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SubjectRe: [PATCH v8 10/11] arm64/kasan: explicitly zero kasan shadow memory
On Thu, Sep 14, 2017 at 06:35:16PM -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@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);
> +}

I really don't see the need to duplicate the existing logic to iterate over
memblocks, calculate the addresses, etc.

Why can't we just have a zeroing wrapper? e.g. something like the below.

I really don't see why we couldn't have a generic function in core code to do
this, even if vmemmap_populate() doesn't.

Thanks,
Mark.

---->8----
diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index 81f0395..698d065 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -135,6 +135,17 @@ static void __init clear_pgds(unsigned long start,
set_pgd(pgd_offset_k(start), __pgd(0));
}

+void kasan_populate_shadow(unsigned long shadow_start, unsigned long shadow_end,
+ nid_t nid)
+{
+ shadow_start = round_down(shadow_start, SWAPPER_BLOCK_SIZE);
+ shadow_end = round_up(shadow_end, SWAPPER_BLOCK_SIZE);
+
+ vmemmap_populate(shadow_start, shadow_end, nid);
+
+ memset((void *)shadow_start, 0, shadow_end - shadow_start);
+}
+
void __init kasan_init(void)
{
u64 kimg_shadow_start, kimg_shadow_end;
@@ -161,8 +172,8 @@ void __init kasan_init(void)

clear_pgds(KASAN_SHADOW_START, KASAN_SHADOW_END);

- vmemmap_populate(kimg_shadow_start, kimg_shadow_end,
- pfn_to_nid(virt_to_pfn(lm_alias(_text))));
+ kasah_populate_shadow(kimg_shadow_start, kimg_shadow_end,
+ pfn_to_nid(virt_to_pfn(lm_alias(_text))));

/*
* vmemmap_populate() has populated the shadow region that covers the
@@ -191,9 +202,9 @@ void __init kasan_init(void)
if (start >= end)
break;

- vmemmap_populate((unsigned long)kasan_mem_to_shadow(start),
- (unsigned long)kasan_mem_to_shadow(end),
- pfn_to_nid(virt_to_pfn(start)));
+ kasan_populate_shadow((unsigned long)kasan_mem_to_shadow(start),
+ (unsigned long)kasan_mem_to_shadow(end),
+ pfn_to_nid(virt_to_pfn(start)));
}

/*
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