1 files changed, 272 insertions, 0 deletions
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
new file mode 100644
index 000000000..c37886d75
--- /dev/null
+++ b/arch/x86/kernel/ldt.c
@@ -0,0 +1,272 @@
+/*
+ * Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
+ * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
+ * Copyright (C) 2002 Andi Kleen
+ *
+ * This handles calls from both 32bit and 64bit mode.
+ */
+
+#include <linux/errno.h>
+#include <linux/gfp.h>
+#include <linux/sched.h>
+#include <linux/string.h>
+#include <linux/mm.h>
+#include <linux/smp.h>
+#include <linux/vmalloc.h>
+#include <linux/uaccess.h>
+
+#include <asm/ldt.h>
+#include <asm/desc.h>
+#include <asm/mmu_context.h>
+#include <asm/syscalls.h>
+
+#ifdef CONFIG_SMP
+static void flush_ldt(void *current_mm)
+{
+	if (current->active_mm == current_mm)
+		load_LDT(&current->active_mm->context);
+}
+#endif
+
+static int alloc_ldt(mm_context_t *pc, int mincount, int reload)
+{
+	void *oldldt, *newldt;
+	int oldsize;
+
+	if (mincount <= pc->size)
+		return 0;
+	oldsize = pc->size;
+	mincount = (mincount + (PAGE_SIZE / LDT_ENTRY_SIZE - 1)) &
+			(~(PAGE_SIZE / LDT_ENTRY_SIZE - 1));
+	if (mincount * LDT_ENTRY_SIZE > PAGE_SIZE)
+		newldt = vmalloc(mincount * LDT_ENTRY_SIZE);
+	else
+		newldt = (void *)__get_free_page(GFP_KERNEL);
+
+	if (!newldt)
+		return -ENOMEM;
+
+	if (oldsize)
+		memcpy(newldt, pc->ldt, oldsize * LDT_ENTRY_SIZE);
+	oldldt = pc->ldt;
+	memset(newldt + oldsize * LDT_ENTRY_SIZE, 0,
+	       (mincount - oldsize) * LDT_ENTRY_SIZE);
+
+	paravirt_alloc_ldt(newldt, mincount);
+
+#ifdef CONFIG_X86_64
+	/* CHECKME: Do we really need this ? */
+	wmb();
+#endif
+	pc->ldt = newldt;
+	wmb();
+	pc->size = mincount;
+	wmb();
+
+	if (reload) {
+#ifdef CONFIG_SMP
+		preempt_disable();
+		load_LDT(pc);
+		if (!cpumask_equal(mm_cpumask(current->mm),
+				   cpumask_of(smp_processor_id())))
+			smp_call_function(flush_ldt, current->mm, 1);
+		preempt_enable();
+#else
+		load_LDT(pc);
+#endif
+	}
+	if (oldsize) {
+		paravirt_free_ldt(oldldt, oldsize);
+		if (oldsize * LDT_ENTRY_SIZE > PAGE_SIZE)
+			vfree(oldldt);
+		else
+			put_page(virt_to_page(oldldt));
+	}
+	return 0;
+}
+
+static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
+{
+	int err = alloc_ldt(new, old->size, 0);
+	int i;
+
+	if (err < 0)
+		return err;
+
+	for (i = 0; i < old->size; i++)
+		write_ldt_entry(new->ldt, i, old->ldt + i * LDT_ENTRY_SIZE);
+	return 0;
+}
+
+/*
+ * we do not have to muck with descriptors here, that is
+ * done in switch_mm() as needed.
+ */
+int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
+{
+	struct mm_struct *old_mm;
+	int retval = 0;
+
+	mutex_init(&mm->context.lock);
+	mm->context.size = 0;
+	old_mm = current->mm;
+	if (old_mm && old_mm->context.size > 0) {
+		mutex_lock(&old_mm->context.lock);
+		retval = copy_ldt(&mm->context, &old_mm->context);
+		mutex_unlock(&old_mm->context.lock);
+	}
+	return retval;
+}
+
+/*
+ * No need to lock the MM as we are the last user
+ *
+ * 64bit: Don't touch the LDT register - we're already in the next thread.
