[PATCH v4 39/39] x86/shstk: Add ARCH_SHSTK_STATUS

Rick Edgecombe
2022-12-03T00:44:00Z

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 incovienent 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.

Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Requested-by: Mike Rapoport <rppt@kernel.org>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---

v4:
- New patch

Documentation/x86/shstk.rst | 6 ++++++
arch/x86/include/asm/shstk.h | 4 ++--
arch/x86/include/uapi/asm/prctl.h | 1 +
arch/x86/kernel/process_64.c | 1 +
arch/x86/kernel/shstk.c | 8 +++++++-
5 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/Documentation/x86/shstk.rst b/Documentation/x86/shstk.rst
index 0d7d1ccfff06..b3eb87046c27 100644
--- a/Documentation/x86/shstk.rst
+++ b/Documentation/x86/shstk.rst
@@ -77,6 +77,11 @@ 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 following:
On success, return 0. On error, errno can be::

@@ -84,6 +89,7 @@ The return values are as following:
-EOPNOTSUPP if the feature is not supported by the hardware or
disabled by kernel parameter.
-EINVAL arguments (non existing feature, etc)
+ -EFAULT if could not copy information back to userspace

The feature's bits supported are::

diff --git a/arch/x86/include/asm/shstk.h b/arch/x86/include/asm/shstk.h
index c82f22fd5e6d..23bfb63c597d 100644
--- a/arch/x86/include/asm/shstk.h
+++ b/arch/x86/include/asm/shstk.h
@@ -15,7 +15,7 @@ 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);
int shstk_alloc_thread_stack(struct task_struct *p, unsigned long clone_flags,
unsigned long stack_size,
@@ -31,7 +31,7 @@ static inline bool shstk_enabled(void)
}
#else
static inline long shstk_prctl(struct task_struct *task, int option,
- unsigned long features) { return -EINVAL; }
+ unsigned long arg2) { return -EINVAL; }
static inline void reset_thread_features(void) {}
static inline int shstk_alloc_thread_stack(struct task_struct *p,
unsigned long clone_flags,
diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h
index 0c95688cf58e..abe3fe6db6d2 100644
--- a/arch/x86/include/uapi/asm/prctl.h
+++ b/arch/x86/include/uapi/asm/prctl.h
@@ -31,6 +31,7 @@
#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)
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 2be6e01fb144..5dcf5426241b 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -922,6 +922,7 @@ 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;
diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
index 95579f7bace3..05f8dcc19dbc 100644
--- a/arch/x86/kernel/shstk.c
+++ b/arch/x86/kernel/shstk.c
@@ -448,8 +448,14 @@ 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;
--
2.17.1