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 <[email protected]>
To: Eric Biederman <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: Joel Fernandes (Google) <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Ross Zwisler <[email protected]>
To: Philipp Rudo <[email protected]>
To: Guilherme G. Piccoli <[email protected]>
Signed-off-by: Ricardo Ribalda <[email protected]>
---
Changes in v3:
- s/paramter/parameter/ Thanks Ghilherme!
- s/permited/permitted/ Thanks Joel!
- Link to v2: https://lore.kernel.org/r/[email protected]
Changes in v2:
- Instead of kexec_reboot_disabled, add two new counters (Thanks Philipp!)
- Link to v1: https://lore.kernel.org/r/[email protected]
---
Ricardo Ribalda (3):
Documentation: sysctl: Correct kexec_load_disabled
kexec: Factor out kexec_load_permitted
kexec: Introduce parameters load_limit_reboot and load_limit_panic
Documentation/admin-guide/kernel-parameters.txt | 14 ++++
Documentation/admin-guide/sysctl/kernel.rst | 7 +-
include/linux/kexec.h | 3 +-
kernel/kexec.c | 2 +-
kernel/kexec_core.c | 98 ++++++++++++++++++++++++-
kernel/kexec_file.c | 2 +-
6 files changed, 119 insertions(+), 7 deletions(-)
---
base-commit: 479174d402bcf60789106eedc4def3957c060bad
change-id: 20221114-disable-kexec-reset-19b7e117338f
Best regards,
--
Ricardo Ribalda <[email protected]>
kexec_load_disabled affects both ``kexec_load`` and ``kexec_file_load``
syscalls. Make it explicit.
Signed-off-by: Ricardo Ribalda <[email protected]>
---
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
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 <[email protected]>
---
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
On Tue, 20 Dec 2022 23:05:45 +0100
Ricardo Ribalda <[email protected]> wrote:
I hate to be the grammar police, but..
> Add two parameter to specify how many times a kexec kernel can be loaded.
"parameters"
>
> 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 <[email protected]>
> ---
> 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).
Perhaps state:
smaller positive value than the current one or if
current is currently -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))
Note, here we have KEXEC_ON_CRASH (see bottom).
> 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 = {
Perhaps make the above static?
> + .mutex = __MUTEX_INITIALIZER(load_limit_reboot.mutex),
> + .limit = -1,
> +};
> +
> +struct kexec_load_limit load_limit_panic = {
static?
> + .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;
Looks better if "int ret;" is after the "limit".
> +
> + mutex_lock(&limit->mutex);
> + ret = scnprintf(buffer, PAGE_SIZE, "%i\n", limit->limit);
The above string can be at most "-2147483648\n\0"
Which is 13 characters. Why use PAGE_SIZE. Or scnprintf(), and not just
state:
/* buffer is PAGE_SIZE, much larger than what %i can be */
ret = sprintf(buffer, "%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);
I wonder if anything less than -1 should be invalid.
> +
> + mutex_lock(&limit->mutex);
> +
> + if (new_val == -1 && limit->limit != -1) {
If -1 can't change the value, why allow it to be passed in to begin with.
Perhaps we should only allow sysctl to set positive values? Would make the
code simpler.
> + ret = -EINVAL;
> + goto done;
> + }
> +
> + if (limit->limit != -1 && new_val > limit->limit) {
Since the above documentation said "small than" perhaps ">="?
> + 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");
Wait, why the module params if this can not be a module?
The kernel/kexec.c is decided via CONFIG_KEXEC_CORE which is bool. Either
builtin or not at all. No module selection possible.
For kernel parameters, we should just use __setup(), right?
> +
> +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))
Here we have KEXEC_FILE_FLAGS, where above it was KEXCE_FILE_CRASH.
This is confusing to what denotes the "crash_image" boolean. Can we just
pass in flags and figure it out in the kexec_load_permitted() function?
-- Steve
> return -EPERM;
>
> /* Make sure we have a legal set of flags */
>
Hi Steven
Thanks for your review!!! Will send a new version.
After giving it a thought... you are right :). setting the current
value should return -EINVAL. We should only return OK if we actually
do something.
On Wed, 21 Dec 2022 at 01:22, Steven Rostedt <[email protected]> wrote:
>
> On Tue, 20 Dec 2022 23:05:45 +0100
> Ricardo Ribalda <[email protected]> wrote:
>
> I hate to be the grammar police, but..
>
> > Add two parameter to specify how many times a kexec kernel can be loaded.
>
> "parameters"
>
> >
> > 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 <[email protected]>
> > ---
> > 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).
>
> Perhaps state:
> smaller positive value than the current one or if
> current is currently -1.
I find it a bit complicated..
What about:
During runtime this parameter can be modified with a more restrictive value
>
> > +
> > + 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))
>
> Note, here we have KEXEC_ON_CRASH (see bottom).
>
> > 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 = {
>
> Perhaps make the above static?
>
> > + .mutex = __MUTEX_INITIALIZER(load_limit_reboot.mutex),
> > + .limit = -1,
> > +};
> > +
> > +struct kexec_load_limit load_limit_panic = {
>
> static?
>
> > + .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;
>
> Looks better if "int ret;" is after the "limit".
>
> > +
> > + mutex_lock(&limit->mutex);
> > + ret = scnprintf(buffer, PAGE_SIZE, "%i\n", limit->limit);
>
> The above string can be at most "-2147483648\n\0"
>
> Which is 13 characters. Why use PAGE_SIZE. Or scnprintf(), and not just
> state:
>
like it!
> /* buffer is PAGE_SIZE, much larger than what %i can be */
> ret = sprintf(buffer, "%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);
>
> I wonder if anything less than -1 should be invalid.
