[PATCH v4 0/3] kexec: Add new parameter to limit the access to kexec

[PATCH v4 0/3] kexec: Add new parameter to limit the access to kexec

[Ricardo Ribalda]

Add two parameter to specify how many times a kexec kernel can be loaded.

These parameter allow hardening the system.

While we are at it, fix a documentation issue and refactor some code.

To: Jonathan Corbet <corbet@lwn.net>
To: Eric Biederman <ebiederm@xmission.com>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: kexec@lists.infradead.org
Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ross Zwisler <zwisler@kernel.org>
To: Philipp Rudo <prudo@redhat.com>
To: Guilherme G. Piccoli <gpiccoli@igalia.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>

---
Changes in v4 (Thanks Steven!):
- Uses sysctl instead or module_parameters
- Pass image type instead of boolean to permitted
- Fix typo on flag handling
- Return -EINVAL for values that does not change the current value.
- Link to v3: https://lore.kernel.org/r/20221114-disable-kexec-reset-v3-0-4ef4e929adf6@chromium.org

Changes in v3:
- s/paramter/parameter/ Thanks Ghilherme!
- s/permited/permitted/ Thanks Joel!
- Link to v2: https://lore.kernel.org/r/20221114-disable-kexec-reset-v2-0-c498313c1bb5@chromium.org

Changes in v2:
- Instead of kexec_reboot_disabled, add two new counters (Thanks Philipp!)
- Link to v1: https://lore.kernel.org/r/20221114-disable-kexec-reset-v1-0-fb51d20cf871@chromium.org

---
Ricardo Ribalda (3):
      Documentation: sysctl: Correct kexec_load_disabled
      kexec: Factor out kexec_load_permitted
      kexec: Introduce sysctl parameters kexec_load_limit_*

 Documentation/admin-guide/sysctl/kernel.rst | 25 +++++++-
 include/linux/kexec.h                       |  3 +-
 kernel/kexec.c                              |  4 +-
 kernel/kexec_core.c                         | 96 ++++++++++++++++++++++++++++-
 kernel/kexec_file.c                         | 11 ++--
 5 files changed, 129 insertions(+), 10 deletions(-)
---
base-commit: 479174d402bcf60789106eedc4def3957c060bad
change-id: 20221114-disable-kexec-reset-19b7e117338f

Best regards,
-- 
Ricardo Ribalda <ribalda@chromium.org>

[PATCH v4 0/3] kexec: Add new parameter to limit the access to kexec

[Ricardo Ribalda]

Add two parameter to specify how many times a kexec kernel can be loaded.

These parameter allow hardening the system.

While we are at it, fix a documentation issue and refactor some code.

To: Jonathan Corbet <corbet@lwn.net>
To: Eric Biederman <ebiederm@xmission.com>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: kexec@lists.infradead.org
Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ross Zwisler <zwisler@kernel.org>
To: Philipp Rudo <prudo@redhat.com>
To: Guilherme G. Piccoli <gpiccoli@igalia.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>

---
Changes in v4 (Thanks Steven!):
- Uses sysctl instead or module_parameters
- Pass image type instead of boolean to permitted
- Fix typo on flag handling
- Return -EINVAL for values that does not change the current value.
- Link to v3: https://lore.kernel.org/r/20221114-disable-kexec-reset-v3-0-4ef4e929adf6@chromium.org

Changes in v3:
- s/paramter/parameter/ Thanks Ghilherme!
- s/permited/permitted/ Thanks Joel!
- Link to v2: https://lore.kernel.org/r/20221114-disable-kexec-reset-v2-0-c498313c1bb5@chromium.org

Changes in v2:
- Instead of kexec_reboot_disabled, add two new counters (Thanks Philipp!)
- Link to v1: https://lore.kernel.org/r/20221114-disable-kexec-reset-v1-0-fb51d20cf871@chromium.org

---
Ricardo Ribalda (3):
      Documentation: sysctl: Correct kexec_load_disabled
      kexec: Factor out kexec_load_permitted
      kexec: Introduce sysctl parameters kexec_load_limit_*

