PPC64 uses MMU features to enable/disable KUAP at boot time.
But feature fixups are applied way too early on PPC32.
But since commit c16728835eec ("powerpc/32: Manage KUAP in C"),
all KUAP is in C so it is now possible to use static branches.
Signed-off-by: Christophe Leroy <redacted>
---
arch/powerpc/include/asm/nohash/32/kup-8xx.h | 41 ++++++++++++++++++--
arch/powerpc/mm/nohash/8xx.c | 10 +++--
2 files changed, 45 insertions(+), 6 deletions(-)
diff --git a/arch/powerpc/include/asm/nohash/32/kup-8xx.h b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
index 295ef5639609..04ed17db6d3c 100644
--- a/arch/powerpc/include/asm/nohash/32/kup-8xx.h
+++ b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
@@ -11,8 +11,18 @@
#include <asm/reg.h>
+extern struct static_key_false disable_kuap_key;
+
+static __always_inline bool kuap_is_disabled(void)
+{
+ return static_branch_unlikely(&disable_kuap_key);
+}
+
static inline void kuap_save_and_lock(struct pt_regs *regs)
{
+ if (kuap_is_disabled())
+ return;
+
regs->kuap = mfspr(SPRN_MD_AP);
mtspr(SPRN_MD_AP, MD_APG_KUAP);
}@@ -23,12 +33,20 @@ static inline void kuap_user_restore(struct pt_regs *regs)
static inline void kuap_kernel_restore(struct pt_regs *regs, unsigned long kuap)
{
+ if (kuap_is_disabled())
+ return;
+
mtspr(SPRN_MD_AP, regs->kuap);
}
static inline unsigned long kuap_get_and_assert_locked(void)
{
- unsigned long kuap = mfspr(SPRN_MD_AP);
+ unsigned long kuap;
+
+ if (kuap_is_disabled())
+ return MD_APG_INIT;
+
+ kuap = mfspr(SPRN_MD_AP);
if (IS_ENABLED(CONFIG_PPC_KUAP_DEBUG))
WARN_ON_ONCE(kuap >> 16 != MD_APG_KUAP >> 16);@@ -38,25 +56,36 @@ static inline unsigned long kuap_get_and_assert_locked(void)
static inline void kuap_assert_locked(void)
{
- if (IS_ENABLED(CONFIG_PPC_KUAP_DEBUG))
+ if (IS_ENABLED(CONFIG_PPC_KUAP_DEBUG) && !kuap_is_disabled())
kuap_get_and_assert_locked();
}
static inline void allow_user_access(void __user *to, const void __user *from,
unsigned long size, unsigned long dir)
{
+ if (kuap_is_disabled())
+ return;
+
mtspr(SPRN_MD_AP, MD_APG_INIT);
}
static inline void prevent_user_access(void __user *to, const void __user *from,
unsigned long size, unsigned long dir)
{
+ if (kuap_is_disabled())
+ return;
+
mtspr(SPRN_MD_AP, MD_APG_KUAP);
}
static inline unsigned long prevent_user_access_return(void)
{
- unsigned long flags = mfspr(SPRN_MD_AP);
+ unsigned long flags;
+
+ if (kuap_is_disabled())
+ return MD_APG_INIT;
+
+ flags = mfspr(SPRN_MD_AP);
mtspr(SPRN_MD_AP, MD_APG_KUAP);
@@ -65,12 +94,18 @@ static inline unsigned long prevent_user_access_return(void)
static inline void restore_user_access(unsigned long flags)
{
+ if (kuap_is_disabled())
+ return;
+
mtspr(SPRN_MD_AP, flags);
}
static inline bool
bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
{
+ if (kuap_is_disabled())
+ return false;
+
return !((regs->kuap ^ MD_APG_KUAP) & 0xff000000);
}
diff --git a/arch/powerpc/mm/nohash/8xx.c b/arch/powerpc/mm/nohash/8xx.c
index 71bfdbedacee..a8d44e9342f3 100644
--- a/arch/powerpc/mm/nohash/8xx.c
+++ b/arch/powerpc/mm/nohash/8xx.c
@@ -256,12 +256,16 @@ void __init setup_kuep(bool disabled)
#endif
#ifdef CONFIG_PPC_KUAP
+struct static_key_false disable_kuap_key;
+
void __init setup_kuap(bool disabled)
{
- pr_info("Activating Kernel Userspace Access Protection\n");
+ if (disabled) {
+ static_branch_enable(&disable_kuap_key);
+ return;
+ }
- if (disabled)
- pr_warn("KUAP cannot be disabled yet on 8xx when compiled in\n");
+ pr_info("Activating Kernel Userspace Access Protection\n");
mtspr(SPRN_MD_AP, MD_APG_KUAP);
}--
2.25.0
Hi Christophe,
I love your patch! Yet something to improve:
[auto build test ERROR on powerpc/next]
[also build test ERROR on v5.13-rc4 next-20210603]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]
url: https://github.com/0day-ci/linux/commits/Christophe-Leroy/powerpc-8xx-Allow-disabling-KUAP-at-boot-time/20210603-170313
