1 files changed, 88 insertions, 52 deletions
diff --git a/kernel/rseq.c b/kernel/rseq.c
index 2cb16091ec0a..b7a1ec327e81 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -78,24 +78,24 @@ efault:
 	return -EFAULT;
 }
 
-static void rseq_set_ro_fields(struct task_struct *t, u32 cpu_id_start, u32 cpu_id,
-			       u32 node_id, u32 mm_cid)
-{
-	rseq_kernel_fields(t)->cpu_id_start = cpu_id;
-	rseq_kernel_fields(t)->cpu_id = cpu_id;
-	rseq_kernel_fields(t)->node_id = node_id;
-	rseq_kernel_fields(t)->mm_cid = mm_cid;
-}
+/*
+ * Update an rseq field and its in-kernel copy in lock-step to keep a coherent
+ * state.
+ */
+#define rseq_unsafe_put_user(t, value, field, error_label)		\
+	do {								\
+		unsafe_put_user(value, &t->rseq->field, error_label);	\
+		rseq_kernel_fields(t)->field = value;			\
+	} while (0)
+
 #else
 static int rseq_validate_ro_fields(struct task_struct *t)
 {
 	return 0;
 }
 
-static void rseq_set_ro_fields(struct task_struct *t, u32 cpu_id_start, u32 cpu_id,
-			       u32 node_id, u32 mm_cid)
-{
-}
+#define rseq_unsafe_put_user(t, value, field, error_label)		\
+	unsafe_put_user(value, &t->rseq->field, error_label)
 #endif
 
 /*
@@ -173,17 +173,18 @@ static int rseq_update_cpu_node_id(struct task_struct *t)
 	WARN_ON_ONCE((int) mm_cid < 0);
 	if (!user_write_access_begin(rseq, t->rseq_len))
 		goto efault;
-	unsafe_put_user(cpu_id, &rseq->cpu_id_start, efault_end);
-	unsafe_put_user(cpu_id, &rseq->cpu_id, efault_end);
-	unsafe_put_user(node_id, &rseq->node_id, efault_end);
-	unsafe_put_user(mm_cid, &rseq->mm_cid, efault_end);
+
+	rseq_unsafe_put_user(t, cpu_id, cpu_id_start, efault_end);
+	rseq_unsafe_put_user(t, cpu_id, cpu_id, efault_end);
+	rseq_unsafe_put_user(t, node_id, node_id, efault_end);
+	rseq_unsafe_put_user(t, mm_cid, mm_cid, efault_end);
+
 	/*
 	 * Additional feature fields added after ORIG_RSEQ_SIZE
 	 * need to be conditionally updated only if
 	 * t->rseq_len != ORIG_RSEQ_SIZE.
 	 */
 	user_write_access_end();
-	rseq_set_ro_fields(t, cpu_id, cpu_id, node_id, mm_cid);
 	trace_rseq_update(t);
 	return 0;
 
@@ -195,6 +196,7 @@ efault:
 
 static int rseq_reset_rseq_cpu_node_id(struct task_struct *t)
 {
+	struct rseq __user *rseq = t->rseq;
 	u32 cpu_id_start = 0, cpu_id = RSEQ_CPU_ID_UNINITIALIZED, node_id = 0,
 	    mm_cid = 0;
 
@@ -202,40 +204,61 @@ static int rseq_reset_rseq_cpu_node_id(struct task_struct *t)
 	 * Validate read-only rseq fields.
 	 */
 	if (rseq_validate_ro_fields(t))
-		return -EFAULT;
-	/*
-	 * Reset cpu_id_start to its initial state (0).
-	 */
-	if (put_user(cpu_id_start, &t->rseq->cpu_id_start))
-		return -EFAULT;
-	/*
-	 * Reset cpu_id to RSEQ_CPU_ID_UNINITIALIZED, so any user coming
-	 * in after unregistration can figure out that rseq needs to be
-	 * registered again.
-	 */
-	if (put_user(cpu_id, &t->rseq->cpu_id))
-		return -EFAULT;
-	/*
-	 * Reset node_id to its initial state (0).
-	 */
-	if (put_user(node_id, &t->rseq->node_id))
-		return -EFAULT;
+		goto efault;
+
+	if (!user_write_access_begin(rseq, t->rseq_len))
+		goto efault;
+
 	/*
-	 * Reset mm_cid to its initial state (0).
+	 * Reset all fields to their initial state.
+	 *
+	 * All fields have an initial state of 0 except cpu_id which is set to
+	 * RSEQ_CPU_ID_UNINITIALIZED, so that any user coming in after
+	 * unregistration can figure out that rseq needs to be registered
+	 * again.
 	 */
-	if (put_user(mm_cid, &t->rseq->mm_cid))
-		return -EFAULT;
-
-	rseq_set_ro_fields(t, cpu_id_start, cpu_id, node_id, mm_cid);
+	rseq_unsafe_put_user(t, cpu_id_start, cpu_id_start, efault_end);
+	rseq_unsafe_put_user(t, cpu_id, cpu_id, efault_end);
+	rseq_unsafe_put_user(t, node_id, node_id, efault_end);
+	rseq_unsafe_put_user(t, mm_cid, mm_cid, efault_end);
 
