CRIU and GDB need to get the current shadow stack and WRSS enablement
status. This information is already available via /proc/pid/status, but
this is inconvenient for CRIU because it involves parsing the text output
in an area of the code where this is difficult. Provide a status
arch_prctl(), ARCH_SHSTK_STATUS for retrieving the status. Have arg2 be a
userspace address, and make the new arch_prctl simply copy the features
out to userspace.
Suggested-by: Mike Rapoport <rppt@kernel.org>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Kees Cook <keescook@chromium.org>
---
v5:
- Fix typo in commit log
v4:
- New patch
---
Documentation/x86/shstk.rst | 6 ++++++
arch/x86/include/asm/shstk.h | 2 +-
arch/x86/include/uapi/asm/prctl.h | 1 +
arch/x86/kernel/process_64.c | 1 +
arch/x86/kernel/shstk.c | 8 +++++++-
5 files changed, 16 insertions(+), 2 deletions(-)
@@ -79,6 +79,11 @@ 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.
+arch_prctl(ARCH_SHSTK_STATUS, unsigned long addr)
+ Copy the currently enabled features to the address passed in addr. The
+ features are described using the bits passed into the others in
+ 'features'.
+
The return values are as follows. On success, return 0. On error, errno can
be::
@@ -86,6 +91,7 @@ be::
-ENOTSUPP if the feature is not supported by the hardware or
kernel.
-EINVAL arguments (non existing feature, etc)
+ -EFAULT if could not copy information back to userspace
The feature's bits supported are::
@@ -14,7 +14,7 @@ struct thread_shstk {
u64 size;
};
-long shstk_prctl(struct task_struct *task, int option, unsigned long features);
+long shstk_prctl(struct task_struct *task, int option, unsigned long arg2);
void reset_thread_features(void);
unsigned long shstk_alloc_thread_stack(struct task_struct *p, unsigned long clone_flags,
unsigned long stack_size);
@@ -26,6 +26,7 @@
#define ARCH_SHSTK_DISABLE 0x5002
#define ARCH_SHSTK_LOCK 0x5003
#define ARCH_SHSTK_UNLOCK 0x5004
+#define ARCH_SHSTK_STATUS 0x5005
/* ARCH_SHSTK_ features bits */
#define ARCH_SHSTK_SHSTK (1ULL << 0)
@@ -836,6 +836,7 @@ long do_arch_prctl_64(struct task_struct *task, int option, unsigned long arg2)
case ARCH_SHSTK_DISABLE:
case ARCH_SHSTK_LOCK:
case ARCH_SHSTK_UNLOCK:
+ case ARCH_SHSTK_STATUS:
return shstk_prctl(task, option, arg2);
default:
ret = -EINVAL;
@@ -452,8 +452,14 @@ SYSCALL_DEFINE3(map_shadow_stack, unsigned long, addr, unsigned long, size, unsi
return alloc_shstk(addr, aligned_size, size, set_tok);
}
-long shstk_prctl(struct task_struct *task, int option, unsigned long features)
+long shstk_prctl(struct task_struct *task, int option, unsigned long arg2)
{
+ unsigned long features = arg2;
+
+ if (option == ARCH_SHSTK_STATUS) {
+ return put_user(task->thread.features, (unsigned long __user *)arg2);
+ }
+
if (option == ARCH_SHSTK_LOCK) {
task->thread.features_locked |= features;
return 0;