ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faultsgrafted

When CONFIG_DEBUG_USER=y, and cmdline "user_debug=31" is set,
a user fault may trigger show_pte() without any lock.
If another thread in the same process concurrently calls munmap(),
the page table pages may be freed while show_pte() is still traversing
them, causing a use-after-free in show_pte().

If CONFIG_ARM_LPAE=y, this may cause a kernel panic if the pages table
of PMD are freed when show_pte() is running.

Acquire mmap_write_lock() around show_pte() for user faults to fix the
contention.

For user faults, additionally restrict that show_pte() is called only
when the addr is a user-space address (addr < TASK_SIZE). This is because
the lock of tsk->mm only protects the virtual memory of user address space,
furthermore, dumping the page tables of a kernel-space address for user
faults is unnecessary and may have security implications.

Keep everything unchanged for kernel faults, because the kernel is
already in the "oops" state, acquiring a lock may risk a deadlock.

Co-developed-by: Qi Xi <xiqi2@huawei.com>

Fixes: 6d021b724481 ("ARM: dump pgd, pmd and pte states on unhandled data abort faults")
Link: https://lore.kernel.org/20260716014022.2823-1-xieyuanbin1@huawei.com
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Qi Xi <xiqi2@huawei.com>
Signed-off-by: Xie Yuanbin <xieyuanbin1@huawei.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 246 insertions, 0 deletions

