The amount of code executed with enabled user space access (unlocked KUAP)
should be minimal. However with CONFIG_PROVE_LOCKING or
CONFIG_DEBUG_ATOMIC_SLEEP enabled, might_fault() may end up replaying
interrupts which in turn may access the user space and forget to restore
the KUAP state.
The problem places are strncpy_from_user (and similar) which unlock KUAP
and call unsafe_get_user -> __get_user_allowed -> __get_user_nocheck()
with do_allow=false to skip KUAP as the caller took care of it.
This changes __get_user_nocheck() to look at @do_allow to decide whether
to skip might_fault(). Since strncpy_from_user/etc call might_fault()
anyway before unlocking KUAP, there should be no visible change.
Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru>
---
This an attempt to fix that KUAP restore problem from
"powerpc/kuap: Restore AMR after replaying soft interrupts".
---
arch/powerpc/include/asm/uaccess.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/powerpc/include/asm/uaccess.h
b/arch/powerpc/include/asm/uaccess.h
index 501c9a79038c..cd6c0427a9e2 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -313,7 +313,7 @@ do {
\
__typeof__(size) __gu_size = (size); \
\
__chk_user_ptr(__gu_addr); \
- if (!is_kernel_addr((unsigned long)__gu_addr)) \
+ if (!do_allow && !is_kernel_addr((unsigned long)__gu_addr)) \
might_fault(); \
barrier_nospec(); \
if (do_allow)
\
--
2.17.1