 Documentation/admin-guide/sysctl/kernel.rst | 25 +++++++-
 include/linux/kexec.h                       |  3 +-
 kernel/kexec.c                              |  4 +-
 kernel/kexec_core.c                         | 96 ++++++++++++++++++++++++++++-
 kernel/kexec_file.c                         | 11 ++--
 5 files changed, 129 insertions(+), 10 deletions(-)
---
base-commit: 479174d402bcf60789106eedc4def3957c060bad
change-id: 20221114-disable-kexec-reset-19b7e117338f

Best regards,
-- 
Ricardo Ribalda <ribalda@chromium.org>

_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

[PATCH v4 1/3] Documentation: sysctl: Correct kexec_load_disabled

[Ricardo Ribalda]

kexec_load_disabled affects both ``kexec_load`` and ``kexec_file_load``
syscalls. Make it explicit.

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
 Documentation/admin-guide/sysctl/kernel.rst | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 98d1b198b2b4..97394bd9d065 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -450,9 +450,10 @@ this allows system administrators to override the
 kexec_load_disabled
 ===================
 
-A toggle indicating if the ``kexec_load`` syscall has been disabled.
-This value defaults to 0 (false: ``kexec_load`` enabled), but can be
-set to 1 (true: ``kexec_load`` disabled).
+A toggle indicating if the syscalls ``kexec_load`` and
+``kexec_file_load`` have been disabled.
+This value defaults to 0 (false: ``kexec_*load`` enabled), but can be
+set to 1 (true: ``kexec_*load`` disabled).
 Once true, kexec can no longer be used, and the toggle cannot be set
 back to false.
 This allows a kexec image to be loaded before disabling the syscall,

-- 
2.39.0.314.g84b9a713c41-goog-b4-0.11.0-dev-696ae

[PATCH v4 1/3] Documentation: sysctl: Correct kexec_load_disabled

[Ricardo Ribalda]

kexec_load_disabled affects both ``kexec_load`` and ``kexec_file_load``
syscalls. Make it explicit.

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
 Documentation/admin-guide/sysctl/kernel.rst | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 98d1b198b2b4..97394bd9d065 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -450,9 +450,10 @@ this allows system administrators to override the
 kexec_load_disabled
 ===================
 
-A toggle indicating if the ``kexec_load`` syscall has been disabled.
-This value defaults to 0 (false: ``kexec_load`` enabled), but can be
-set to 1 (true: ``kexec_load`` disabled).
+A toggle indicating if the syscalls ``kexec_load`` and
+``kexec_file_load`` have been disabled.
+This value defaults to 0 (false: ``kexec_*load`` enabled), but can be
+set to 1 (true: ``kexec_*load`` disabled).
 Once true, kexec can no longer be used, and the toggle cannot be set
 back to false.
 This allows a kexec image to be loaded before disabling the syscall,

-- 
2.39.0.314.g84b9a713c41-goog-b4-0.11.0-dev-696ae

_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

[PATCH v4 2/3] kexec: Factor out kexec_load_permitted

[Ricardo Ribalda]

Both syscalls (kexec and kexec_file) do the same check, lets factor it
out.

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
 include/linux/kexec.h |  3 ++-
 kernel/kexec.c        |  2 +-
 kernel/kexec_core.c   | 11 ++++++++++-
 kernel/kexec_file.c   |  2 +-
 4 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 41a686996aaa..182e0c11b87b 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -406,7 +406,8 @@ extern int kimage_crash_copy_vmcoreinfo(struct kimage *image);
 
 extern struct kimage *kexec_image;
 extern struct kimage *kexec_crash_image;
-extern int kexec_load_disabled;
+
+bool kexec_load_permitted(void);
 
 #ifndef kexec_flush_icache_page
 #define kexec_flush_icache_page(page)
diff --git a/kernel/kexec.c b/kernel/kexec.c
index cb8e6e6f983c..ce1bca874a8d 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 (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
+	if (!kexec_load_permitted())
 		return -EPERM;
 
