[tip:,x86/shstk] x86/shstk: Add ARCH_SHSTK_UNLOCK
Commit Message
The following commit has been merged into the x86/shstk branch of tip:
Commit-ID: d30299329def886f8bcf068da204011a08ab75f9
Gitweb: https://git.kernel.org/tip/d30299329def886f8bcf068da204011a08ab75f9
Author: Mike Rapoport <rppt@linux.ibm.com>
AuthorDate: Sat, 18 Mar 2023 17:15:34 -07:00
Committer: Dave Hansen <dave.hansen@linux.intel.com>
CommitterDate: Mon, 20 Mar 2023 09:01:12 -07:00
x86/shstk: Add ARCH_SHSTK_UNLOCK
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.
[Merged into recent API changes, added commit log and docs]
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/all/20230319001535.23210-40-rick.p.edgecombe%40intel.com
---
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(-)
@@ -75,6 +75,10 @@ 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 follows. On success, return 0. On error, errno can
be::
@@ -25,6 +25,7 @@
#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)
@@ -835,6 +835,7 @@ 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;
@@ -459,9 +459,14 @@ 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)