>
> > +
> > + mutex_lock(&limit->mutex);
> > +
> > + if (new_val == -1 && limit->limit != -1) {
>
> If -1 can't change the value, why allow it to be passed in to begin with.
>
> Perhaps we should only allow sysctl to set positive values? Would make the
> code simpler.
>
> > + ret = -EINVAL;
> > + goto done;
> > + }
> > +
> > + if (limit->limit != -1 && new_val > limit->limit) {
>
> Since the above documentation said "small than" perhaps ">="?
>
> > + 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");
>
> Wait, why the module params if this can not be a module?
>
> The kernel/kexec.c is decided via CONFIG_KEXEC_CORE which is bool. Either
> builtin or not at all. No module selection possible.
>
> For kernel parameters, we should just use __setup(), right?
Isn't __setup() only kernel parameter and then it cannot be updated on runtime?
What about using late_param_cb? and remove MODULE_PARAM_DESC ?
I think this is how these parameters work
$ ls /sys/module/kernel/parameters/
consoleblank crash_kexec_post_notifiers ignore_rlimit_data
initcall_debug module_blacklist panic panic_on_warn panic_print
pause_on_oops
>
> > +
> > +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))
>
> Here we have KEXEC_FILE_FLAGS, where above it was KEXCE_FILE_CRASH.
>
> This is confusing to what denotes the "crash_image" boolean. Can we just
> pass in flags and figure it out in the kexec_load_permitted() function?
This is a typo and a bad one!, thanks for catching up!.
It should be KEXEC_ON_CRASH and KEXEC_FILE_ON_CRASH, Of course both
have different values
I could pass the flags and then check for flags & (KEXEC_ON_CRASH |
KEXEC_FILE_ON_CRASH)... but not sure if it is better
>
> -- Steve
>
>
> > return -EPERM;
> >
> > /* Make sure we have a legal set of flags */
> >
>
--
Ricardo Ribalda
On Wed, 21 Dec 2022 02:22:57 +0100
Ricardo Ribalda <[email protected]> wrote:
> > > + 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).
> >
> > Perhaps state:
> > smaller positive value than the current one or if
> > current is currently -1.
>
> I find it a bit complicated..
> What about:
>
> During runtime this parameter can be modified with a more restrictive value
Sure. That's better than the original.
> > > +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");
> >
> > Wait, why the module params if this can not be a module?
> >
> > The kernel/kexec.c is decided via CONFIG_KEXEC_CORE which is bool. Either
> > builtin or not at all. No module selection possible.
> >
> > For kernel parameters, we should just use __setup(), right?
>
> Isn't __setup() only kernel parameter and then it cannot be updated on runtime?
Yes, but then we use sysctl.
>
> What about using late_param_cb? and remove MODULE_PARAM_DESC ?
>
> I think this is how these parameters work
>
> $ ls /sys/module/kernel/parameters/
> consoleblank crash_kexec_post_notifiers ignore_rlimit_data
> initcall_debug module_blacklist panic panic_on_warn panic_print
> pause_on_oops
Well, I think those are more leftovers and not something we want to add to.
I believe sysctl is the better option, and a more common one:
$ ls /proc/sys/kernel/
acct perf_event_max_contexts_per_stack
acpi_video_flags perf_event_max_sample_rate
auto_msgmni perf_event_max_stack
bootloader_type perf_event_mlock_kb
bootloader_version perf_event_paranoid
bpf_stats_enabled pid_max
cad_pid poweroff_cmd
cap_last_cap print-fatal-signals
core_pattern printk
core_pipe_limit printk_delay
core_uses_pid printk_devkmsg
ctrl-alt-del printk_ratelimit
dmesg_restrict printk_ratelimit_burst
domainname pty
firmware_config random
ftrace_dump_on_oops randomize_va_space
ftrace_enabled real-root-dev
hardlockup_all_cpu_backtrace sched_autogroup_enabled
hardlockup_panic sched_child_runs_first
hostname sched_deadline_period_max_us
hotplug sched_deadline_period_min_us
hung_task_all_cpu_backtrace sched_energy_aware
hung_task_check_count sched_rr_timeslice_ms
hung_task_check_interval_secs sched_rt_period_us
hung_task_panic sched_rt_runtime_us
hung_task_timeout_secs sched_util_clamp_max
hung_task_warnings sched_util_clamp_min
io_delay_type sched_util_clamp_min_rt_default
kexec_load_disabled seccomp
keys sem
kptr_restrict sem_next_id
max_lock_depth shmall
max_rcu_stall_to_panic shmmax
modprobe shmmni
modules_disabled shm_next_id
msgmax shm_rmid_forced
msgmnb softlockup_all_cpu_backtrace
msgmni softlockup_panic
msg_next_id soft_watchdog
ngroups_max stack_tracer_enabled
nmi_watchdog sysctl_writes_strict
ns_last_pid sysrq
numa_balancing tainted
oops_all_cpu_backtrace task_delayacct
osrelease threads-max
ostype timer_migration
overflowgid traceoff_on_warning
overflowuid tracepoint_printk
panic unknown_nmi_panic
panic_on_io_nmi unprivileged_bpf_disabled
panic_on_oops usermodehelper
panic_on_rcu_stall version
panic_on_unrecovered_nmi watchdog
panic_on_warn watchdog_cpumask
panic_print watchdog_thresh
perf_cpu_time_max_percent yama
> I could pass the flags and then check for flags & (KEXEC_ON_CRASH |
> KEXEC_FILE_ON_CRASH)... but not sure if it is better
It keeps the processing in a single place, which helps avoid bugs like this.
-- Steve