[v4,38/39] x86/shstk: Add ARCH_SHSTK_UNLOCK
Commit Message
From: Mike Rapoport <rppt@linux.ibm.com>
Userspace loaders may lock features before a CRIU restore operation has
the chance to set them to whatever state is required by the process
being restored. Allow a way for CRIU to unlock features. Add it as an
arch_prctl() like the other shadow stack operations, but restrict it being
called by the ptrace arch_pctl() interface.
Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Tested-by: John Allen <john.allen@amd.com>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
[Merged into recent API changes, added commit log and docs]
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
v4:
- Add to docs that it is ptrace only.
- Remove "CET" references
v3:
- Depend on CONFIG_CHECKPOINT_RESTORE (Kees)
Documentation/x86/shstk.rst | 4 ++++
arch/x86/include/uapi/asm/prctl.h | 1 +
arch/x86/kernel/process_64.c | 1 +
arch/x86/kernel/shstk.c | 9 +++++++--
4 files changed, 13 insertions(+), 2 deletions(-)
Comments
On Fri, Dec 02, 2022 at 04:36:05PM -0800, Rick Edgecombe wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
>
> Userspace loaders may lock features before a CRIU restore operation has
> the chance to set them to whatever state is required by the process
> being restored. Allow a way for CRIU to unlock features. Add it as an
> arch_prctl() like the other shadow stack operations, but restrict it being
> called by the ptrace arch_pctl() interface.
>
> Tested-by: Pengfei Xu <pengfei.xu@intel.com>
> Tested-by: John Allen <john.allen@amd.com>
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
@@ -73,6 +73,10 @@ arch_prctl(ARCH_SHSTK_LOCK, unsigned long features)
are ignored. The mask is ORed with the existing value. So any feature bits
set here cannot be enabled or disabled afterwards.
+arch_prctl(ARCH_SHSTK_UNLOCK, unsigned long features)
+ Unlock features. 'features' is a mask of all features to unlock. All
+ bits set are processed, unset bits are ignored. Only works via ptrace.
+
The return values are as following:
On success, return 0. On error, errno can be::
@@ -30,6 +30,7 @@
#define ARCH_SHSTK_ENABLE 0x5001
#define ARCH_SHSTK_DISABLE 0x5002
#define ARCH_SHSTK_LOCK 0x5003
+#define ARCH_SHSTK_UNLOCK 0x5004
/* ARCH_SHSTK_ features bits */
#define ARCH_SHSTK_SHSTK (1ULL << 0)
@@ -921,6 +921,7 @@ long do_arch_prctl_64(struct task_struct *task, int option, unsigned long arg2)
case ARCH_SHSTK_ENABLE:
case ARCH_SHSTK_DISABLE:
case ARCH_SHSTK_LOCK:
+ case ARCH_SHSTK_UNLOCK:
return shstk_prctl(task, option, arg2);
default:
ret = -EINVAL;
@@ -455,9 +455,14 @@ long shstk_prctl(struct task_struct *task, int option, unsigned long features)
return 0;
}
- /* Don't allow via ptrace */
- if (task != current)
+ /* Only allow via ptrace */
+ if (task != current) {
+ if (option == ARCH_SHSTK_UNLOCK && IS_ENABLED(CONFIG_CHECKPOINT_RESTORE)) {
+ task->thread.features_locked &= ~features;
+ return 0;
+ }
return -EINVAL;
+ }
/* Do not allow to change locked features */
if (features & task->thread.features_locked)