 	/* Permit LSMs and IMA to fail the kexec */
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index ca2743f9c634..a1efc70f4158 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -928,7 +928,7 @@ int kimage_load_segment(struct kimage *image,
 
 struct kimage *kexec_image;
 struct kimage *kexec_crash_image;
-int kexec_load_disabled;
+static int kexec_load_disabled;
 #ifdef CONFIG_SYSCTL
 static struct ctl_table kexec_core_sysctls[] = {
 	{
@@ -952,6 +952,15 @@ static int __init kexec_core_sysctl_init(void)
 late_initcall(kexec_core_sysctl_init);
 #endif
 
+bool kexec_load_permitted(void)
+{
+	/*
+	 * Only the superuser can use the kexec syscall and if it has not
+	 * been disabled.
+	 */
+	return capable(CAP_SYS_BOOT) && !kexec_load_disabled;
+}
+
 /*
  * No panic_cpu check version of crash_kexec().  This function is called
  * only when panic_cpu holds the current CPU number; this is the only CPU
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 45637511e0de..29efa43ea951 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 (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
+	if (!kexec_load_permitted())
 		return -EPERM;
 
 	/* Make sure we have a legal set of flags */

-- 
2.39.0.314.g84b9a713c41-goog-b4-0.11.0-dev-696ae

[PATCH v4 2/3] kexec: Factor out kexec_load_permitted

[Ricardo Ribalda]

Both syscalls (kexec and kexec_file) do the same check, lets factor it
out.

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
 include/linux/kexec.h |  3 ++-
 kernel/kexec.c        |  2 +-
 kernel/kexec_core.c   | 11 ++++++++++-
 kernel/kexec_file.c   |  2 +-
 4 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 41a686996aaa..182e0c11b87b 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -406,7 +406,8 @@ extern int kimage_crash_copy_vmcoreinfo(struct kimage *image);
 
 extern struct kimage *kexec_image;
 extern struct kimage *kexec_crash_image;
-extern int kexec_load_disabled;
+
+bool kexec_load_permitted(void);
 
 #ifndef kexec_flush_icache_page
 #define kexec_flush_icache_page(page)
diff --git a/kernel/kexec.c b/kernel/kexec.c
index cb8e6e6f983c..ce1bca874a8d 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 (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
+	if (!kexec_load_permitted())
 		return -EPERM;
 
 	/* Permit LSMs and IMA to fail the kexec */
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index ca2743f9c634..a1efc70f4158 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -928,7 +928,7 @@ int kimage_load_segment(struct kimage *image,
 
 struct kimage *kexec_image;
 struct kimage *kexec_crash_image;
-int kexec_load_disabled;
+static int kexec_load_disabled;
 #ifdef CONFIG_SYSCTL
 static struct ctl_table kexec_core_sysctls[] = {
 	{
@@ -952,6 +952,15 @@ static int __init kexec_core_sysctl_init(void)
 late_initcall(kexec_core_sysctl_init);
 #endif
 
+bool kexec_load_permitted(void)
+{
+	/*
+	 * Only the superuser can use the kexec syscall and if it has not
+	 * been disabled.
+	 */
+	return capable(CAP_SYS_BOOT) && !kexec_load_disabled;
+}
+
 /*
  * No panic_cpu check version of crash_kexec().  This function is called
  * only when panic_cpu holds the current CPU number; this is the only CPU
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 45637511e0de..29efa43ea951 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 (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
+	if (!kexec_load_permitted())
 		return -EPERM;
 
 	/* Make sure we have a legal set of flags */

-- 
2.39.0.314.g84b9a713c41-goog-b4-0.11.0-dev-696ae

_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

[PATCH v4 3/3] kexec: Introduce sysctl parameters kexec_load_limit_*

[Ricardo Ribalda]

Add two parameters 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 sysctl, but only with a value
smaller than the current one (except -1).

