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- #include <linux/kernel.h>
- #include <linux/errno.h>
- #include <linux/sched.h>
- #include <linux/user.h>
- #include <linux/regset.h>
- #include <linux/syscalls.h>
- #include <asm/uaccess.h>
- #include <asm/desc.h>
- #include <asm/ldt.h>
- #include <asm/processor.h>
- #include <asm/proto.h>
- #include "tls.h"
- /*
- * sys_alloc_thread_area: get a yet unused TLS descriptor index.
- */
- static int get_free_idx(void)
- {
- struct thread_struct *t = ¤t->thread;
- int idx;
- for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
- if (desc_empty(&t->tls_array[idx]))
- return idx + GDT_ENTRY_TLS_MIN;
- return -ESRCH;
- }
- static bool tls_desc_okay(const struct user_desc *info)
- {
- /*
- * For historical reasons (i.e. no one ever documented how any
- * of the segmentation APIs work), user programs can and do
- * assume that a struct user_desc that's all zeros except for
- * entry_number means "no segment at all". This never actually
- * worked. In fact, up to Linux 3.19, a struct user_desc like
- * this would create a 16-bit read-write segment with base and
- * limit both equal to zero.
- *
- * That was close enough to "no segment at all" until we
- * hardened this function to disallow 16-bit TLS segments. Fix
- * it up by interpreting these zeroed segments the way that they
- * were almost certainly intended to be interpreted.
- *
- * The correct way to ask for "no segment at all" is to specify
- * a user_desc that satisfies LDT_empty. To keep everything
- * working, we accept both.
- *
- * Note that there's a similar kludge in modify_ldt -- look at
- * the distinction between modes 1 and 0x11.
- */
- if (LDT_empty(info) || LDT_zero(info))
- return true;
- /*
- * espfix is required for 16-bit data segments, but espfix
- * only works for LDT segments.
- */
- if (!info->seg_32bit)
- return false;
- /* Only allow data segments in the TLS array. */
- if (info->contents > 1)
- return false;
- /*
- * Non-present segments with DPL 3 present an interesting attack
- * surface. The kernel should handle such segments correctly,
- * but TLS is very difficult to protect in a sandbox, so prevent
- * such segments from being created.
- *
- * If userspace needs to remove a TLS entry, it can still delete
- * it outright.
- */
- if (info->seg_not_present)
- return false;
- return true;
- }
- static void set_tls_desc(struct task_struct *p, int idx,
- const struct user_desc *info, int n)
- {
- struct thread_struct *t = &p->thread;
- struct desc_struct *desc = &t->tls_array[idx - GDT_ENTRY_TLS_MIN];
- int cpu;
- /*
- * We must not get preempted while modifying the TLS.
- */
- cpu = get_cpu();
- while (n-- > 0) {
- if (LDT_empty(info) || LDT_zero(info))
- desc->a = desc->b = 0;
- else
- fill_ldt(desc, info);
- ++info;
- ++desc;
- }
- if (t == ¤t->thread)
- load_TLS(t, cpu);
- put_cpu();
- }
- /*
- * Set a given TLS descriptor:
- */
- int do_set_thread_area(struct task_struct *p, int idx,
- struct user_desc __user *u_info,
- int can_allocate)
- {
- struct user_desc info;
- if (copy_from_user(&info, u_info, sizeof(info)))
- return -EFAULT;
- if (!tls_desc_okay(&info))
- return -EINVAL;
- if (idx == -1)
- idx = info.entry_number;
- /*
- * index -1 means the kernel should try to find and
- * allocate an empty descriptor:
- */
- if (idx == -1 && can_allocate) {
- idx = get_free_idx();
- if (idx < 0)
- return idx;
- if (put_user(idx, &u_info->entry_number))
- return -EFAULT;
- }
- if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
- return -EINVAL;
- set_tls_desc(p, idx, &info, 1);
- return 0;
- }
- SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, u_info)
- {
- return do_set_thread_area(current, -1, u_info, 1);
- }
- /*
- * Get the current Thread-Local Storage area:
- */
- static void fill_user_desc(struct user_desc *info, int idx,
- const struct desc_struct *desc)
- {
- memset(info, 0, sizeof(*info));
- info->entry_number = idx;
- info->base_addr = get_desc_base(desc);
- info->limit = get_desc_limit(desc);
- info->seg_32bit = desc->d;
- info->contents = desc->type >> 2;
- info->read_exec_only = !(desc->type & 2);
- info->limit_in_pages = desc->g;
- info->seg_not_present = !desc->p;
- info->useable = desc->avl;
- #ifdef CONFIG_X86_64
- info->lm = desc->l;
- #endif
- }
- int do_get_thread_area(struct task_struct *p, int idx,
- struct user_desc __user *u_info)
- {
- struct user_desc info;
- if (idx == -1 && get_user(idx, &u_info->entry_number))
- return -EFAULT;
- if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
- return -EINVAL;
- fill_user_desc(&info, idx,
- &p->thread.tls_array[idx - GDT_ENTRY_TLS_MIN]);
- if (copy_to_user(u_info, &info, sizeof(info)))
- return -EFAULT;
- return 0;
- }
- SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, u_info)
- {
- return do_get_thread_area(current, -1, u_info);
- }
- int regset_tls_active(struct task_struct *target,
- const struct user_regset *regset)
- {
- struct thread_struct *t = &target->thread;
- int n = GDT_ENTRY_TLS_ENTRIES;
- while (n > 0 && desc_empty(&t->tls_array[n - 1]))
- --n;
- return n;
- }
- int regset_tls_get(struct task_struct *target, const struct user_regset *regset,
- unsigned int pos, unsigned int count,
- void *kbuf, void __user *ubuf)
- {
- const struct desc_struct *tls;
- if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
- (pos % sizeof(struct user_desc)) != 0 ||
- (count % sizeof(struct user_desc)) != 0)
- return -EINVAL;
- pos /= sizeof(struct user_desc);
- count /= sizeof(struct user_desc);
- tls = &target->thread.tls_array[pos];
- if (kbuf) {
- struct user_desc *info = kbuf;
- while (count-- > 0)
- fill_user_desc(info++, GDT_ENTRY_TLS_MIN + pos++,
- tls++);
- } else {
- struct user_desc __user *u_info = ubuf;
- while (count-- > 0) {
- struct user_desc info;
- fill_user_desc(&info, GDT_ENTRY_TLS_MIN + pos++, tls++);
- if (__copy_to_user(u_info++, &info, sizeof(info)))
- return -EFAULT;
- }
- }
- return 0;
- }
- int regset_tls_set(struct task_struct *target, const struct user_regset *regset,
- unsigned int pos, unsigned int count,
- const void *kbuf, const void __user *ubuf)
- {
- struct user_desc infobuf[GDT_ENTRY_TLS_ENTRIES];
- const struct user_desc *info;
- int i;
- if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
- (pos % sizeof(struct user_desc)) != 0 ||
- (count % sizeof(struct user_desc)) != 0)
- return -EINVAL;
- if (kbuf)
- info = kbuf;
- else if (__copy_from_user(infobuf, ubuf, count))
- return -EFAULT;
- else
- info = infobuf;
- for (i = 0; i < count / sizeof(struct user_desc); i++)
- if (!tls_desc_okay(info + i))
- return -EINVAL;
- set_tls_desc(target,
- GDT_ENTRY_TLS_MIN + (pos / sizeof(struct user_desc)),
- info, count / sizeof(struct user_desc));
- return 0;
- }
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