[PATCH -next] powerpc/mm/ptdump: fix an undefined behaviour

[Qian Cai]

Booting a power9 server with hash MMU could trigger an undefined
behaviour because pud_offset(p4d, 0) will do,

0 >> (PAGE_SHIFT:16 + PTE_INDEX_SIZE:8 + H_PMD_INDEX_SIZE:10)

 UBSAN: shift-out-of-bounds in arch/powerpc/mm/ptdump/ptdump.c:282:15
 shift exponent 34 is too large for 32-bit type 'int'
 CPU: 6 PID: 1 Comm: swapper/0 Not tainted 5.6.0-rc4-next-20200303+ #13
 Call Trace:
 dump_stack+0xf4/0x164 (unreliable)
 ubsan_epilogue+0x18/0x78
 __ubsan_handle_shift_out_of_bounds+0x160/0x21c
 walk_pagetables+0x2cc/0x700
 walk_pud at arch/powerpc/mm/ptdump/ptdump.c:282
 (inlined by) walk_pagetables at arch/powerpc/mm/ptdump/ptdump.c:311
 ptdump_check_wx+0x8c/0xf0
 mark_rodata_ro+0x48/0x80
 kernel_init+0x74/0x194
 ret_from_kernel_thread+0x5c/0x74

Fixes: 8eb07b187000 ("powerpc/mm: Dump linux pagetables")
Signed-off-by: Qian Cai <cai at lca.pw>
---

Notes for maintainers:

This is on the top of the linux-next commit "powerpc: add support for
folded p4d page tables" which is in the Andrew's tree.

 arch/powerpc/mm/ptdump/ptdump.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/ptdump/ptdump.c b/arch/powerpc/mm/ptdump/ptdump.c
index 9d6256b61df3..b530f81398a7 100644
--- a/arch/powerpc/mm/ptdump/ptdump.c
+++ b/arch/powerpc/mm/ptdump/ptdump.c
@@ -279,7 +279,7 @@ static void walk_pmd(struct pg_state *st, pud_t *pud, unsigned long start)
 
 static void walk_pud(struct pg_state *st, p4d_t *p4d, unsigned long start)
 {
-	pud_t *pud = pud_offset(p4d, 0);
+	pud_t *pud = pud_offset(p4d, 0UL);
 	unsigned long addr;
 	unsigned int i;
 
-- 
2.21.0 (Apple Git-122.2)