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
 Documentation/admin-guide/sysctl/kernel.rst | 18 ++++++
 include/linux/kexec.h                       |  2 +-
 kernel/kexec.c                              |  4 +-
 kernel/kexec_core.c                         | 89 ++++++++++++++++++++++++++++-
 kernel/kexec_file.c                         | 11 ++--
 5 files changed, 116 insertions(+), 8 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 97394bd9d065..a3922dffbd47 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -461,6 +461,24 @@ allowing a system to set up (and later use) an image without it being
 altered.
 Generally used together with the `modules_disabled`_ sysctl.
 
+kexec_load_limit_panic
+======================
+
+This parameter specifies a limit to the number of times the syscalls
+``kexec_load`` and ``kexec_file_load`` can be called with a crash
+image. It can only be set with a more restrictive value than the
+current one.
+
+=  =============================================================
+-1 Unlimited calls to kexec. This is the default setting.
+N  Number of calls left.
+=  =============================================================
+
+kexec_load_limit_reboot
+======================
+
+Similar functionality as ``kexec_load_limit_panic``, but for a crash
+image.
 
 kptr_restrict
 =============
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 182e0c11b87b..791e65829f86 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(int kexec_image_type);
 
 #ifndef kexec_flush_icache_page
 #define kexec_flush_icache_page(page)
diff --git a/kernel/kexec.c b/kernel/kexec.c
index ce1bca874a8d..92d301f98776 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -190,10 +190,12 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
 static inline int kexec_load_check(unsigned long nr_segments,
 				   unsigned long flags)
 {
+	int image_type = (flags & KEXEC_ON_CRASH) ?
+			 KEXEC_TYPE_CRASH : KEXEC_TYPE_DEFAULT;
 	int result;
 
 	/* We only trust the superuser with rebooting the system. */
-	if (!kexec_load_permitted())
+	if (!kexec_load_permitted(image_type))
 		return -EPERM;
 
 	/* Permit LSMs and IMA to fail the kexec */
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index a1efc70f4158..6131b1aee165 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -926,10 +926,64 @@ int kimage_load_segment(struct kimage *image,
 	return result;
 }
 
+struct kexec_load_limit {
+	/* Mutex protects the limit count. */
+	struct mutex mutex;
+	int limit;
+};
+
+static struct kexec_load_limit load_limit_reboot = {
+	.mutex = __MUTEX_INITIALIZER(load_limit_reboot.mutex),
+	.limit = -1,
+};
+
+static struct kexec_load_limit load_limit_panic = {
+	.mutex = __MUTEX_INITIALIZER(load_limit_panic.mutex),
+	.limit = -1,
+};
+
 struct kimage *kexec_image;
 struct kimage *kexec_crash_image;
 static int kexec_load_disabled;
+
 #ifdef CONFIG_SYSCTL
+static int kexec_limit_handler(struct ctl_table *table, int write,
+			       void *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct kexec_load_limit *limit = table->data;
+	int val;
+	struct ctl_table tmp = {
+		.data = &val,
+		.maxlen = sizeof(val),
+		.mode = table->mode,
+	};
+	int ret;
+
+	if (write) {
+		ret = proc_dointvec(&tmp, write, buffer, lenp, ppos);
+		if (ret)
+			return ret;
+
+		if (val < 0)
+			return -EINVAL;
+
+		mutex_lock(&limit->mutex);
+		if (limit->limit != -1 && val >= limit->limit)
+			ret = -EINVAL;
+		else
+			limit->limit = val;
+		mutex_unlock(&limit->mutex);
+
+		return ret;
+	}
+
+	mutex_lock(&limit->mutex);
+	val = limit->limit;
+	mutex_unlock(&limit->mutex);
+
+	return proc_dointvec(&tmp, write, buffer, lenp, ppos);
+}
+
 static struct ctl_table kexec_core_sysctls[] = {
 	{
 		.procname	= "kexec_load_disabled",
@@ -941,6 +995,20 @@ static struct ctl_table kexec_core_sysctls[] = {
 		.extra1		= SYSCTL_ONE,
 		.extra2		= SYSCTL_ONE,
 	},
+	{
+		.procname	= "kexec_load_limit_panic",
+		.data		= &load_limit_panic,
+		.maxlen		= sizeof(load_limit_panic),
+		.mode		= 0644,
+		.proc_handler	= kexec_limit_handler,
+	},
+	{
+		.procname	= "kexec_load_limit_reboot",
+		.data		= &load_limit_reboot,
+		.maxlen		= sizeof(load_limit_reboot),
+		.mode		= 0644,
+		.proc_handler	= kexec_limit_handler,
+	},
 	{ }
 };
 
