[PATCH] regmap: maple: Fix cache corruption in regcache_maple_drop()

[Richard Fitzgerald]

When keeping the upper end of a cache block entry, the entry[] array
must be indexed by the offset from the base register of the block,
i.e. max - mas.index.

The code was indexing entry[] by only the register address, leading
to an out-of-bounds access that copied some part of the kernel
memory over the cache contents.

This bug was not detected by the regmap KUnit test because it only
tests with a block of registers starting at 0, so mas.index == 0.

Signed-off-by: Richard Fitzgerald <rf@xxxxxxxxxxxxxxxxxxxxx>
Fixes: f033c26de5a5 ("regmap: Add maple tree based register cache")
---
 drivers/base/regmap/regcache-maple.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/base/regmap/regcache-maple.c b/drivers/base/regmap/regcache-maple.c
index 41edd6a430eb..c1776127a572 100644
--- a/drivers/base/regmap/regcache-maple.c
+++ b/drivers/base/regmap/regcache-maple.c
@@ -145,7 +145,7 @@ static int regcache_maple_drop(struct regmap *map, unsigned int min,
 			upper_index = max + 1;
 			upper_last = mas.last;
 
-			upper = kmemdup(&entry[max + 1],
+			upper = kmemdup(&entry[max - mas.index + 1],
 					((mas.last - max) *
 					 sizeof(unsigned long)),
 					map->alloc_flags);
-- 
2.39.2