tmp = kmalloc(size, GFP_KERNEL);
0282         if (tmp == NULL) {
0283             printk(KERN_ERR "ldt_get_host_info: couldn't allocate "
0284                    "host ldt list\n");
0285             goto out_free;
0286         }
0287         host_ldt_entries = tmp;
0288     }
0289
0290     for (i=0, k=0; i<ret/LDT_ENTRY_SIZE; i++) {
0291         if (ldt[i].a != 0 || ldt[i].b != 0)
0292             host_ldt_entries[k++] = i;
0293     }
0294     host_ldt_entries[k] = -1;
0295
0296 out_free:
0297     free_pages((unsigned long)ldt, order);
0298 }
0299
0300 long init_new_ldt(struct mm_context *new_mm, struct mm_context *from_mm)
0301 {
0302     struct user_desc desc;
0303     short * num_p;
0304     int i;
0305     long page, err=0;
0306     void *addr = NULL;
0307
0308
0309     mutex_init(&new_mm->arch.ldt.lock);
0310
0311     if (!from_mm) {
0312         memset(&desc, 0, sizeof(desc));
0313         /*
0314          * Now we try to retrieve info about the ldt, we
0315          * inherited from the host. All ldt-entries found
0316          * will be reset in the following loop
0317          */
0318         ldt_get_host_info();
0319         for (num_p=host_ldt_entries; *num_p != -1; num_p++) {
0320             desc.entry_number = *num_p;
0321             err = write_ldt_entry(&new_mm->id, 1, &desc,
0322                           &addr, *(num_p + 1) == -1);
0323             if (err)
0324                 break;
0325         }
0326         new_mm->arch.ldt.entry_count = 0;
0327
0328         goto out;
0329     }
0330
0331     /*
0332      * Our local LDT is used to supply the data for
0333      * modify_ldt(READLDT), if PTRACE_LDT isn't available,
0334      * i.e., we have to use the stub for modify_ldt, which
0335      * can't handle the big read buffer of up to 64kB.
0336      */
0337     mutex_lock(&from_mm->arch.ldt.lock);
0338     if (from_mm->arch.ldt.entry_count <= LDT_DIRECT_ENTRIES)
0339         memcpy(new_mm->arch.ldt.u.entries, from_mm->arch.ldt.u.entries,
0340                sizeof(new_mm->arch.ldt.u.entries));
0341     else {
0342         i = from_mm->arch.ldt.entry_count / LDT_ENTRIES_PER_PAGE;
0343         while (i-->0) {
0344             page = __get_free_page(GFP_KERNEL|__GFP_ZERO);
0345             if (!page) {
0346                 err = -ENOMEM;
0347                 break;
0348             }
0349             new_mm->arch.ldt.u.pages[i] =
0350                 (struct ldt_entry *) page;
0351             memcpy(new_mm->arch.ldt.u.pages[i],
0352                    from_mm->arch.ldt.u.pages[i], PAGE_SIZE);
0353         }
0354     }
0355     new_mm->arch.ldt.entry_count = from_mm->arch.ldt.entry_count;
0356     mutex_unlock(&from_mm->arch.ldt.lock);
0357
0358     out:
0359     return err;
0360 }
0361
0362
0363 void free_ldt(struct mm_context *mm)
0364 {
0365     int i;
0366
0367     if (mm->arch.ldt.entry_count > LDT_DIRECT_ENTRIES) {
0368         i = mm->arch.ldt.entry_count / LDT_ENTRIES_PER_PAGE;
0369         while (i-- > 0)
0370             free_page((long) mm->arch.ldt.u.pages[i]);
0371     }
0372     mm->arch.ldt.entry_count = 0;
0373 }
0374
0375 SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr ,
0376         unsigned long , bytecount)
0377 {
0378     /* See non-um modify_ldt() for why we do this cast */
0379     return (unsigned int)do_modify_ldt_skas(func, ptr, bytecount);
0380 }