[PATCH] arm64: Fix map_range() not splitting mapped blocks

[Pierre-Clément Tosi]

The implementation of map_range() creates the requested mapping by
walking the page tables, iterating over multiple PTEs and/or descending
into existing table mappings as needed. When doing so, it assumes any
pre-existing valid PTE to be a table mapping. This assumption is wrong
if the platform code attempts to successively map two overlapping ranges
where the latter intersects a block mapping created for the former.

As a result, map_range() treats the existing block mapping as a table
mapping and descends into it i.e. starts interpreting the
previously-mapped range as an array of PTEs, writing to them and
potentially even descending further (extra fun with MMIO ranges!).

Instead, pass any valid non-table mapping to split_block(), which
ensures that it actually was a block mapping (calls panic() otherwise)
before splitting it.

Fixes: 41e2787f5ec4 ("arm64: Reduce add_map() complexity")
Signed-off-by: Pierre-Clément Tosi <ptosi at google.com>
---
 arch/arm/cpu/armv8/cache_v8.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm/cpu/armv8/cache_v8.c b/arch/arm/cpu/armv8/cache_v8.c
index 697334086f..57d06f0575 100644
--- a/arch/arm/cpu/armv8/cache_v8.c
+++ b/arch/arm/cpu/armv8/cache_v8.c
@@ -326,6 +326,8 @@ static void map_range(u64 virt, u64 phys, u64 size, int level,
 		/* Going one level down */
 		if (pte_type(&table[i]) == PTE_TYPE_FAULT)
 			set_pte_table(&table[i], create_table());
+		else if (pte_type(&table[i]) != PTE_TYPE_TABLE)
+			split_block(&table[i], level);
 
 		next_table = (u64 *)(table[i] & GENMASK_ULL(47, PAGE_SHIFT));
 		next_size = min(map_size - (virt & (map_size - 1)), size);
-- 
2.44.0.291.gc1ea87d7ee-goog


-- 
Pierre