On Tue, 2021-06-22 at 11:01 +0200, Marco Elver wrote:

On Tue, 22 Jun 2021 at 10:48, [off-list ref] wrote:

quoted

From: Yee Lee <redacted>

Follows the discussion: 
https://patchwork.kernel.org/project/linux-mediatek/list/?series=504439

The info about the percentage of how frequent this is could have been
provided as a simple reply to the discussion.

quoted

This patch Add memzero_explict to initialize unaligned object.

This patch does not apply to anything (I see it depends on the
previous patch).

What you need to do is modify the original patch, and then send a
[PATCH v2] (git helps with that by passing --reroll-count or -v) that
applies cleanly to your base kernel tree.

The commit message will usually end with '---' and then briefly
denote
what changed since the last version.

Got it.

https://www.kernel.org/doc/html/latest/process/submitting-patches.html#the-canonical-patch-format

quoted

Based on the integrateion of initialization in kasan_unpoison().
The hwtag instructions, constrained with its granularity, has to
overwrite the data btyes in unaligned objects. This would cause
issue when it works with SLUB debug redzoning.

In this patch, an additional initalizaing path is added for the
unaligned objects. It contains memzero_explict() to clear out the
data and disables its init flag for the following hwtag actions.

In lab test, this path is executed about 1.1%(941/80854) within the
overall kasan_unpoison during a non-debug booting process.

Nice, thanks for the data. If it is somehow doable, however, I'd
still
recommend to additionally guard the new code path by a check if
debug-support was requested. Ideally with an IS_ENABLED() config
check
so that if it's a production kernel the branch is simply optimized
out
by the compiler.

Does it mean the memzero code path would be applied only at
CONFIG_DEBUG_SLUB enabled? It expects no other potential overwriting
in non-debug kernel.
 
By the way, based on de-coupling principle, adding a specific
conditional statement(is_enable slub_debug) in a primitive
funciton(kasan_unpoison) is not neat. It may be more proper that the
conditional statement be added in other procedures of slub alloc.
 
Thanks,

BR,
Yee

quoted

Lab test: QEMU5.2 (+mte) / linux kernel 5.13-rc7

Signed-off-by: Yee Lee <redacted>
---
 mm/kasan/kasan.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index d8faa64614b7..edc11bcc3ff3 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h

@@ -389,7 +389,7 @@ static inline void kasan_unpoison(const void

*addr, size_t size, bool init)
                return;
        if (init && ((unsigned long)size & KASAN_GRANULE_MASK)) {
                init = false;
-               memset((void *)addr, 0, size);
+               memzero_explicit((void *)addr, size);
        }
        size = round_up(size, KASAN_GRANULE_SIZE);
        hw_set_mem_tag_range((void *)addr, size, tag, init);
2.18.0

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