[PATCH 4.10 23/48] powerpc/booke: Fix boot crash due to null hugepd

Greg Kroah-Hartman
2017-03-16T14:36:42Z

From: Laurentiu Tudor <laurentiu.tudor@nxp.com>

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.

Fixes: 20717e1ff526 ("powerpc/mm: Fix little-endian 4K hugetlb")
Reported-by: Madalin-Cristian Bucur <madalin.bucur@nxp.com>
Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
[mpe: Flesh out change log details.]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/arch/powerpc/include/asm/nohash/pgtable.h
+++ b/arch/powerpc/include/asm/nohash/pgtable.h
@@ -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
}