From 9e46e4dcd9d6cd88342b028dbfa5f4fb7483d39c Mon Sep 17 00:00:00 2001
From: Rik van Riel <riel@surriel.com>
Date: Wed, 19 Jul 2023 15:41:37 -0400
Subject: [PATCH] mm,memblock: reset memblock.reserved to system init state to
prevent UAF
The memblock_discard function frees the memblock.reserved.regions
array, which is good.
However, if a subsequent memblock_free (or memblock_phys_free) comes
in later, from for example ima_free_kexec_buffer, that will result in
a use after free bug in memblock_isolate_range.
When running a kernel with CONFIG_KASAN enabled, this will cause a
kernel panic very early in boot. Without CONFIG_KASAN, there is
a chance that memblock_isolate_range might scribble on memory
that is now in use by somebody else.
Avoid those issues by making sure that memblock_discard points
memblock.reserved.regions back at the static buffer.
If memblock_free is called after memblock memory is discarded, that will
print a warning in memblock_remove_region.
Signed-off-by: Rik van Riel <riel@surriel.com>
Link: https://lore.kernel.org/r/20230719154137.732d8525@imladris.surriel.com
Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
---
mm/memblock.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/mm/memblock.c b/mm/memblock.c
index f9e61e565a534..c39b36378f5dd 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -374,6 +374,10 @@ void __init memblock_discard(void)
kfree(memblock.reserved.regions);
else
memblock_free_late(addr, size);
+ /* Reset to prevent UAF from stray frees. */
+ memblock.reserved.regions = memblock_reserved_init_regions;
+ memblock.reserved.cnt = 1;
+ memblock_remove_region(&memblock.reserved, 0);
}
if (memblock.memory.regions != memblock_memory_init_regions) {