| Message ID | 20250321102422.640271-2-nik.borisov@suse.com (mailing list archive) |
|---|---|
| State | Under Review |
| Delegated to: | Paul Moore |
| Headers | show |
| Series | Allow individual features to be locked down | expand |
On Fri, Mar 21, 2025 at 12:24:20PM +0200, Nikolay Borisov wrote: > Tracking the lockdown at the depth granularity rather than at the > individual is somewhat inflexible as it provides an "all or nothing" > approach. Instead there are use cases where it will be useful to be > able to lockdown individual features - TDX for example wants to disable > access to just /dev/mem. > > To accommodate this use case switch the internal implementation to using > a bitmap so that individual lockdown features can be turned on. At the > same time retain the existing semantic where > INTEGRITY_MAX/CONFIDENTIALITY_MAX are treated as wildcards meaning "lock > everything below me". > > Signed-off-by: Nikolay Borisov <nik.borisov@suse.com> Reviewed-by: Serge Hallyn <sergeh@kernel.org> but one comment below > --- > security/lockdown/lockdown.c | 19 ++++++++++++------- > 1 file changed, 12 insertions(+), 7 deletions(-) > > diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c > index cf83afa1d879..5014d18c423f 100644 > --- a/security/lockdown/lockdown.c > +++ b/security/lockdown/lockdown.c > @@ -10,12 +10,13 @@ > * 2 of the Licence, or (at your option) any later version. > */ > > +#include <linux/bitmap.h> > #include <linux/security.h> > #include <linux/export.h> > #include <linux/lsm_hooks.h> > #include <uapi/linux/lsm.h> > > -static enum lockdown_reason kernel_locked_down; > +static DECLARE_BITMAP(kernel_locked_down, LOCKDOWN_CONFIDENTIALITY_MAX); > > static const enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE, > LOCKDOWN_INTEGRITY_MAX, > @@ -26,10 +27,15 @@ static const enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE, > */ > static int lock_kernel_down(const char *where, enum lockdown_reason level) > { > - if (kernel_locked_down >= level) > - return -EPERM; > > - kernel_locked_down = level; > + if (level > LOCKDOWN_CONFIDENTIALITY_MAX) > + return -EINVAL; > + > + if (level == LOCKDOWN_INTEGRITY_MAX || level == LOCKDOWN_CONFIDENTIALITY_MAX) > + bitmap_set(kernel_locked_down, 1, level); > + else > + bitmap_set(kernel_locked_down, level, 1); > + > pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n", > where); > return 0; > @@ -62,13 +68,12 @@ static int lockdown_is_locked_down(enum lockdown_reason what) > "Invalid lockdown reason")) > return -EPERM; > > - if (kernel_locked_down >= what) { > + if (test_bit(what, kernel_locked_down)) { > if (lockdown_reasons[what]) > pr_notice_ratelimited("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n", > current->comm, lockdown_reasons[what]); > return -EPERM; > } > - > return 0; > } > > @@ -105,7 +110,7 @@ static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count, Context here is: static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos) { char temp[80] = ""; int i, offset = 0; for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) { enum lockdown_reason level = lockdown_levels[i]; ... > if (lockdown_reasons[level]) { > const char *label = lockdown_reasons[level]; > > - if (kernel_locked_down == level) > + if (test_bit(level, kernel_locked_down)) Right now this is still just looping over the lockdown_levels, and so it can't get longer than "none [integrity] [confidentiality]" which fits easily into the 80 chars of temp. But I'm worried that someone will change this loop i a way that violates that. Could you just switch this to a snprintf that checks its result for < 0 and >= n , or some other sanity check? > offset += sprintf(temp+offset, "[%s] ", label); > else > offset += sprintf(temp+offset, "%s ", label); > -- > 2.43.0 >
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c index cf83afa1d879..5014d18c423f 100644 --- a/security/lockdown/lockdown.c +++ b/security/lockdown/lockdown.c @@ -10,12 +10,13 @@ * 2 of the Licence, or (at your option) any later version. */ +#include <linux/bitmap.h> #include <linux/security.h> #include <linux/export.h> #include <linux/lsm_hooks.h> #include <uapi/linux/lsm.h> -static enum lockdown_reason kernel_locked_down; +static DECLARE_BITMAP(kernel_locked_down, LOCKDOWN_CONFIDENTIALITY_MAX); static const enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE, LOCKDOWN_INTEGRITY_MAX, @@ -26,10 +27,15 @@ static const enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE, */ static int lock_kernel_down(const char *where, enum lockdown_reason level) { - if (kernel_locked_down >= level) - return -EPERM; - kernel_locked_down = level; + if (level > LOCKDOWN_CONFIDENTIALITY_MAX) + return -EINVAL; + + if (level == LOCKDOWN_INTEGRITY_MAX || level == LOCKDOWN_CONFIDENTIALITY_MAX) + bitmap_set(kernel_locked_down, 1, level); + else + bitmap_set(kernel_locked_down, level, 1); + pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n", where); return 0; @@ -62,13 +68,12 @@ static int lockdown_is_locked_down(enum lockdown_reason what) "Invalid lockdown reason")) return -EPERM; - if (kernel_locked_down >= what) { + if (test_bit(what, kernel_locked_down)) { if (lockdown_reasons[what]) pr_notice_ratelimited("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n", current->comm, lockdown_reasons[what]); return -EPERM; } - return 0; } @@ -105,7 +110,7 @@ static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count, if (lockdown_reasons[level]) { const char *label = lockdown_reasons[level]; - if (kernel_locked_down == level) + if (test_bit(level, kernel_locked_down)) offset += sprintf(temp+offset, "[%s] ", label); else offset += sprintf(temp+offset, "%s ", label);
Tracking the lockdown at the depth granularity rather than at the individual is somewhat inflexible as it provides an "all or nothing" approach. Instead there are use cases where it will be useful to be able to lockdown individual features - TDX for example wants to disable access to just /dev/mem. To accommodate this use case switch the internal implementation to using a bitmap so that individual lockdown features can be turned on. At the same time retain the existing semantic where INTEGRITY_MAX/CONFIDENTIALITY_MAX are treated as wildcards meaning "lock everything below me". Signed-off-by: Nikolay Borisov <nik.borisov@suse.com> --- security/lockdown/lockdown.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-)