From 9e46e4dcd9d6cd88342b028dbfa5f4fb7483d39c Mon Sep 17 00:00:00 2001 From: Rik van Riel Date: Wed, 19 Jul 2023 15:41:37 -0400 Subject: 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 Link: https://lore.kernel.org/r/20230719154137.732d8525@imladris.surriel.com Signed-off-by: Mike Rapoport (IBM) --- mm/memblock.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'mm/memblock.c') diff --git a/mm/memblock.c b/mm/memblock.c index f9e61e565a53..c39b36378f5d 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) { -- cgit v1.2.3