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, 102 insertions, 0 deletions

diff --git a/crypto/fips.c b/crypto/fips.c
new file mode 100644
index 000000000..c59711248
--- /dev/null
+++ b/crypto/fips.c
@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * FIPS 200 support.
+ *
+ * Copyright (c) 2008 Neil Horman <nhorman@tuxdriver.com>
+ */
+
+#include <linux/export.h>
+#include <linux/fips.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/sysctl.h>
+#include <linux/notifier.h>
+#include <linux/string_choices.h>
+#include <generated/utsrelease.h>
+
+int fips_enabled;
+EXPORT_SYMBOL_GPL(fips_enabled);
+
+ATOMIC_NOTIFIER_HEAD(fips_fail_notif_chain);
+EXPORT_SYMBOL_GPL(fips_fail_notif_chain);
+
+/* Process kernel command-line parameter at boot time. fips=0 or fips=1 */
+static int __init fips_enable(char *str)
+{
+	if (kstrtoint(str, 0, &fips_enabled))
+		return 0;
+
+	fips_enabled = !!fips_enabled;
+	pr_info("fips mode: %s\n", str_enabled_disabled(fips_enabled));
+	return 1;
+}
+
+__setup("fips=", fips_enable);
+
+#define FIPS_MODULE_NAME CONFIG_CRYPTO_FIPS_NAME
+#ifdef CONFIG_CRYPTO_FIPS_CUSTOM_VERSION
+#define FIPS_MODULE_VERSION CONFIG_CRYPTO_FIPS_VERSION
+#else
+#define FIPS_MODULE_VERSION UTS_RELEASE
+#endif
+
+static char fips_name[] = FIPS_MODULE_NAME;
+static char fips_version[] = FIPS_MODULE_VERSION;
+
+static const struct ctl_table crypto_sysctl_table[] = {
+	{
+		.procname	= "fips_enabled",
+		.data		= &fips_enabled,
+		.maxlen		= sizeof(int),
+		.mode		= 0444,
+		.proc_handler	= proc_dointvec
+	},
+	{
+		.procname	= "fips_name",
+		.data		= &fips_name,
+		.maxlen		= 64,
+		.mode		= 0444,
+		.proc_handler	= proc_dostring
+	},
+	{
+		.procname	= "fips_version",
+		.data		= &fips_version,
+		.maxlen		= 64,
+		.mode		= 0444,
+		.proc_handler	= proc_dostring
+	},
+};
+
+static struct ctl_table_header *crypto_sysctls;
+
+static void crypto_proc_fips_init(void)
+{
+	crypto_sysctls = register_sysctl("crypto", crypto_sysctl_table);
+}
+
+static void crypto_proc_fips_exit(void)
+{
+	unregister_sysctl_table(crypto_sysctls);
+}
+
+void fips_fail_notify(void)
+{
+	if (fips_enabled)
+		atomic_notifier_call_chain(&fips_fail_notif_chain, 0, NULL);
+}
+EXPORT_SYMBOL_GPL(fips_fail_notify);
+
+static int __init fips_init(void)
+{
+	crypto_proc_fips_init();
+	return 0;
+}
+
+static void __exit fips_exit(void)
+{
+	crypto_proc_fips_exit();
+}
+
+module_init(fips_init);
+module_exit(fips_exit);