Re: [v6 11/15] arm64/kasan: explicitly zero kasan shadow memory
From: Pasha Tatashin
Date: Tue Aug 08 2017 - 07:50:54 EST
Hi Will,
Thank you for looking at this change. What you described was in my
previous iterations of this project.
See for example here: https://lkml.org/lkml/2017/5/5/369
I was asked to remove that flag, and only zero memory in place when
needed. Overall the current approach is better everywhere else in the
kernel, but it adds a little extra code to kasan initialization.
Pasha
On 08/08/2017 05:07 AM, Will Deacon wrote:
On Mon, Aug 07, 2017 at 04:38:45PM -0400, Pavel Tatashin wrote:
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@xxxxxxxxxx>
Reviewed-by: Steven Sistare <steven.sistare@xxxxxxxxxx>
Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Reviewed-by: Bob Picco <bob.picco@xxxxxxxxxx>
---
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);
+}
I can't help but think this would be an awful lot nicer if you made
vmemmap_alloc_block take extra GFP flags as a parameter. That way, we could
implement a version of vmemmap_populate that does the zeroing when we need
it, without having to duplicate a bunch of the code like this. I think it
would also be less error-prone, because you wouldn't have to do the
allocation and the zeroing in two separate steps.
Will