diff --git a/security/ipe/fs.c b/security/ipe/fs.c
new file mode 100644
index 000000000..076c111c8
--- /dev/null
+++ b/security/ipe/fs.c
@@ -0,0 +1,246 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020-2024 Microsoft Corporation. All rights reserved.
+ */
+
+#include <linux/dcache.h>
+#include <linux/security.h>
+
+#include "ipe.h"
+#include "fs.h"
+#include "eval.h"
+#include "policy.h"
+#include "audit.h"
+
+static struct dentry *root __ro_after_init;
+struct dentry *policy_root __ro_after_init;
+
+/**
+ * setaudit() - Write handler for the securityfs node, "ipe/success_audit"
+ * @f: Supplies a file structure representing the securityfs node.
+ * @data: Supplies a buffer passed to the write syscall.
+ * @len: Supplies the length of @data.
+ * @offset: unused.
+ *
+ * Return:
+ * * Length of buffer written	- Success
+ * * %-EPERM			- Insufficient permission
+ */
+static ssize_t setaudit(struct file *f, const char __user *data,
+			size_t len, loff_t *offset)
+{
+	int rc = 0;
+	bool value;
+
+	if (!file_ns_capable(f, &init_user_ns, CAP_MAC_ADMIN))
+		return -EPERM;
+
+	rc = kstrtobool_from_user(data, len, &value);
+	if (rc)
+		return rc;
+
+	WRITE_ONCE(success_audit, value);
+
+	return len;
+}
+
+/**
+ * getaudit() - Read handler for the securityfs node, "ipe/success_audit"
+ * @f: Supplies a file structure representing the securityfs node.
+ * @data: Supplies a buffer passed to the read syscall.
+ * @len: Supplies the length of @data.
+ * @offset: unused.
+ *
+ * Return: Length of buffer written
+ */
+static ssize_t getaudit(struct file *f, char __user *data,
+			size_t len, loff_t *offset)
+{
+	const char *result;
+
+	result = ((READ_ONCE(success_audit)) ? "1" : "0");
+
+	return simple_read_from_buffer(data, len, offset, result, 1);
+}
+
+/**
+ * setenforce() - Write handler for the securityfs node, "ipe/enforce"
+ * @f: Supplies a file structure representing the securityfs node.
+ * @data: Supplies a buffer passed to the write syscall.
+ * @len: Supplies the length of @data.
+ * @offset: unused.
+ *
+ * Return:
+ * * Length of buffer written	- Success
+ * * %-EPERM			- Insufficient permission
+ */
+static ssize_t setenforce(struct file *f, const char __user *data,
+			  size_t len, loff_t *offset)
+{
+	int rc = 0;
+	bool new_value, old_value;
+
+	if (!file_ns_capable(f, &init_user_ns, CAP_MAC_ADMIN))
+		return -EPERM;
+
+	old_value = READ_ONCE(enforce);
+	rc = kstrtobool_from_user(data, len, &new_value);
+	if (rc)
+		return rc;
+
+	if (new_value != old_value) {
+		ipe_audit_enforce(new_value, old_value);
+		WRITE_ONCE(enforce, new_value);
+	}
+
+	return len;
+}
+
+/**
+ * getenforce() - Read handler for the securityfs node, "ipe/enforce"
+ * @f: Supplies a file structure representing the securityfs node.
+ * @data: Supplies a buffer passed to the read syscall.
+ * @len: Supplies the length of @data.
+ * @offset: unused.
+ *
+ * Return: Length of buffer written
+ */
+static ssize_t getenforce(struct file *f, char __user *data,
+			  size_t len, loff_t *offset)
+{
+	const char *result;
+
+	result = ((READ_ONCE(enforce)) ? "1" : "0");
+
+	return simple_read_from_buffer(data, len, offset, result, 1);
+}
+
+/**
+ * new_policy() - Write handler for the securityfs node, "ipe/new_policy".
+ * @f: Supplies a file structure representing the securityfs node.
+ * @data: Supplies a buffer passed to the write syscall.
+ * @len: Supplies the length of @data.
+ * @offset: unused.
+ *
+ * Return:
+ * * Length of buffer written	- Success
+ * * %-EPERM			- Insufficient permission
+ * * %-ENOMEM			- Out of memory (OOM)
+ * * %-EBADMSG			- Policy is invalid
+ * * %-ERANGE			- Policy version number overflow
+ * * %-EINVAL			- Policy version parsing error
+ * * %-EEXIST			- Same name policy already deployed
+ * * %-ENOKEY			- Policy signing key not found
+ * * %-EKEYREJECTED		- Policy signature verification failed
+ */
+static ssize_t new_policy(struct file *f, const char __user *data,
+			  size_t len, loff_t *offset)
+{
+	struct ipe_policy *p = NULL;
+	char *copy = NULL;
+	int rc = 0;
+
+	if (!file_ns_capable(f, &init_user_ns, CAP_MAC_ADMIN)) {
+		rc = -EPERM;
+		goto out;
+	}
+
+	copy = memdup_user_nul(data, len);
+	if (IS_ERR(copy)) {
+		rc = PTR_ERR(copy);
+		copy = NULL;
+		goto out;
+	}
+
+	p = ipe_new_policy(NULL, 0, copy, len);
+	if (IS_ERR(p)) {
+		rc = PTR_ERR(p);
+		goto out;
+	}
+
+	rc = ipe_new_policyfs_node(p);
+	if (rc)
+		goto out;
+
+out:
+	kfree(copy);
+	if (rc < 0) {
+		ipe_free_policy(p);
+		ipe_audit_policy_load(ERR_PTR(rc));
+	} else {
+		ipe_audit_policy_load(p);
+	}
+	return (rc < 0) ? rc : len;
+}
+
+static const struct file_operations np_fops = {
+	.write = new_policy,
+};
+
+static const struct file_operations audit_fops = {
+	.write = setaudit,
+	.read = getaudit,
+};
+
+static const struct file_operations enforce_fops = {
+	.write = setenforce,
+	.read = getenforce,
+};
+
+/**
+ * ipe_init_securityfs() - Initialize IPE's securityfs tree at fsinit.
+ *
+ * Return: %0 on success. If an error occurs, the function will return
+ * the -errno.
+ */
+int __init ipe_init_securityfs(void)
+{
+	int rc = 0;
+	struct ipe_policy *ap;
+	struct dentry *dentry;
+
+	if (!ipe_enabled)
+		return -EOPNOTSUPP;
+
+	root = securityfs_create_dir("ipe", NULL);
+	if (IS_ERR(root))
+		return PTR_ERR(root);
+
+	dentry = securityfs_create_file("success_audit", 0600, root,
+					    NULL, &audit_fops);
+	if (IS_ERR(dentry)) {
+		rc = PTR_ERR(dentry);
+		goto err;
+	}
+
+	dentry = securityfs_create_file("enforce", 0600, root, NULL,
+					      &enforce_fops);
+	if (IS_ERR(dentry)) {
+		rc = PTR_ERR(dentry);
+		goto err;
+	}
+
+	policy_root = securityfs_create_dir("policies", root);
+	if (IS_ERR(policy_root)) {
+		rc = PTR_ERR(policy_root);
+		goto err;
+	}
+
+	ap = rcu_access_pointer(ipe_active_policy);
+	if (ap) {
+		rc = ipe_new_policyfs_node(ap);
+		if (rc)
+			goto err;
+	}
+
+	dentry = securityfs_create_file("new_policy", 0200, root, NULL, &np_fops);
+	if (IS_ERR(dentry)) {
+		rc = PTR_ERR(dentry);
+		goto err;
+	}
+
+	return 0;
+err:
+	securityfs_remove(root);
+	return rc;
+}