Patch "powerpc/booke: Fix boot crash due to null hugepd" has been added to the 4.10-stable tree

This is a note to let you know that I've just added the patch titled

powerpc/booke: Fix boot crash due to null hugepd

to the 4.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
powerpc-booke-fix-boot-crash-due-to-null-hugepd.patch
and it can be found in the queue-4.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Laurentiu Tudor <[email protected]>
Date: Thu, 16 Feb 2017 09:11:29 -0600
Subject: powerpc/booke: Fix boot crash due to null hugepd

From: Laurentiu Tudor <[email protected]>

commit 3fb66a70a4ae886445743354e4b60e54058bb3ff upstream.

On 32-bit book-e machines, hugepd_ok() no longer takes into account null hugepd values, causing this crash at boot:

  Unable to handle kernel paging request for data at address 0x80000000
  ...
  NIP [c0018378] follow_huge_addr+0x38/0xf0
  LR [c001836c] follow_huge_addr+0x2c/0xf0
  Call Trace:
   follow_huge_addr+0x2c/0xf0 (unreliable)
   follow_page_mask+0x40/0x3e0
   __get_user_pages+0xc8/0x450
   get_user_pages_remote+0x8c/0x250
   copy_strings+0x110/0x390
   copy_strings_kernel+0x2c/0x50
   do_execveat_common+0x478/0x630
   do_execve+0x2c/0x40
   try_to_run_init_process+0x18/0x60
   kernel_init+0xbc/0x110
   ret_from_kernel_thread+0x5c/0x64

This impacts all nxp (ex-freescale) 32-bit booke platforms.

This was caused by the change of hugepd_t.pd from signed to unsigned, and the update to the nohash version of hugepd_ok(). Previously hugepd_ok() could exclude all non-huge and NULL pgds using > 0, whereas now we need to explicitly check that the value is not zero and also that PD_HUGE is *clear*.

This isn't protected by the pgd_none() check in __find_linux_pte_or_hugepte() because on 32-bit we use pgtable-nopud.h, which causes the pgd_none() check to be always false.

---
 arch/powerpc/include/asm/nohash/pgtable.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -230,7 +230,7 @@ static inline int hugepd_ok(hugepd_t hpd
 	return ((hpd_val(hpd) & 0x4) != 0);
 #else
 	/* We clear the top bit to indicate hugepd */
-	return ((hpd_val(hpd) & PD_HUGE) ==  0);
+	return (hpd_val(hpd) && (hpd_val(hpd) & PD_HUGE) == 0);
 #endif
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.10/powerpc-booke-fix-boot-crash-due-to-null-hugepd.patch