Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
riscv: Implement arch-agnostic shadow stack prctls
Implement an architecture-agnostic prctl() interface for setting and
getting shadow stack status. The prctls implemented are
PR_GET_SHADOW_STACK_STATUS, PR_SET_SHADOW_STACK_STATUS and
PR_LOCK_SHADOW_STACK_STATUS.
As part of PR_SET_SHADOW_STACK_STATUS/PR_GET_SHADOW_STACK_STATUS, only
PR_SHADOW_STACK_ENABLE is implemented because RISCV allows each mode to
write to their own shadow stack using 'sspush' or 'ssamoswap'.
PR_LOCK_SHADOW_STACK_STATUS locks the current shadow stack enablement
configuration.
Reviewed-by: Zong Li <zong.li@sifive.com>
Signed-off-by: Deepak Gupta <debug@rivosinc.com>
Tested-by: Andreas Korb <andreas.korb@aisec.fraunhofer.de> # QEMU, custom CVA6
Tested-by: Valentin Haudiquet <valentin.haudiquet@canonical.com>
Link: https://patch.msgid.link/20251112-v5_user_cfi_series-v23-12-b55691eacf4f@rivosinc.com
[pjw@kernel.org: cleaned up patch description]
Signed-off-by: Paul Walmsley <pjw@kernel.org>
authored by
Deepak Gupta
and committed by
Paul Walmsley
61a02002
fd44a4a8
+134
+16
arch/riscv/include/asm/usercfi.h
+16
arch/riscv/include/asm/usercfi.h
···
7
7
8
8
#ifndef __ASSEMBLER__
9
9
#include <linux/types.h>
10
+
#include <linux/prctl.h>
10
11
11
12
struct task_struct;
12
13
struct kernel_clone_args;
···
15
14
#ifdef CONFIG_RISCV_USER_CFI
16
15
struct cfi_state {
17
16
unsigned long ubcfi_en : 1; /* Enable for backward cfi. */
17
+
unsigned long ubcfi_locked : 1;
18
18
unsigned long user_shdw_stk; /* Current user shadow stack pointer */
19
19
unsigned long shdw_stk_base; /* Base address of shadow stack */
20
20
unsigned long shdw_stk_size; /* size of shadow stack */
···
28
26
unsigned long get_shstk_base(struct task_struct *task, unsigned long *size);
29
27
void set_active_shstk(struct task_struct *task, unsigned long shstk_addr);
30
28
bool is_shstk_enabled(struct task_struct *task);
29
+
bool is_shstk_locked(struct task_struct *task);
30
+
bool is_shstk_allocated(struct task_struct *task);
31
+
void set_shstk_lock(struct task_struct *task);
32
+
void set_shstk_status(struct task_struct *task, bool enable);
33
+
34
+
#define PR_SHADOW_STACK_SUPPORTED_STATUS_MASK (PR_SHADOW_STACK_ENABLE)
31
35
32
36
#else
33
37
···
48
40
#define set_active_shstk(task, shstk_addr) do {} while (0)
49
41
50
42
#define is_shstk_enabled(task) false
43
+
44
+
#define is_shstk_locked(task) false
45
+
46
+
#define is_shstk_allocated(task) false
47
+
48
+
#define set_shstk_lock(task) do {} while (0)
49
+
50
+
#define set_shstk_status(task, enable) do {} while (0)
51
51
52
52
#endif /* CONFIG_RISCV_USER_CFI */
53
53
+8
arch/riscv/kernel/process.c
+8
arch/riscv/kernel/process.c
···
156
156
regs->epc = pc;
157
157
regs->sp = sp;
158
158
159
+
/*
160
+
* clear shadow stack state on exec.
161
+
* libc will set it later via prctl.
