[v6 11/15] arm64/kasan: explicitly zero kasan shadow memory

Pavel Tatashin
2017-08-07T20:43:50Z

To optimize the performance of struct page initialization,
vmemmap_populate() will no longer zero memory.

We must explicitly zero the memory that is allocated by vmemmap_populate()
for kasan, as this memory does not go through struct page initialization
path.

Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Reviewed-by: Steven Sistare <steven.sistare@oracle.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: Bob Picco <bob.picco@oracle.com>
---
arch/arm64/mm/kasan_init.c | 42 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 42 insertions(+)

diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index 81f03959a4ab..e78a9ecbb687 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -135,6 +135,41 @@ static void __init clear_pgds(unsigned long start,
set_pgd(pgd_offset_k(start), __pgd(0));
}

+/*
+ * Memory that was allocated by vmemmap_populate is not zeroed, so we must
+ * zero it here explicitly.
+ */
+static void
+zero_vmemmap_populated_memory(void)
+{
+ struct memblock_region *reg;
+ u64 start, end;
+
+ for_each_memblock(memory, reg) {
+ start = __phys_to_virt(reg->base);
+ end = __phys_to_virt(reg->base + reg->size);
+
+ if (start >= end)
+ break;
+
+ start = (u64)kasan_mem_to_shadow((void *)start);
+ end = (u64)kasan_mem_to_shadow((void *)end);
+
+ /* Round to the start end of the mapped pages */
+ start = round_down(start, SWAPPER_BLOCK_SIZE);
+ end = round_up(end, SWAPPER_BLOCK_SIZE);
+ memset((void *)start, 0, end - start);
+ }
+
+ start = (u64)kasan_mem_to_shadow(_text);
+ end = (u64)kasan_mem_to_shadow(_end);
+
+ /* Round to the start end of the mapped pages */
+ start = round_down(start, SWAPPER_BLOCK_SIZE);
+ end = round_up(end, SWAPPER_BLOCK_SIZE);
+ memset((void *)start, 0, end - start);
+}
+
void __init kasan_init(void)
{
u64 kimg_shadow_start, kimg_shadow_end;
@@ -205,8 +240,15 @@ void __init kasan_init(void)
pfn_pte(sym_to_pfn(kasan_zero_page), PAGE_KERNEL_RO));

memset(kasan_zero_page, 0, PAGE_SIZE);
+
cpu_replace_ttbr1(lm_alias(swapper_pg_dir));

+ /*
+ * vmemmap_populate does not zero the memory, so we need to zero it
+ * explicitly
+ */
+ zero_vmemmap_populated_memory();
+
/* At this point kasan is fully initialized. Enable error messages */
init_task.kasan_depth = 0;
pr_info("KernelAddressSanitizer initialized\n");
--
2.14.0