From: "Mike Rapoport (Microsoft)" <[email protected]> When CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled, freeing of reserved memory before the memory map is fully initialized in deferred_init_memmap() would cause access to uninitialized struct pages and may crash when accessing spurious list pointers, like was recently discovered during discussion about memory leaks in x86 EFI code [1].
The trace below is from an attempt to call free_reserved_page() before page_alloc_init_late(): [ 0.076840] BUG: unable to handle page fault for address: ffffce1a005a0788 [ 0.078226] #PF: supervisor read access in kernel mode [ 0.078226] #PF: error_code(0x0000) - not-present page [ 0.078226] PGD 0 P4D 0 [ 0.078226] Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI [ 0.078226] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.12.68-92.123.amzn2023.x86_64 #1 [ 0.078226] Hardware name: Amazon EC2 t3a.nano/, BIOS 1.0 10/16/2017 [ 0.078226] RIP: 0010:__list_del_entry_valid_or_report+0x32/0xb0 ... [ 0.078226] __free_one_page+0x170/0x520 [ 0.078226] free_pcppages_bulk+0x151/0x1e0 [ 0.078226] free_unref_page_commit+0x263/0x320 [ 0.078226] free_unref_page+0x2c8/0x5b0 [ 0.078226] ? srso_return_thunk+0x5/0x5f [ 0.078226] free_reserved_page+0x1c/0x30 [ 0.078226] memblock_free_late+0x6c/0xc0 Currently there are not many callers of free_reserved_area() and they all appear to be at the right timings. Still, in order to protect against problematic code moves or additions of new callers add a warning that will inform that reserved pages cannot be freed until the memory map is fully initialized. [1] https://lore.kernel.org/all/e5d5a1105d90ee1e7fe7eafaed2ed03bbad0c46b.ca...@kernel.crashing.org/ Signed-off-by: Mike Rapoport (Microsoft) <[email protected]> --- mm/internal.h | 10 ++++++++++ mm/memblock.c | 5 +++++ mm/page_alloc.c | 10 ---------- 3 files changed, 15 insertions(+), 10 deletions(-) diff --git a/mm/internal.h b/mm/internal.h index cb0af847d7d9..f60c1edb2e02 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -1233,7 +1233,17 @@ static inline void vunmap_range_noflush(unsigned long start, unsigned long end) #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT DECLARE_STATIC_KEY_TRUE(deferred_pages); +static inline bool deferred_pages_enabled(void) +{ + return static_branch_unlikely(&deferred_pages); +} + bool __init deferred_grow_zone(struct zone *zone, unsigned int order); +#else +static inline bool deferred_pages_enabled(void) +{ + return false; +} #endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */ void init_deferred_page(unsigned long pfn, int nid); diff --git a/mm/memblock.c b/mm/memblock.c index bd5758ff07f2..780e70d4971a 100644 --- a/mm/memblock.c +++ b/mm/memblock.c @@ -896,6 +896,11 @@ static unsigned long __free_reserved_area(phys_addr_t start, phys_addr_t end, { unsigned long pages = 0, pfn; + if (deferred_pages_enabled()) { + WARN(1, "Cannot free reserved memory because of deferred initialization of the memory map"); + return 0; + } + for_each_valid_pfn(pfn, PFN_UP(start), PFN_DOWN(end)) { struct page *page = pfn_to_page(pfn); void *direct_map_addr; diff --git a/mm/page_alloc.c b/mm/page_alloc.c index df3d61253001..9ac47bab2ea7 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -331,11 +331,6 @@ int page_group_by_mobility_disabled __read_mostly; */ DEFINE_STATIC_KEY_TRUE(deferred_pages); -static inline bool deferred_pages_enabled(void) -{ - return static_branch_unlikely(&deferred_pages); -} - /* * deferred_grow_zone() is __init, but it is called from * get_page_from_freelist() during early boot until deferred_pages permanently @@ -348,11 +343,6 @@ _deferred_grow_zone(struct zone *zone, unsigned int order) return deferred_grow_zone(zone, order); } #else -static inline bool deferred_pages_enabled(void) -{ - return false; -} - static inline bool _deferred_grow_zone(struct zone *zone, unsigned int order) { return false; -- 2.51.0
