1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
|
// SPDX-License-Identifier: GPL-2.0
/*
* shstk.c - Intel shadow stack support
*
* Copyright (c) 2021, Intel Corporation.
* Yu-cheng Yu <yu-cheng.yu@intel.com>
*/
#include <linux/sched.h>
#include <linux/bitops.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/sched/signal.h>
#include <linux/compat.h>
#include <linux/sizes.h>
#include <linux/user.h>
#include <asm/msr.h>
#include <asm/fpu/xstate.h>
#include <asm/fpu/types.h>
#include <asm/shstk.h>
#include <asm/special_insns.h>
#include <asm/fpu/api.h>
#include <asm/prctl.h>
static bool features_enabled(unsigned long features)
{
return current->thread.features & features;
}
static void features_set(unsigned long features)
{
current->thread.features |= features;
}
static void features_clr(unsigned long features)
{
current->thread.features &= ~features;
}
static unsigned long alloc_shstk(unsigned long size)
{
int flags = MAP_ANONYMOUS | MAP_PRIVATE | MAP_ABOVE4G;
struct mm_struct *mm = current->mm;
unsigned long addr, unused;
mmap_write_lock(mm);
addr = do_mmap(NULL, 0, size, PROT_READ, flags,
VM_SHADOW_STACK | VM_WRITE, 0, &unused, NULL);
mmap_write_unlock(mm);
return addr;
}
static unsigned long adjust_shstk_size(unsigned long size)
{
if (size)
return PAGE_ALIGN(size);
return PAGE_ALIGN(min_t(unsigned long long, rlimit(RLIMIT_STACK), SZ_4G));
}
static void unmap_shadow_stack(u64 base, u64 size)
{
while (1) {
int r;
r = vm_munmap(base, size);
/*
* vm_munmap() returns -EINTR when mmap_lock is held by
* something else, and that lock should not be held for a
* long time. Retry it for the case.
*/
if (r == -EINTR) {
cond_resched();
continue;
}
/*
* For all other types of vm_munmap() failure, either the
* system is out of memory or there is bug.
*/
WARN_ON_ONCE(r);
break;
}
}
static int shstk_setup(void)
{
struct thread_shstk *shstk = ¤t->thread.shstk;
unsigned long addr, size;
/* Already enabled */
if (features_enabled(ARCH_SHSTK_SHSTK))
return 0;
/* Also not supported for 32 bit and x32 */
if (!cpu_feature_enabled(X86_FEATURE_USER_SHSTK) || in_32bit_syscall())
return -EOPNOTSUPP;
size = adjust_shstk_size(0);
addr = alloc_shstk(size);
if (IS_ERR_VALUE(addr))
return PTR_ERR((void *)addr);
fpregs_lock_and_load();
wrmsrl(MSR_IA32_PL3_SSP, addr + size);
wrmsrl(MSR_IA32_U_CET, CET_SHSTK_EN);
fpregs_unlock();
shstk->base = addr;
shstk->size = size;
features_set(ARCH_SHSTK_SHSTK);
return 0;
}
void reset_thread_features(void)
{
memset(¤t->thread.shstk, 0, sizeof(struct thread_shstk));
current->thread.features = 0;
current->thread.features_locked = 0;
}
unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, unsigned long clone_flags,
unsigned long stack_size)
{
struct thread_shstk *shstk = &tsk->thread.shstk;
unsigned long addr, size;
/*
* If shadow stack is not enabled on the new thread, skip any
* switch to a new shadow stack.
*/
if (!features_enabled(ARCH_SHSTK_SHSTK))
return 0;
/*
* For CLONE_VM, except vfork, the child needs a separate shadow
* stack.
*/
if ((clone_flags & (CLONE_VFORK | CLONE_VM)) != CLONE_VM)
return 0;
size = adjust_shstk_size(stack_size);
addr = alloc_shstk(size);
if (IS_ERR_VALUE(addr))
return addr;
shstk->base = addr;
shstk->size = size;
return addr + size;
}
void shstk_free(struct task_struct *tsk)
{
struct thread_shstk *shstk = &tsk->thread.shstk;
if (!cpu_feature_enabled(X86_FEATURE_USER_SHSTK) ||
!features_enabled(ARCH_SHSTK_SHSTK))
return;
/*
* When fork() with CLONE_VM fails, the child (tsk) already has a
* shadow stack allocated, and exit_thread() calls this function to
* free it. In this case the parent (current) and the child share
* the same mm struct.
*/
if (!tsk->mm || tsk->mm != current->mm)
return;
unmap_shadow_stack(shstk->base, shstk->size);
}
static int shstk_disable(void)
{
if (!cpu_feature_enabled(X86_FEATURE_USER_SHSTK))
return -EOPNOTSUPP;
/* Already disabled? */
if (!features_enabled(ARCH_SHSTK_SHSTK))
return 0;
fpregs_lock_and_load();
/* Disable WRSS too when disabling shadow stack */
wrmsrl(MSR_IA32_U_CET, 0);
wrmsrl(MSR_IA32_PL3_SSP, 0);
fpregs_unlock();
shstk_free(current);
features_clr(ARCH_SHSTK_SHSTK);
return 0;
}
long shstk_prctl(struct task_struct *task, int option, unsigned long features)
{
if (option == ARCH_SHSTK_LOCK) {
task->thread.features_locked |= features;
return 0;
}
/* Don't allow via ptrace */
if (task != current)
return -EINVAL;
/* Do not allow to change locked features */
if (features & task->thread.features_locked)
return -EPERM;
/* Only support enabling/disabling one feature at a time. */
if (hweight_long(features) > 1)
return -EINVAL;
if (option == ARCH_SHSTK_DISABLE) {
return -EINVAL;
}
/* Handle ARCH_SHSTK_ENABLE */
return -EINVAL;
}
|
