Contributors: 12
| Author |
Tokens |
Token Proportion |
Commits |
Commit Proportion |
| Roland McGrath |
450 |
37.34% |
4 |
16.00% |
| Andi Kleen |
394 |
32.70% |
5 |
20.00% |
| Andrew Lutomirski |
264 |
21.91% |
5 |
20.00% |
| Al Viro |
52 |
4.32% |
3 |
12.00% |
| Dianzhang Chen |
26 |
2.16% |
1 |
4.00% |
| Thomas Gleixner |
10 |
0.83% |
1 |
4.00% |
| H. Peter Anvin |
3 |
0.25% |
1 |
4.00% |
| Jaswinder Singh Rajput |
2 |
0.17% |
1 |
4.00% |
| Greg Kroah-Hartman |
1 |
0.08% |
1 |
4.00% |
| Linus Torvalds |
1 |
0.08% |
1 |
4.00% |
| Glauber de Oliveira Costa |
1 |
0.08% |
1 |
4.00% |
| Dan Carpenter |
1 |
0.08% |
1 |
4.00% |
| Total |
1205 |
|
25 |
|
// SPDX-License-Identifier: GPL-2.0
#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 <linux/nospec.h>
#include <linux/uaccess.h>
#include <asm/desc.h>
#include <asm/ldt.h>
#include <asm/processor.h>
#include <asm/proto.h>
#include <asm/gsseg.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))
memset(desc, 0, sizeof(*desc));
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;
unsigned short __maybe_unused sel, modified_sel;
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);
/*
* If DS, ES, FS, or GS points to the modified segment, forcibly
* refresh it. Only needed on x86_64 because x86_32 reloads them
* on return to user mode.
*/
modified_sel = (idx << 3) | 3;
if (p == current) {
#ifdef CONFIG_X86_64
savesegment(ds, sel);
if (sel == modified_sel)
loadsegment(ds, sel);
savesegment(es, sel);
if (sel == modified_sel)
loadsegment(es, sel);
savesegment(fs, sel);
if (sel == modified_sel)
loadsegment(fs, sel);
#endif
savesegment(gs, sel);
if (sel == modified_sel)
load_gs_index(sel);
} else {
#ifdef CONFIG_X86_64
if (p->thread.fsindex == modified_sel)
p->thread.fsbase = info.base_addr;
if (p->thread.gsindex == modified_sel)
p->thread.gsbase = info.base_addr;
#endif
}
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;
int index;
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;
index = idx - GDT_ENTRY_TLS_MIN;
index = array_index_nospec(index,
GDT_ENTRY_TLS_MAX - GDT_ENTRY_TLS_MIN + 1);
fill_user_desc(&info, idx, &p->thread.tls_array[index]);
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,
struct membuf to)
{
const struct desc_struct *tls;
struct user_desc v;
int pos;
for (pos = 0, tls = target->thread.tls_array; to.left; pos++, tls++) {
fill_user_desc(&v, GDT_ENTRY_TLS_MIN + pos, tls);
membuf_write(&to, &v, sizeof(v));
}
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;
}