[PATCH v3 3/6] exit: Expose "oops_count" to sysfs

[Kees Cook]

Since Oops count is now tracked and is a fairly interesting signal, add
the entry /sys/kernel/oops_count to expose it to userspace.

Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Reviewed-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 .../ABI/testing/sysfs-kernel-oops_count       |  6 +++++
 MAINTAINERS                                   |  1 +
 kernel/exit.c                                 | 22 +++++++++++++++++--
 3 files changed, 27 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-kernel-oops_count

diff --git a/Documentation/ABI/testing/sysfs-kernel-oops_count b/Documentation/ABI/testing/sysfs-kernel-oops_count
new file mode 100644
index 000000000000..156cca9dbc96
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-kernel-oops_count
@@ -0,0 +1,6 @@
+What:		/sys/kernel/oops_count
+Date:		November 2022
+KernelVersion:	6.2.0
+Contact:	Linux Kernel Hardening List <linux-hardening@xxxxxxxxxxxxxxx>
+Description:
+		Shows how many times the system has Oopsed since last boot.
diff --git a/MAINTAINERS b/MAINTAINERS
index 1cd80c113721..0a1e95a58e54 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -11106,6 +11106,7 @@ M:	Kees Cook <keescook@xxxxxxxxxxxx>
 L:	linux-hardening@xxxxxxxxxxxxxxx
 S:	Supported
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/hardening
+F:	Documentation/ABI/testing/sysfs-kernel-oops_count
 F:	include/linux/overflow.h
 F:	include/linux/randomize_kstack.h
 F:	mm/usercopy.c
diff --git a/kernel/exit.c b/kernel/exit.c
index 799c5edd6be6..bc62bfe75bc7 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -67,6 +67,7 @@
 #include <linux/io_uring.h>
 #include <linux/kprobes.h>
 #include <linux/rethook.h>
+#include <linux/sysfs.h>
 
 #include <linux/uaccess.h>
 #include <asm/unistd.h>
@@ -99,6 +100,25 @@ static __init int kernel_exit_sysctls_init(void)
 late_initcall(kernel_exit_sysctls_init);
 #endif
 
+static atomic_t oops_count = ATOMIC_INIT(0);
+
+#ifdef CONFIG_SYSFS
+static ssize_t oops_count_show(struct kobject *kobj, struct kobj_attribute *attr,
+			       char *page)
+{
+	return sysfs_emit(page, "%d\n", atomic_read(&oops_count));
+}
+
+static struct kobj_attribute oops_count_attr = __ATTR_RO(oops_count);
+
+static __init int kernel_exit_sysfs_init(void)
+{
+	sysfs_add_file_to_group(kernel_kobj, &oops_count_attr.attr, NULL);
+	return 0;
+}
+late_initcall(kernel_exit_sysfs_init);
+#endif
+
 static void __unhash_process(struct task_struct *p, bool group_dead)
 {
 	nr_threads--;
@@ -901,8 +921,6 @@ void __noreturn do_exit(long code)
 
 void __noreturn make_task_dead(int signr)
 {
-	static atomic_t oops_count = ATOMIC_INIT(0);
-
 	/*
 	 * Take the task off the cpu after something catastrophic has
 	 * happened.
-- 
2.34.1