From:   Rick Edgecombe <rick.p.edgecombe@intel.com>
To:     x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-mm@kvack.org,
        linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
        Arnd Bergmann <arnd@arndb.de>,
        Andy Lutomirski <luto@kernel.org>,
        Balbir Singh <bsingharora@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
        Florian Weimer <fweimer@redhat.com>,
        "H . J . Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Kees Cook <keescook@chromium.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Weijiang Yang <weijiang.yang@intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        John Allen <john.allen@amd.com>, kcc@google.com,
        eranian@google.com, rppt@kernel.org, jamorris@linux.microsoft.com,
        dethoma@microsoft.com, akpm@linux-foundation.org,
        Andrew.Cooper3@citrix.com, christina.schimpe@intel.com,
        david@redhat.com, debug@rivosinc.com
Cc:     rick.p.edgecombe@intel.com
Subject: [PATCH v6 41/41] x86/shstk: Add ARCH_SHSTK_STATUS
Date:   Sat, 18 Feb 2023 13:14:33 -0800
Message-Id: <20230218211433.26859-42-rick.p.edgecombe@intel.com>
In-Reply-To: <20230218211433.26859-1-rick.p.edgecombe@intel.com>
References: <20230218211433.26859-1-rick.p.edgecombe@intel.com>
Precedence: bulk

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.

Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Suggested-by: Mike Rapoport <rppt@kernel.org>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>

---
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(-)

diff --git a/Documentation/x86/shstk.rst b/Documentation/x86/shstk.rst
index e8ed5fc0f7ae..7f4af798794e 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 follows. On success, return 0. On error, errno can
 be::
 
@@ -84,6 +89,7 @@ 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::
 
diff --git a/arch/x86/include/asm/shstk.h b/arch/x86/include/asm/shstk.h
index acee68d30a07..be9267897211 100644
--- a/arch/x86/include/asm/shstk.h
+++ b/arch/x86/include/asm/shstk.h
@@ -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);
 int shstk_alloc_thread_stack(struct task_struct *p, unsigned long clone_flags,
 			     unsigned long stack_size,
diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h
index 200efbbe5809..1b85bc876c2d 100644
--- a/arch/x86/include/uapi/asm/prctl.h
+++ b/arch/x86/include/uapi/asm/prctl.h
@@ -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)
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index d368854fa9c4..dde43caf196e 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -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;
diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
index 3197ff824809..4069d5bbbe8c 100644
--- a/arch/x86/kernel/shstk.c
+++ b/arch/x86/kernel/shstk.c
@@ -444,8 +444,14 @@ 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