@@ -952,13 +1020,30 @@ static int __init kexec_core_sysctl_init(void)
 late_initcall(kexec_core_sysctl_init);
 #endif
 
-bool kexec_load_permitted(void)
+bool kexec_load_permitted(int kexec_image_type)
 {
+	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 = (kexec_image_type == KEXEC_TYPE_CRASH) ?
+		&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..da9cfbbb0cbd 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -326,11 +326,13 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
 		unsigned long, cmdline_len, const char __user *, cmdline_ptr,
 		unsigned long, flags)
 {
-	int ret = 0, i;
+	int image_type = (flags & KEXEC_FILE_ON_CRASH) ?
+			 KEXEC_TYPE_CRASH : KEXEC_TYPE_DEFAULT;
 	struct kimage **dest_image, *image;
+	int ret = 0, i;
 
 	/* We only trust the superuser with rebooting the system. */
-	if (!kexec_load_permitted())
+	if (!kexec_load_permitted(flags & KEXEC_FILE_ON_CRASH))
 		return -EPERM;
 
 	/* Make sure we have a legal set of flags */
@@ -342,11 +344,12 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
 	if (!kexec_trylock())
 		return -EBUSY;
 
-	dest_image = &kexec_image;
-	if (flags & KEXEC_FILE_ON_CRASH) {
+	if (image_type == KEXEC_TYPE_CRASH) {
 		dest_image = &kexec_crash_image;
 		if (kexec_crash_image)
 			arch_kexec_unprotect_crashkres();
+	} else {
+		dest_image = &kexec_image;
 	}
 
 	if (flags & KEXEC_FILE_UNLOAD)

-- 
2.39.0.314.g84b9a713c41-goog-b4-0.11.0-dev-696ae

[PATCH v4 3/3] kexec: Introduce sysctl parameters kexec_load_limit_*

[Ricardo Ribalda]

Add two parameters 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 sysctl, but only with a value
smaller than the current one (except -1).

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
 Documentation/admin-guide/sysctl/kernel.rst | 18 ++++++
 include/linux/kexec.h                       |  2 +-
 kernel/kexec.c                              |  4 +-
 kernel/kexec_core.c                         | 89 ++++++++++++++++++++++++++++-
 kernel/kexec_file.c                         | 11 ++--
 5 files changed, 116 insertions(+), 8 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 97394bd9d065..a3922dffbd47 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -461,6 +461,24 @@ allowing a system to set up (and later use) an image without it being
 altered.
 Generally used together with the `modules_disabled`_ sysctl.
 
+kexec_load_limit_panic
+======================
+
+This parameter specifies a limit to the number of times the syscalls
+``kexec_load`` and ``kexec_file_load`` can be called with a crash
+image. It can only be set with a more restrictive value than the
+current one.
+
+=  =============================================================
+-1 Unlimited calls to kexec. This is the default setting.
+N  Number of calls left.
+=  =============================================================
+
+kexec_load_limit_reboot
+======================
+
+Similar functionality as ``kexec_load_limit_panic``, but for a crash
+image.
 
 kptr_restrict
 =============
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 182e0c11b87b..791e65829f86 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(int kexec_image_type);
 
