[PATCH 2/2] arm64: uaccess: disable preempt during uaccess PSTATE.{PAN, TCO}

[Pingfan Liu]

For the pair of
uaccess_enable_privileged()/uaccess_disable_privileged(), if preemption
happens, the exposure of the access to user space by another code piece
is unexpected.

For the pair of
__uaccess_enable_tco_async()/__uaccess_disable_tco_async(), the change
of PSTATE.TCO is exposed unexpectedly.

For the two cases, simply disable preemption to fix the issue.

Signed-off-by: Pingfan Liu <kernelfans at gmail.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will at kernel.org>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Vincenzo Frascino <vincenzo.frascino at arm.com>
Cc: Andrey Konovalov <andreyknvl at gmail.com>
Cc: Arnd Bergmann <arnd at arndb.de>
To: linux-arm-kernel at lists.infradead.org
---
 arch/arm64/include/asm/uaccess.h | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 406888877bbd..37d5531f210d 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -193,14 +193,18 @@ static inline void __uaccess_enable_tco(void)
  */
 static inline void __uaccess_disable_tco_async(void)
 {
-	if (system_uses_mte_async_or_asymm_mode())
-		 __uaccess_disable_tco();
+	if (system_uses_mte_async_or_asymm_mode()) {
+		__uaccess_disable_tco();
+		preempt_enable();
+	}
 }
 
 static inline void __uaccess_enable_tco_async(void)
 {
-	if (system_uses_mte_async_or_asymm_mode())
+	if (system_uses_mte_async_or_asymm_mode()) {
+		preempt_disable();
 		__uaccess_enable_tco();
+	}
 }
 
 static inline void uaccess_disable_privileged(void)
@@ -208,13 +212,16 @@ static inline void uaccess_disable_privileged(void)
 	__uaccess_disable_tco();
 
 	if (uaccess_ttbr0_disable())
-		return;
+		goto out;
 
 	__uaccess_enable_hw_pan();
+out:
+	preempt_enable();
 }
 
 static inline void uaccess_enable_privileged(void)
 {
+	preempt_disable();
 	__uaccess_enable_tco();
 
 	if (uaccess_ttbr0_enable())
-- 
2.31.1