[PATCH 01/35] prctl: arch-agnostic prctl for shadow stack

[Mark Brown]

From: Deepak Gupta <debug at rivosinc.com>

Three architectures (x86, aarch64, riscv) have announced support for
shadow stack.  This patch adds arch-agnostic prtcl support to enable
/disable/get/set status of shadow stack and forward control (landing pad)
flow cfi statuses.

New prctls are
      - PR_GET_SHADOW_STACK_STATUS, PR_SET_SHADOW_STACK_STATUS

Signed-off-by: Deepak Gupta <debug at rivosinc.com>
[Rebased onto current kernels, renumbering to track other allocations
 already upstream, dropping indirect LP, updating to pass arg to set
  by value, fix missing prototypes for weak functions and update title.
  -- broonie]
Signed-off-by: Mark Brown <broonie at kernel.org>
---
 include/linux/mm.h         |  3 +++
 include/uapi/linux/prctl.h | 17 +++++++++++++++++
 kernel/sys.c               | 20 ++++++++++++++++++++
 3 files changed, 40 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 97eddc83d19c..bf16edf2fcd9 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3947,4 +3947,7 @@ static inline void accept_memory(phys_addr_t start, phys_addr_t end)
 
 #endif
 
+int arch_get_shadow_stack_status(struct task_struct *t, unsigned long __user *status);
+int arch_set_shadow_stack_status(struct task_struct *t, unsigned long status);
+
 #endif /* _LINUX_MM_H */
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 3c36aeade991..9fdc77fa2bfe 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -305,4 +305,21 @@ struct prctl_mm_map {
 # define PR_RISCV_V_VSTATE_CTRL_NEXT_MASK	0xc
 # define PR_RISCV_V_VSTATE_CTRL_MASK		0x1f
 
+/*
+ * get shadow stack status for current thread. Assumes shadow stack is min 4 byte aligned.
+ * Note shadow stack can be 8 byte aligned on 64bit.
+ * Lower 2 bits can give status of locked and enabled/disabled.
+ * size and address range can be obtained via /proc/maps. get_shadow_stack_status will
+ * return base of shadow stack.
+ */
+#define PR_GET_SHADOW_STACK_STATUS      71
+/*
+ * set shadow stack status for current thread (including enabling, disabling or locking)
+ * note that it will only set the status and setup of the shadow stack. Allocating shadow
+ * stack should be done separately using mmap.
+ */
+#define PR_SET_SHADOW_STACK_STATUS      72
+# define PR_SHADOW_STACK_LOCK           (1UL << 0)
+# define PR_SHADOW_STACK_ENABLE         (1UL << 1)
+
 #endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index 05f838929e72..ebf9ea5f0fae 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2302,6 +2302,16 @@ int __weak arch_prctl_spec_ctrl_set(struct task_struct *t, unsigned long which,
 	return -EINVAL;
 }
 
+int __weak arch_get_shadow_stack_status(struct task_struct *t, unsigned long __user *status)
+{
+	return -EINVAL;
+}
+
+int __weak arch_set_shadow_stack_status(struct task_struct *t, unsigned long status)
+{
+	return -EINVAL;
+}
+
 #define PR_IO_FLUSHER (PF_MEMALLOC_NOIO | PF_LOCAL_THROTTLE)
 
 #ifdef CONFIG_ANON_VMA_NAME
@@ -2720,6 +2730,16 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 	case PR_RISCV_V_GET_CONTROL:
 		error = RISCV_V_GET_CONTROL();
 		break;
+	case PR_GET_SHADOW_STACK_STATUS:
+		if (arg3 || arg4 || arg5)
+			return -EINVAL;
+		error = arch_get_shadow_stack_status(me, (unsigned long __user *) arg2);
+		break;
+	case PR_SET_SHADOW_STACK_STATUS:
+		if (arg3 || arg4 || arg5)
+			return -EINVAL;
+		error = arch_set_shadow_stack_status(me, arg2);
+		break;
 	default:
 		error = -EINVAL;
 		break;

-- 
2.30.2