 #ifndef kexec_flush_icache_page
 #define kexec_flush_icache_page(page)
diff --git a/kernel/kexec.c b/kernel/kexec.c
index ce1bca874a8d..92d301f98776 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -190,10 +190,12 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
 static inline int kexec_load_check(unsigned long nr_segments,
 				   unsigned long flags)
 {
+	int image_type = (flags & KEXEC_ON_CRASH) ?
+			 KEXEC_TYPE_CRASH : KEXEC_TYPE_DEFAULT;
 	int result;
 
 	/* We only trust the superuser with rebooting the system. */
-	if (!kexec_load_permitted())
+	if (!kexec_load_permitted(image_type))
 		return -EPERM;
 
 	/* Permit LSMs and IMA to fail the kexec */
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index a1efc70f4158..6131b1aee165 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -926,10 +926,64 @@ int kimage_load_segment(struct kimage *image,
 	return result;
 }
 
+struct kexec_load_limit {
+	/* Mutex protects the limit count. */
+	struct mutex mutex;
+	int limit;
+};
+
+static struct kexec_load_limit load_limit_reboot = {
+	.mutex = __MUTEX_INITIALIZER(load_limit_reboot.mutex),
+	.limit = -1,
+};
+
+static struct kexec_load_limit load_limit_panic = {
+	.mutex = __MUTEX_INITIALIZER(load_limit_panic.mutex),
+	.limit = -1,
+};
+
 struct kimage *kexec_image;
 struct kimage *kexec_crash_image;
 static int kexec_load_disabled;
+
 #ifdef CONFIG_SYSCTL
+static int kexec_limit_handler(struct ctl_table *table, int write,
+			       void *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct kexec_load_limit *limit = table->data;
+	int val;
+	struct ctl_table tmp = {
+		.data = &val,
+		.maxlen = sizeof(val),
+		.mode = table->mode,
+	};
+	int ret;
+
+	if (write) {
+		ret = proc_dointvec(&tmp, write, buffer, lenp, ppos);
+		if (ret)
+			return ret;
+
+		if (val < 0)
+			return -EINVAL;
+
+		mutex_lock(&limit->mutex);
+		if (limit->limit != -1 && val >= limit->limit)
+			ret = -EINVAL;
+		else
+			limit->limit = val;
+		mutex_unlock(&limit->mutex);
+
+		return ret;
+	}
+
+	mutex_lock(&limit->mutex);
+	val = limit->limit;
+	mutex_unlock(&limit->mutex);
+
+	return proc_dointvec(&tmp, write, buffer, lenp, ppos);
+}
+
 static struct ctl_table kexec_core_sysctls[] = {
 	{
 		.procname	= "kexec_load_disabled",
@@ -941,6 +995,20 @@ static struct ctl_table kexec_core_sysctls[] = {
 		.extra1		= SYSCTL_ONE,
 		.extra2		= SYSCTL_ONE,
 	},
+	{
+		.procname	= "kexec_load_limit_panic",
+		.data		= &load_limit_panic,
+		.maxlen		= sizeof(load_limit_panic),
+		.mode		= 0644,
+		.proc_handler	= kexec_limit_handler,
+	},
+	{
+		.procname	= "kexec_load_limit_reboot",
+		.data		= &load_limit_reboot,
+		.maxlen		= sizeof(load_limit_reboot),
+		.mode		= 0644,
+		.proc_handler	= kexec_limit_handler,
+	},
 	{ }
 };
 
@@ -952,13 +1020,30 @@ static int __init kexec_core_sysctl_init(void)
 late_initcall(kexec_core_sysctl_init);
 #endif
 
-bool kexec_load_permitted(void)
+bool kexec_load_permitted(int kexec_image_type)
 {
+	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 = (kexec_image_type == KEXEC_TYPE_CRASH) ?
+		&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..da9cfbbb0cbd 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -326,11 +326,13 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
 		unsigned long, cmdline_len, const char __user *, cmdline_ptr,
 		unsigned long, flags)
 {
-	int ret = 0, i;
+	int image_type = (flags & KEXEC_FILE_ON_CRASH) ?
+			 KEXEC_TYPE_CRASH : KEXEC_TYPE_DEFAULT;
 	struct kimage **dest_image, *image;
+	int ret = 0, i;
 
