1 // SPDX-License-Identifier: GPL-2.0
3 * Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
4 * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
5 * Copyright (C) 2002 Andi Kleen
7 * This handles calls from both 32bit and 64bit mode.
10 #include <linux/errno.h>
11 #include <linux/gfp.h>
12 #include <linux/sched.h>
13 #include <linux/string.h>
15 #include <linux/smp.h>
16 #include <linux/syscalls.h>
17 #include <linux/slab.h>
18 #include <linux/vmalloc.h>
19 #include <linux/uaccess.h>
23 #include <asm/mmu_context.h>
24 #include <asm/syscalls.h>
26 static void refresh_ldt_segments(void)
32 * Make sure that the cached DS and ES descriptors match the updated
36 if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT)
40 if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT)
45 /* context.lock is held for us, so we don't need any locking. */
46 static void flush_ldt(void *__mm)
48 struct mm_struct *mm = __mm;
51 if (this_cpu_read(cpu_tlbstate.loaded_mm) != mm)
55 set_ldt(pc->ldt->entries, pc->ldt->nr_entries);
57 refresh_ldt_segments();
60 /* The caller must call finalize_ldt_struct on the result. LDT starts zeroed. */
61 static struct ldt_struct *alloc_ldt_struct(unsigned int num_entries)
63 struct ldt_struct *new_ldt;
64 unsigned int alloc_size;
66 if (num_entries > LDT_ENTRIES)
69 new_ldt = kmalloc(sizeof(struct ldt_struct), GFP_KERNEL);
73 BUILD_BUG_ON(LDT_ENTRY_SIZE != sizeof(struct desc_struct));
74 alloc_size = num_entries * LDT_ENTRY_SIZE;
77 * Xen is very picky: it requires a page-aligned LDT that has no
78 * trailing nonzero bytes in any page that contains LDT descriptors.
79 * Keep it simple: zero the whole allocation and never allocate less
82 if (alloc_size > PAGE_SIZE)
83 new_ldt->entries = vzalloc(alloc_size);
85 new_ldt->entries = (void *)get_zeroed_page(GFP_KERNEL);
87 if (!new_ldt->entries) {
92 new_ldt->nr_entries = num_entries;
96 /* After calling this, the LDT is immutable. */
97 static void finalize_ldt_struct(struct ldt_struct *ldt)
99 paravirt_alloc_ldt(ldt->entries, ldt->nr_entries);
102 /* context.lock is held */
103 static void install_ldt(struct mm_struct *current_mm,
104 struct ldt_struct *ldt)
106 /* Synchronizes with READ_ONCE in load_mm_ldt. */
107 smp_store_release(¤t_mm->context.ldt, ldt);
109 /* Activate the LDT for all CPUs using current_mm. */
110 on_each_cpu_mask(mm_cpumask(current_mm), flush_ldt, current_mm, true);
113 static void free_ldt_struct(struct ldt_struct *ldt)
118 paravirt_free_ldt(ldt->entries, ldt->nr_entries);
119 if (ldt->nr_entries * LDT_ENTRY_SIZE > PAGE_SIZE)
120 vfree_atomic(ldt->entries);
122 free_page((unsigned long)ldt->entries);
127 * we do not have to muck with descriptors here, that is
128 * done in switch_mm() as needed.
130 int init_new_context_ldt(struct task_struct *tsk, struct mm_struct *mm)
132 struct ldt_struct *new_ldt;
133 struct mm_struct *old_mm;
136 mutex_init(&mm->context.lock);
137 old_mm = current->mm;
139 mm->context.ldt = NULL;
143 mutex_lock(&old_mm->context.lock);
144 if (!old_mm->context.ldt) {
145 mm->context.ldt = NULL;
149 new_ldt = alloc_ldt_struct(old_mm->context.ldt->nr_entries);
155 memcpy(new_ldt->entries, old_mm->context.ldt->entries,
156 new_ldt->nr_entries * LDT_ENTRY_SIZE);
157 finalize_ldt_struct(new_ldt);
159 mm->context.ldt = new_ldt;
162 mutex_unlock(&old_mm->context.lock);
167 * No need to lock the MM as we are the last user
169 * 64bit: Don't touch the LDT register - we're already in the next thread.
171 void destroy_context_ldt(struct mm_struct *mm)
173 free_ldt_struct(mm->context.ldt);
174 mm->context.ldt = NULL;
177 static int read_ldt(void __user *ptr, unsigned long bytecount)
179 struct mm_struct *mm = current->mm;
180 unsigned long entries_size;
183 mutex_lock(&mm->context.lock);
185 if (!mm->context.ldt) {
190 if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
191 bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
193 entries_size = mm->context.ldt->nr_entries * LDT_ENTRY_SIZE;
194 if (entries_size > bytecount)
195 entries_size = bytecount;
197 if (copy_to_user(ptr, mm->context.ldt->entries, entries_size)) {
202 if (entries_size != bytecount) {
203 /* Zero-fill the rest and pretend we read bytecount bytes. */
204 if (clear_user(ptr + entries_size, bytecount - entries_size)) {
212 mutex_unlock(&mm->context.lock);
216 static int read_default_ldt(void __user *ptr, unsigned long bytecount)
218 /* CHECKME: Can we use _one_ random number ? */
220 unsigned long size = 5 * sizeof(struct desc_struct);
222 unsigned long size = 128;
224 if (bytecount > size)
226 if (clear_user(ptr, bytecount))
231 static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
233 struct mm_struct *mm = current->mm;
234 struct ldt_struct *new_ldt, *old_ldt;
235 unsigned int old_nr_entries, new_nr_entries;
236 struct user_desc ldt_info;
237 struct desc_struct ldt;
241 if (bytecount != sizeof(ldt_info))
244 if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
248 if (ldt_info.entry_number >= LDT_ENTRIES)
250 if (ldt_info.contents == 3) {
253 if (ldt_info.seg_not_present == 0)
257 if ((oldmode && !ldt_info.base_addr && !ldt_info.limit) ||
258 LDT_empty(&ldt_info)) {
259 /* The user wants to clear the entry. */
260 memset(&ldt, 0, sizeof(ldt));
262 if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) {
267 fill_ldt(&ldt, &ldt_info);
272 mutex_lock(&mm->context.lock);
274 old_ldt = mm->context.ldt;
275 old_nr_entries = old_ldt ? old_ldt->nr_entries : 0;
276 new_nr_entries = max(ldt_info.entry_number + 1, old_nr_entries);
279 new_ldt = alloc_ldt_struct(new_nr_entries);
284 memcpy(new_ldt->entries, old_ldt->entries, old_nr_entries * LDT_ENTRY_SIZE);
286 new_ldt->entries[ldt_info.entry_number] = ldt;
287 finalize_ldt_struct(new_ldt);
289 install_ldt(mm, new_ldt);
290 free_ldt_struct(old_ldt);
294 mutex_unlock(&mm->context.lock);
299 SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr ,
300 unsigned long , bytecount)
306 ret = read_ldt(ptr, bytecount);
309 ret = write_ldt(ptr, bytecount, 1);
312 ret = read_default_ldt(ptr, bytecount);
315 ret = write_ldt(ptr, bytecount, 0);
319 * The SYSCALL_DEFINE() macros give us an 'unsigned long'
320 * return type, but tht ABI for sys_modify_ldt() expects
321 * 'int'. This cast gives us an int-sized value in %rax
322 * for the return code. The 'unsigned' is necessary so
323 * the compiler does not try to sign-extend the negative
324 * return codes into the high half of the register when
325 * taking the value from int->long.
327 return (unsigned int)ret;