Re: [PATCH v5 8/8] lkdtm/powerpc: Fix code patching hijack test

On Thu Aug 5, 2021 at 4:18 AM CDT, Christophe Leroy wrote:

Le 13/07/2021 à 07:31, Christopher M. Riedl a écrit :

quoted

Code patching on powerpc with a STRICT_KERNEL_RWX uses a userspace
address in a temporary mm on Radix now. Use __put_user() to avoid write
failures due to KUAP when attempting a "hijack" on the patching address.
__put_user() also works with the non-userspace, vmalloc-based patching
address on non-Radix MMUs.

It is not really clean to use __put_user() on non user address,
allthought it works by change.

I think it would be better to do something like

if (is_kernel_addr(addr))
copy_to_kernel_nofault(...);
else
copy_to_user_nofault(...);

Yes that looks much better. I'll pick this up and try it for the next
spin. Thanks!

quoted

Signed-off-by: Christopher M. Riedl <redacted>
---
  drivers/misc/lkdtm/perms.c | 9 ---------
  1 file changed, 9 deletions(-)

diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
index 41e87e5f9cc86..da6a34a0a49fb 100644
--- a/drivers/misc/lkdtm/perms.c
+++ b/drivers/misc/lkdtm/perms.c

@@ -262,16 +262,7 @@ static inline u32 lkdtm_read_patch_site(void)
  /* Returns True if the write succeeds */
  static inline bool lkdtm_try_write(u32 data, u32 *addr)
  {
-#ifdef CONFIG_PPC
-	__put_kernel_nofault(addr, &data, u32, err);
-	return true;
-
-err:
-	return false;
-#endif
-#ifdef CONFIG_X86_64
  	return !__put_user(data, addr);
-#endif
  }
  
  static int lkdtm_patching_cpu(void *data)