riscv: mm: add missing memcpy in kasan_init

Hi Atish,

It seems that the panic is due to the missing memcpy during kasan_init.
Could you please check whether this patch is helpful?

When doing kasan_populate, the new allocated base_pud/base_p4d should
contain kasan_early_shadow_{pud, p4d}'s content. Add the missing memcpy
to avoid page fault when read/write kasan shadow region.

Tested on:
 - qemu with sv57 and CONFIG_KASAN on.
 - qemu with sv48 and CONFIG_KASAN on.
Signed-off-by: Qinglin Pan <panqinglin2020@iscas.ac.cn>
Tested-by: Atish Patra <atishp@rivosinc.com>
Fixes: 8fbdccd2 ("riscv: mm: Support kasan for sv57")
Link: https://lore.kernel.org/r/20221009083050.3814850-1-panqinglin2020@iscas.ac.cnSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/mm/kasan_init.c

@@ -113,6 +113,8 @@ static void __init kasan_populate_pud(pgd_t *pgd,
 		base_pud = pt_ops.get_pud_virt(pfn_to_phys(_pgd_pfn(*pgd)));
 	} else if (pgd_none(*pgd)) {
 		base_pud = memblock_alloc(PTRS_PER_PUD * sizeof(pud_t), PAGE_SIZE);
+		memcpy(base_pud, (void *)kasan_early_shadow_pud,
+			sizeof(pud_t) * PTRS_PER_PUD);
 	} else {
 		base_pud = (pud_t *)pgd_page_vaddr(*pgd);
 		if (base_pud == lm_alias(kasan_early_shadow_pud)) {
@@ -173,8 +175,11 @@ static void __init kasan_populate_p4d(pgd_t *pgd,
 		base_p4d = pt_ops.get_p4d_virt(pfn_to_phys(_pgd_pfn(*pgd)));
 	} else {
 		base_p4d = (p4d_t *)pgd_page_vaddr(*pgd);
-		if (base_p4d == lm_alias(kasan_early_shadow_p4d))
+		if (base_p4d == lm_alias(kasan_early_shadow_p4d)) {
 			base_p4d = memblock_alloc(PTRS_PER_PUD * sizeof(p4d_t), PAGE_SIZE);
+			memcpy(base_p4d, (void *)kasan_early_shadow_p4d,
+				sizeof(p4d_t) * PTRS_PER_P4D);
+		}
 	}
 
 	p4dp = base_p4d + p4d_index(vaddr);