powerpc/kasan: Fix kasan_remap_early_shadow_ro()

[ Upstream commit af92bad ]

At the moment kasan_remap_early_shadow_ro() does nothing, because
k_end is 0 and k_cur < 0 is always true.

Change the test to k_cur != k_end, as done in
kasan_init_shadow_page_tables()

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Fixes: cbd1899 ("powerpc/mm: Fix an Oops in kasan_mmu_init()")
Cc: stable@vger.kernel.org
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/4e7b56865e01569058914c991143f5961b5d4719.1583507333.git.christophe.leroy@c-s.fr
Signed-off-by: Sasha Levin <sashal@kernel.org>

arch/powerpc/mm/kasan/kasan_init_32.c

@@ -101,7 +101,7 @@ static void __init kasan_remap_early_shadow_ro(void)
 
 	kasan_populate_pte(kasan_early_shadow_pte, prot);
 
-	for (k_cur = k_start & PAGE_MASK; k_cur < k_end; k_cur += PAGE_SIZE) {
+	for (k_cur = k_start & PAGE_MASK; k_cur != k_end; k_cur += PAGE_SIZE) {
 		pmd_t *pmd = pmd_offset(pud_offset(pgd_offset_k(k_cur), k_cur), k_cur);
 		pte_t *ptep = pte_offset_kernel(pmd, k_cur);