It is possible to disable KUAP at boottime with 'nosmap' parameter.
That is implemented with jump_label hence adds a 'nop' in front
of each open/close of userspace access.
>From a security point of view it makes sence to disallow disabling
KUAP. And on processors like the 8xx where 'nop' is not seamless,
it saves a few cycles.
In addition, objtool UACCESS validation cannot cope with that
feature because it visits every static branches independentely and
is not able to see that when a UACCESS enable is skipped, the
matching UACCESS disable is skipped as well.
So make KUAP always active when selected in kernel config.
In the future it may be re-implemented by noping the instructions
instead of using static branches.
Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu>
---
arch/powerpc/include/asm/kup.h | 4 +---
arch/powerpc/mm/book3s32/kuap.c | 15 ++++++---------
arch/powerpc/mm/init-common.c | 6 +++---
arch/powerpc/mm/nohash/kup.c | 8 +-------
4 files changed, 11 insertions(+), 22 deletions(-)
diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
index 74b7f4cee2ed..a02340535efa 100644
--- a/arch/powerpc/include/asm/kup.h
+++ b/arch/powerpc/include/asm/kup.h
@@ -49,11 +49,9 @@ void setup_kuep(bool disabled);
void setup_kuap(bool disabled);
#ifndef kuap_is_disabled
-extern struct static_key_false disable_kuap_key;
-
static __always_inline bool kuap_is_disabled(void)
{
- return static_branch_unlikely(&disable_kuap_key);
+ return false;
}
#endif
#else
diff --git a/arch/powerpc/mm/book3s32/kuap.c b/arch/powerpc/mm/book3s32/kuap.c
index c5484729b595..639219d0a821 100644
--- a/arch/powerpc/mm/book3s32/kuap.c
+++ b/arch/powerpc/mm/book3s32/kuap.c
@@ -17,17 +17,14 @@ EXPORT_SYMBOL(kuap_unlock_all_ool);
void setup_kuap(bool disabled)
{
- if (!disabled) {
- kuap_lock_all_ool();
- init_mm.context.sr0 |= SR_KS;
- current->thread.sr0 |= SR_KS;
- }
+ WARN_ON(disabled);
+
+ kuap_lock_all_ool();
+ init_mm.context.sr0 |= SR_KS;
+ current->thread.sr0 |= SR_KS;
if (smp_processor_id() != boot_cpuid)
return;
- if (disabled)
- static_branch_enable(&disable_kuap_key);
- else
- pr_info("Activating Kernel Userspace Access Protection\n");
+ pr_info("Activating Kernel Userspace Access Protection\n");
}
diff --git a/arch/powerpc/mm/init-common.c b/arch/powerpc/mm/init-common.c
index 74e140b1efef..237086742ec7 100644
--- a/arch/powerpc/mm/init-common.c
+++ b/arch/powerpc/mm/init-common.c
@@ -32,9 +32,6 @@ EXPORT_SYMBOL_GPL(kernstart_virt_addr);
bool disable_kuep = !IS_ENABLED(CONFIG_PPC_KUEP);
bool disable_kuap = !IS_ENABLED(CONFIG_PPC_KUAP);
-struct static_key_false disable_kuap_key;
-EXPORT_SYMBOL(disable_kuap_key);
-
static int __init parse_nosmep(char *p)
{
if (!IS_ENABLED(CONFIG_PPC_BOOK3S_64))
@@ -48,6 +45,9 @@ early_param("nosmep", parse_nosmep);
static int __init parse_nosmap(char *p)
{
+ if (!IS_ENABLED(CONFIG_PPC_BOOK3S_64))
+ return 0;
+
disable_kuap = true;
pr_warn("Disabling Kernel Userspace Access Protection\n");
return 0;
diff --git a/arch/powerpc/mm/nohash/kup.c b/arch/powerpc/mm/nohash/kup.c
index 4e22adfa2aa8..3bb79f89de06 100644
--- a/arch/powerpc/mm/nohash/kup.c
+++ b/arch/powerpc/mm/nohash/kup.c
@@ -15,13 +15,7 @@
#ifdef CONFIG_PPC_KUAP
void setup_kuap(bool disabled)
{
- if (disabled) {
- if (IS_ENABLED(CONFIG_40x))
- disable_kuep = true;
- if (smp_processor_id() == boot_cpuid)
- static_branch_enable(&disable_kuap_key);
- return;
- }
+ WARN_ON(disabled);
pr_info("Activating Kernel Userspace Access Protection\n");
--
2.40.1