 	/* We only trust the superuser with rebooting the system. */
-	if (!kexec_load_permitted())
+	if (!kexec_load_permitted(flags & KEXEC_FILE_ON_CRASH))
 		return -EPERM;
 
 	/* Make sure we have a legal set of flags */
@@ -342,11 +344,12 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
 	if (!kexec_trylock())
 		return -EBUSY;
 
-	dest_image = &kexec_image;
-	if (flags & KEXEC_FILE_ON_CRASH) {
+	if (image_type == KEXEC_TYPE_CRASH) {
 		dest_image = &kexec_crash_image;
 		if (kexec_crash_image)
 			arch_kexec_unprotect_crashkres();
+	} else {
+		dest_image = &kexec_image;
 	}
 
 	if (flags & KEXEC_FILE_UNLOAD)

-- 
2.39.0.314.g84b9a713c41-goog-b4-0.11.0-dev-696ae

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Re: [PATCH v4 3/3] kexec: Introduce sysctl parameters kexec_load_limit_*

[Steven Rostedt]

On Wed, 21 Dec 2022 13:50:03 +0100
Ricardo Ribalda <ribalda@chromium.org> wrote:

> @@ -941,6 +995,20 @@ static struct ctl_table kexec_core_sysctls[] = {
>  		.extra1		= SYSCTL_ONE,
>  		.extra2		= SYSCTL_ONE,
>  	},
> +	{
> +		.procname	= "kexec_load_limit_panic",
> +		.data		= &load_limit_panic,
> +		.maxlen		= sizeof(load_limit_panic),

If I understand the sysctl logic correctly, the .maxlen is the maxlen of
the input to the sysctl, and not the data. Usually set to sizeof(data)
because most proc_handlers write to data directly.

In this case, I believe it's not even used (you override it with the
struct ctl_table tmp). I guess it doesn't really matter what it's set to.
Perhaps just set it to zero and leave it out?

> +		.mode		= 0644,
> +		.proc_handler	= kexec_limit_handler,
> +	},
> +	{
> +		.procname	= "kexec_load_limit_reboot",
> +		.data		= &load_limit_reboot,
> +		.maxlen		= sizeof(load_limit_reboot),

Same here.

-- Steve

> +		.mode		= 0644,
> +		.proc_handler	= kexec_limit_handler,
> +	},
>  	{ }
>  };
>  

Re: [PATCH v4 3/3] kexec: Introduce sysctl parameters kexec_load_limit_*

[Steven Rostedt]

On Wed, 21 Dec 2022 13:50:03 +0100
Ricardo Ribalda <ribalda@chromium.org> wrote:

> @@ -941,6 +995,20 @@ static struct ctl_table kexec_core_sysctls[] = {
>  		.extra1		= SYSCTL_ONE,
>  		.extra2		= SYSCTL_ONE,
>  	},
> +	{
> +		.procname	= "kexec_load_limit_panic",
> +		.data		= &load_limit_panic,
> +		.maxlen		= sizeof(load_limit_panic),

If I understand the sysctl logic correctly, the .maxlen is the maxlen of
the input to the sysctl, and not the data. Usually set to sizeof(data)
because most proc_handlers write to data directly.

In this case, I believe it's not even used (you override it with the
struct ctl_table tmp). I guess it doesn't really matter what it's set to.
Perhaps just set it to zero and leave it out?

> +		.mode		= 0644,
> +		.proc_handler	= kexec_limit_handler,
> +	},
> +	{
> +		.procname	= "kexec_load_limit_reboot",
> +		.data		= &load_limit_reboot,
> +		.maxlen		= sizeof(load_limit_reboot),

Same here.

-- Steve

> +		.mode		= 0644,
> +		.proc_handler	= kexec_limit_handler,
> +	},
>  	{ }
>  };
>  

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