base: https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git next
config: powerpc-tqm8xx_defconfig (attached as .config)
compiler: powerpc-linux-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# https://github.com/0day-ci/linux/commit/95e4b5f2179c23e263e6889852978227583762f5
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Christophe-Leroy/powerpc-8xx-Allow-disabling-KUAP-at-boot-time/20210603-170313
git checkout 95e4b5f2179c23e263e6889852978227583762f5
# save the attached .config to linux build tree
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=powerpc
If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <redacted>
All errors (new ones prefixed by >>):
In file included from arch/powerpc/include/asm/kup.h:22,
from arch/powerpc/include/asm/uaccess.h:9,
from include/linux/uaccess.h:11,
from include/linux/sched/task.h:11,
from include/linux/sched/signal.h:9,
from include/linux/rcuwait.h:6,
from include/linux/percpu-rwsem.h:7,
from include/linux/fs.h:33,
from include/linux/compat.h:17,
from arch/powerpc/kernel/asm-offsets.c:14:
arch/powerpc/include/asm/nohash/32/kup-8xx.h: In function 'kuap_is_disabled':quoted
arch/powerpc/include/asm/nohash/32/kup-8xx.h:18:9: error: implicit declaration of function 'static_branch_unlikely' [-Werror=implicit-function-declaration]
18 | return static_branch_unlikely(&disable_kuap_key);
| ^~~~~~~~~~~~~~~~~~~~~~
cc1: some warnings being treated as errors
--
In file included from arch/powerpc/include/asm/kup.h:22,
from arch/powerpc/include/asm/uaccess.h:9,
from include/linux/uaccess.h:11,
from include/linux/sched/task.h:11,
from include/linux/sched/signal.h:9,
from include/linux/rcuwait.h:6,
from include/linux/percpu-rwsem.h:7,
from include/linux/fs.h:33,
from include/linux/compat.h:17,
from arch/powerpc/kernel/asm-offsets.c:14:
arch/powerpc/include/asm/nohash/32/kup-8xx.h: In function 'kuap_is_disabled':quoted
arch/powerpc/include/asm/nohash/32/kup-8xx.h:18:9: error: implicit declaration of function 'static_branch_unlikely' [-Werror=implicit-function-declaration]
18 | return static_branch_unlikely(&disable_kuap_key);
| ^~~~~~~~~~~~~~~~~~~~~~
cc1: some warnings being treated as errors
make[2]: *** [scripts/Makefile.build:117: arch/powerpc/kernel/asm-offsets.s] Error 1
make[2]: Target '__build' not remade because of errors.
make[1]: *** [Makefile:1227: prepare0] Error 2
make[1]: Target 'modules_prepare' not remade because of errors.
make: *** [Makefile:215: __sub-make] Error 2
make: Target 'modules_prepare' not remade because of errors.
--
In file included from arch/powerpc/include/asm/kup.h:22,
from arch/powerpc/include/asm/uaccess.h:9,
from include/linux/uaccess.h:11,
from include/linux/sched/task.h:11,
from include/linux/sched/signal.h:9,
from include/linux/rcuwait.h:6,
from include/linux/percpu-rwsem.h:7,
from include/linux/fs.h:33,
from include/linux/compat.h:17,
from arch/powerpc/kernel/asm-offsets.c:14:
arch/powerpc/include/asm/nohash/32/kup-8xx.h: In function 'kuap_is_disabled':quoted
arch/powerpc/include/asm/nohash/32/kup-8xx.h:18:9: error: implicit declaration of function 'static_branch_unlikely' [-Werror=implicit-function-declaration]
18 | return static_branch_unlikely(&disable_kuap_key);
| ^~~~~~~~~~~~~~~~~~~~~~
cc1: some warnings being treated as errors
make[2]: *** [scripts/Makefile.build:117: arch/powerpc/kernel/asm-offsets.s] Error 1
make[2]: Target '__build' not remade because of errors.
make[1]: *** [Makefile:1227: prepare0] Error 2
make[1]: Target 'prepare' not remade because of errors.
make: *** [Makefile:215: __sub-make] Error 2
make: Target 'prepare' not remade because of errors.
vim +/static_branch_unlikely +18 arch/powerpc/include/asm/nohash/32/kup-8xx.h
15
16 static __always_inline bool kuap_is_disabled(void)
17 {
> 18 return static_branch_unlikely(&disable_kuap_key);
19 }
20
---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org