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 */ > _______________________________________________ kexec mailing list [email protected] http://lists.infradead.org/mailman/listinfo/kexec