+ */
+void destroy_context(struct mm_struct *mm)
+{
+	if (mm->context.size) {
+#ifdef CONFIG_X86_32
+		/* CHECKME: Can this ever happen ? */
+		if (mm == current->active_mm)
+			clear_LDT();
+#endif
+		paravirt_free_ldt(mm->context.ldt, mm->context.size);
+		if (mm->context.size * LDT_ENTRY_SIZE > PAGE_SIZE)
+			vfree(mm->context.ldt);
+		else
+			put_page(virt_to_page(mm->context.ldt));
+		mm->context.size = 0;
+	}
+}
+
+static int read_ldt(void __user *ptr, unsigned long bytecount)
+{
+	int err;
+	unsigned long size;
+	struct mm_struct *mm = current->mm;
+
+	if (!mm->context.size)
+		return 0;
+	if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
+		bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
+
+	mutex_lock(&mm->context.lock);
+	size = mm->context.size * LDT_ENTRY_SIZE;
+	if (size > bytecount)
+		size = bytecount;
+
+	err = 0;
+	if (copy_to_user(ptr, mm->context.ldt, size))
+		err = -EFAULT;
+	mutex_unlock(&mm->context.lock);
+	if (err < 0)
+		goto error_return;
+	if (size != bytecount) {
+		/* zero-fill the rest */
+		if (clear_user(ptr + size, bytecount - size) != 0) {
+			err = -EFAULT;
+			goto error_return;
+		}
+	}
+	return bytecount;
+error_return:
+	return err;
+}
+
+static int read_default_ldt(void __user *ptr, unsigned long bytecount)
+{
+	/* CHECKME: Can we use _one_ random number ? */
+#ifdef CONFIG_X86_32
+	unsigned long size = 5 * sizeof(struct desc_struct);
+#else
+	unsigned long size = 128;
+#endif
+	if (bytecount > size)
+		bytecount = size;
+	if (clear_user(ptr, bytecount))
+		return -EFAULT;
+	return bytecount;
+}
+
+static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
+{
+	struct mm_struct *mm = current->mm;
+	struct desc_struct ldt;
+	int error;
+	struct user_desc ldt_info;
+
+	error = -EINVAL;
+	if (bytecount != sizeof(ldt_info))
+		goto out;
+	error = -EFAULT;
+	if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
+		goto out;
+
+	error = -EINVAL;
+	if (ldt_info.entry_number >= LDT_ENTRIES)
+		goto out;
+	if (ldt_info.contents == 3) {
+		if (oldmode)
+			goto out;
+		if (ldt_info.seg_not_present == 0)
+			goto out;
+	}
+
+	mutex_lock(&mm->context.lock);
+	if (ldt_info.entry_number >= mm->context.size) {
+		error = alloc_ldt(&current->mm->context,
+				  ldt_info.entry_number + 1, 1);
+		if (error < 0)
+			goto out_unlock;
+	}
+
+	/* Allow LDTs to be cleared by the user. */
+	if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
+		if (oldmode || LDT_empty(&ldt_info)) {
+			memset(&ldt, 0, sizeof(ldt));
+			goto install;
+		}
+	}
+
+	if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) {
+		error = -EINVAL;
+		goto out_unlock;
+	}
+
+	fill_ldt(&ldt, &ldt_info);
+	if (oldmode)
+		ldt.avl = 0;
+
+	/* Install the new entry ...  */
+install:
+	write_ldt_entry(mm->context.ldt, ldt_info.entry_number, &ldt);
+	error = 0;
+
+out_unlock:
+	mutex_unlock(&mm->context.lock);
+out:
+	return error;
+}
+
+asmlinkage int sys_modify_ldt(int func, void __user *ptr,
+			      unsigned long bytecount)
+{
+	int ret = -ENOSYS;
+
+	switch (func) {
+	case 0:
+		ret = read_ldt(ptr, bytecount);
+		break;
+	case 1:
+		ret = write_ldt(ptr, bytecount, 1);
+		break;
+	case 2:
+		ret = read_default_ldt(ptr, bytecount);
+		break;
+	case 0x11:
+		ret = write_ldt(ptr, bytecount, 0);
+		break;
+	}
+	return ret;
+}