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Message-Id: <20221114-disable-kexec-reset-v3-3-4ef4e929adf6@chromium.org>
Date: Tue, 20 Dec 2022 23:05:45 +0100
From: Ricardo Ribalda <ribalda@...omium.org>
To: Philipp Rudo <prudo@...hat.com>,
Eric Biederman <ebiederm@...ssion.com>,
Jonathan Corbet <corbet@....net>,
"Guilherme G. Piccoli" <gpiccoli@...lia.com>
Cc: linux-doc@...r.kernel.org,
Sergey Senozhatsky <senozhatsky@...omium.org>,
Steven Rostedt <rostedt@...dmis.org>,
linux-kernel@...r.kernel.org,
"Joel Fernandes (Google)" <joel@...lfernandes.org>,
Ricardo Ribalda <ribalda@...omium.org>,
Ross Zwisler <zwisler@...nel.org>, kexec@...ts.infradead.org
Subject: [PATCH v3 3/3] kexec: Introduce parameters load_limit_reboot and
load_limit_panic
Add two parameter to specify how many times a kexec kernel can be loaded.
The sysadmin can set different limits for kexec panic and kexec reboot
kernels.
The value can be modified at runtime via sysfs, but only with a value
smaller than the current one (except -1).
Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
---
Documentation/admin-guide/kernel-parameters.txt | 14 ++++
include/linux/kexec.h | 2 +-
kernel/kexec.c | 2 +-
kernel/kexec_core.c | 91 ++++++++++++++++++++++++-
kernel/kexec_file.c | 2 +-
5 files changed, 106 insertions(+), 5 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 42af9ca0127e..2b37d6a20747 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2374,6 +2374,20 @@
for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
are exclusive, so you cannot specify multiple forms.
+ kexec_core.load_limit_reboot=
+ kexec_core.load_limit_panic=
+ [KNL]
+ This parameter specifies a limit to the number of times
+ a kexec kernel can be loaded.
+ Format: <int>
+ -1 = Unlimited.
+ int = Number of times kexec can be called.
+
+ During runtime, this parameter can be modified with a
+ value smaller than the current one (but not -1).
+
+ Default: -1
+
kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
Format: <Controller#>[,poll interval]
The controller # is the number of the ehci usb debug
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 182e0c11b87b..5daf9990d5b8 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -407,7 +407,7 @@ extern int kimage_crash_copy_vmcoreinfo(struct kimage *image);
extern struct kimage *kexec_image;
extern struct kimage *kexec_crash_image;
-bool kexec_load_permitted(void);
+bool kexec_load_permitted(bool crash_image);
#ifndef kexec_flush_icache_page
#define kexec_flush_icache_page(page)
diff --git a/kernel/kexec.c b/kernel/kexec.c
index ce1bca874a8d..7aefd134e319 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -193,7 +193,7 @@ static inline int kexec_load_check(unsigned long nr_segments,
int result;
/* We only trust the superuser with rebooting the system. */
- if (!kexec_load_permitted())
+ if (!kexec_load_permitted(flags & KEXEC_ON_CRASH))
return -EPERM;
/* Permit LSMs and IMA to fail the kexec */
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index a1efc70f4158..adf71f2be3ff 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -952,13 +952,100 @@ static int __init kexec_core_sysctl_init(void)
late_initcall(kexec_core_sysctl_init);
#endif
-bool kexec_load_permitted(void)
+struct kexec_load_limit {
+ /* Mutex protects the limit count. */
+ struct mutex mutex;
+ int limit;
+};
+
+struct kexec_load_limit load_limit_reboot = {
+ .mutex = __MUTEX_INITIALIZER(load_limit_reboot.mutex),
+ .limit = -1,
+};
+
+struct kexec_load_limit load_limit_panic = {
+ .mutex = __MUTEX_INITIALIZER(load_limit_panic.mutex),
+ .limit = -1,
+};
+
+static int param_get_limit(char *buffer, const struct kernel_param *kp)
{
+ int ret;
+ struct kexec_load_limit *limit = kp->arg;
+
+ mutex_lock(&limit->mutex);
+ ret = scnprintf(buffer, PAGE_SIZE, "%i\n", limit->limit);
+ mutex_unlock(&limit->mutex);
+
+ return ret;
+}
+
+static int param_set_limit(const char *buffer, const struct kernel_param *kp)
+{
+ int ret;
+ struct kexec_load_limit *limit = kp->arg;
+ int new_val;
+
+ ret = kstrtoint(buffer, 0, &new_val);
+ if (ret)
+ return ret;
+
+ new_val = max(-1, new_val);
+
+ mutex_lock(&limit->mutex);
+
+ if (new_val == -1 && limit->limit != -1) {
+ ret = -EINVAL;
+ goto done;
+ }
+
+ if (limit->limit != -1 && new_val > limit->limit) {
+ ret = -EINVAL;
+ goto done;
+ }
+
+ limit->limit = new_val;
+
+done:
+ mutex_unlock(&limit->mutex);
+
+ return ret;
+}
+
+static const struct kernel_param_ops load_limit_ops = {
+ .get = param_get_limit,
+ .set = param_set_limit,
+};
+
+module_param_cb(load_limit_reboot, &load_limit_ops, &load_limit_reboot, 0644);
+MODULE_PARM_DESC(load_limit_reboot, "Maximum attempts to load a kexec reboot kernel");
+
+module_param_cb(load_limit_panic, &load_limit_ops, &load_limit_panic, 0644);
+MODULE_PARM_DESC(load_limit_reboot, "Maximum attempts to load a kexec panic kernel");
+
+bool kexec_load_permitted(bool crash_image)
+{
+ struct kexec_load_limit *limit;
+
/*
* Only the superuser can use the kexec syscall and if it has not
* been disabled.
*/
- return capable(CAP_SYS_BOOT) && !kexec_load_disabled;
+ if (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
+ return false;
+
+ /* Check limit counter and decrease it.*/
+ limit = crash_image ? &load_limit_panic : &load_limit_reboot;
+ mutex_lock(&limit->mutex);
+ if (!limit->limit) {
+ mutex_unlock(&limit->mutex);
+ return false;
+ }
+ if (limit->limit != -1)
+ limit->limit--;
+ mutex_unlock(&limit->mutex);
+
+ return true;
}
/*
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 29efa43ea951..6a1d4b07635e 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -330,7 +330,7 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
struct kimage **dest_image, *image;
/* We only trust the superuser with rebooting the system. */
- if (!kexec_load_permitted())
+ if (!kexec_load_permitted(flags & KEXEC_FILE_FLAGS))
return -EPERM;
/* Make sure we have a legal set of flags */
--
2.39.0.314.g84b9a713c41-goog-b4-0.11.0-dev-696ae
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