162
+
*/
163
+
set_shstk_status(current, false);
164
+
set_shstk_base(current, 0, 0);
165
+
set_active_shstk(current, 0);
166
+
159
167
#ifdef CONFIG_64BIT
160
168
regs->status &= ~SR_UXL;
161
169
+110
arch/riscv/kernel/usercfi.c
+110
arch/riscv/kernel/usercfi.c
···
24
24
return task->thread_info.user_cfi_state.ubcfi_en;
25
25
}
26
26
27
+
bool is_shstk_allocated(struct task_struct *task)
28
+
{
29
+
return task->thread_info.user_cfi_state.shdw_stk_base;
30
+
}
31
+
32
+
bool is_shstk_locked(struct task_struct *task)
33
+
{
34
+
return task->thread_info.user_cfi_state.ubcfi_locked;
35
+
}
36
+
27
37
void set_shstk_base(struct task_struct *task, unsigned long shstk_addr, unsigned long size)
28
38
{
29
39
task->thread_info.user_cfi_state.shdw_stk_base = shstk_addr;
···
50
40
void set_active_shstk(struct task_struct *task, unsigned long shstk_addr)
51
41
{
52
42
task->thread_info.user_cfi_state.user_shdw_stk = shstk_addr;
43
+
}
44
+
45
+
void set_shstk_status(struct task_struct *task, bool enable)
46
+
{
47
+
if (!cpu_supports_shadow_stack())
48
+
return;
49
+
50
+
task->thread_info.user_cfi_state.ubcfi_en = enable ? 1 : 0;
51
+
52
+
if (enable)
53
+
task->thread.envcfg |= ENVCFG_SSE;
54
+
else
55
+
task->thread.envcfg &= ~ENVCFG_SSE;
56
+
57
+
csr_write(CSR_ENVCFG, task->thread.envcfg);
58
+
}
59
+
60
+
void set_shstk_lock(struct task_struct *task)
61
+
{
62
+
task->thread_info.user_cfi_state.ubcfi_locked = 1;
53
63
}
54
64
55
65
/*
···
287
257
288
258
vm_munmap(base, size);
289
259
set_shstk_base(tsk, 0, 0);
260
+
}
261
+
262
+
int arch_get_shadow_stack_status(struct task_struct *t, unsigned long __user *status)
263
+
{
264
+
unsigned long bcfi_status = 0;
265
+
266
+
if (!cpu_supports_shadow_stack())
267
+
return -EINVAL;
268
+
269
+
/* this means shadow stack is enabled on the task */
270
+
bcfi_status |= (is_shstk_enabled(t) ? PR_SHADOW_STACK_ENABLE : 0);
271
+
272
+
return copy_to_user(status, &bcfi_status, sizeof(bcfi_status)) ? -EFAULT : 0;
273
+
}
274
+
275
+
int arch_set_shadow_stack_status(struct task_struct *t, unsigned long status)
276
+
{
277
+
unsigned long size = 0, addr = 0;
278
+
bool enable_shstk = false;
279
+
280
+
if (!cpu_supports_shadow_stack())
281
+
return -EINVAL;
282
+
283
+
/* Reject unknown flags */
284
+
if (status & ~PR_SHADOW_STACK_SUPPORTED_STATUS_MASK)
285
+
return -EINVAL;
286
+
287
+
/* bcfi status is locked and further can't be modified by user */
288
+
if (is_shstk_locked(t))
289
+
return -EINVAL;
290
+
291
+
enable_shstk = status & PR_SHADOW_STACK_ENABLE;
292
+
/* Request is to enable shadow stack and shadow stack is not enabled already */
293
+
if (enable_shstk && !is_shstk_enabled(t)) {
294
+
/* shadow stack was allocated and enable request again
295
+
* no need to support such usecase and return EINVAL.
296
+
*/
297
+
if (is_shstk_allocated(t))
298
+
return -EINVAL;
299
+
300
+
size = calc_shstk_size(0);
301
+
addr = allocate_shadow_stack(0, size, 0, false);
302
+
if (IS_ERR_VALUE(addr))
303
+
return -ENOMEM;
304
+
set_shstk_base(t, addr, size);
305
+
set_active_shstk(t, addr + size);
306
+
}
307
+
308
+
/*
309
+
* If a request to disable shadow stack happens, let's go ahead and release it
310
+
* Although, if CLONE_VFORKed child did this, then in that case we will end up
311
+
* not releasing the shadow stack (because it might be needed in parent). Although
312
+
* we will disable it for VFORKed child. And if VFORKed child tries to enable again
313
+
* then in that case, it'll get entirely new shadow stack because following condition
314
+
* are true
315
+
* - shadow stack was not enabled for vforked child
316
+
* - shadow stack base was anyways pointing to 0
317
+
* This shouldn't be a big issue because we want parent to have availability of shadow
318
+
* stack whenever VFORKed child releases resources via exit or exec but at the same
319
+
* time we want VFORKed child to break away and establish new shadow stack if it desires
320
+
*
321
+
*/
322
+
if (!enable_shstk)
323
+
shstk_release(t);
324
+
325
+
set_shstk_status(t, enable_shstk);
326
+
return 0;
327
+
}
328
+
329
+
int arch_lock_shadow_stack_status(struct task_struct *task,
330
+
unsigned long arg)
331
+
{
332
+
/* If shtstk not supported or not enabled on task, nothing to lock here */
333
+
if (!cpu_supports_shadow_stack() ||
334
+
!is_shstk_enabled(task) || arg != 0)
335
+
return -EINVAL;
336
+
337
+
set_shstk_lock(task);
338
+
339
+
return 0;
290
340
}