 	/*
 	 * Additional feature fields added after ORIG_RSEQ_SIZE
 	 * need to be conditionally reset only if
 	 * t->rseq_len != ORIG_RSEQ_SIZE.
 	 */
+	user_write_access_end();
+	return 0;
+
+efault_end:
+	user_write_access_end();
+efault:
+	return -EFAULT;
+}
+
+/*
+ * Get the user-space pointer value stored in the 'rseq_cs' field.
+ */
+static int rseq_get_rseq_cs_ptr_val(struct rseq __user *rseq, u64 *rseq_cs)
+{
+	if (!rseq_cs)
+		return -EFAULT;
+
+#ifdef CONFIG_64BIT
+	if (get_user(*rseq_cs, &rseq->rseq_cs))
+		return -EFAULT;
+#else
+	if (copy_from_user(rseq_cs, &rseq->rseq_cs, sizeof(*rseq_cs)))
+		return -EFAULT;
+#endif
+
 	return 0;
 }
 
+/*
+ * If the rseq_cs field of 'struct rseq' contains a valid pointer to
+ * user-space, copy 'struct rseq_cs' from user-space and validate its fields.
+ */
 static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)
 {
 	struct rseq_cs __user *urseq_cs;
@@ -244,17 +267,16 @@ static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)
 	u32 sig;
 	int ret;
 
-#ifdef CONFIG_64BIT
-	if (get_user(ptr, &t->rseq->rseq_cs))
-		return -EFAULT;
-#else
-	if (copy_from_user(&ptr, &t->rseq->rseq_cs, sizeof(ptr)))
-		return -EFAULT;
-#endif
+	ret = rseq_get_rseq_cs_ptr_val(t->rseq, &ptr);
+	if (ret)
+		return ret;
+
+	/* If the rseq_cs pointer is NULL, return a cleared struct rseq_cs. */
 	if (!ptr) {
 		memset(rseq_cs, 0, sizeof(*rseq_cs));
 		return 0;
 	}
+	/* Check that the pointer value fits in the user-space process space. */
 	if (ptr >= TASK_SIZE)
 		return -EINVAL;
 	urseq_cs = (struct rseq_cs __user *)(unsigned long)ptr;
@@ -330,7 +352,7 @@ static int rseq_need_restart(struct task_struct *t, u32 cs_flags)
 	return !!event_mask;
 }
 
-static int clear_rseq_cs(struct task_struct *t)
+static int clear_rseq_cs(struct rseq __user *rseq)
 {
 	/*
 	 * The rseq_cs field is set to NULL on preemption or signal
@@ -341,9 +363,9 @@ static int clear_rseq_cs(struct task_struct *t)
 	 * Set rseq_cs to NULL.
 	 */
 #ifdef CONFIG_64BIT
-	return put_user(0UL, &t->rseq->rseq_cs);
+	return put_user(0UL, &rseq->rseq_cs);
 #else
-	if (clear_user(&t->rseq->rseq_cs, sizeof(t->rseq->rseq_cs)))
+	if (clear_user(&rseq->rseq_cs, sizeof(rseq->rseq_cs)))
 		return -EFAULT;
 	return 0;
 #endif
@@ -375,11 +397,11 @@ static int rseq_ip_fixup(struct pt_regs *regs)
 	 * Clear the rseq_cs pointer and return.
 	 */
 	if (!in_rseq_cs(ip, &rseq_cs))
-		return clear_rseq_cs(t);
+		return clear_rseq_cs(t->rseq);
 	ret = rseq_need_restart(t, rseq_cs.flags);
 	if (ret <= 0)
 		return ret;
-	ret = clear_rseq_cs(t);
+	ret = clear_rseq_cs(t->rseq);
 	if (ret)
 		return ret;
 	trace_rseq_ip_fixup(ip, rseq_cs.start_ip, rseq_cs.post_commit_offset,
@@ -453,6 +475,7 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len,
 		int, flags, u32, sig)
 {
 	int ret;
+	u64 rseq_cs;
 
 	if (flags & RSEQ_FLAG_UNREGISTER) {
 		if (flags & ~RSEQ_FLAG_UNREGISTER)
@@ -507,6 +530,19 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len,
 		return -EINVAL;
 	if (!access_ok(rseq, rseq_len))
 		return -EFAULT;
+
+	/*
+	 * If the rseq_cs pointer is non-NULL on registration, clear it to
+	 * avoid a potential segfault on return to user-space. The proper thing
+	 * to do would have been to fail the registration but this would break
+	 * older libcs that reuse the rseq area for new threads without
+	 * clearing the fields.
+	 */
+	if (rseq_get_rseq_cs_ptr_val(rseq, &rseq_cs))
+	        return -EFAULT;
+	if (rseq_cs && clear_rseq_cs(rseq))
+		return -EFAULT;
+
 #ifdef CONFIG_DEBUG_RSEQ
 	/*
 	 * Initialize the in-kernel rseq fields copy for validation of