Re: [PATCH] bootconfig: use memblock_free_late to free xbc memory to buddy

[Qiang Zhang]

On Fri, Apr 12, 2024 at 10:03:26AM +0800, qiang4.zhang@xxxxxxxxxxxxxxx wrote:
>From: Qiang Zhang <qiang4.zhang@xxxxxxxxx>
>
>On the time to free xbc memory, memblock has handed over memory to buddy
>allocator. So it doesn't make sense to free memory back to memblock.
>memblock_free() called by xbc_exit() even causes UAF bugs on architectures
>with CONFIG_ARCH_KEEP_MEMBLOCK disabled like x86. Following KASAN logs
>shows this case.
>
>[    9.410890] ==================================================================
>[    9.418962] BUG: KASAN: use-after-free in memblock_isolate_range+0x12d/0x260
>[    9.426850] Read of size 8 at addr ffff88845dd30000 by task swapper/0/1
>
>[    9.435901] CPU: 9 PID: 1 Comm: swapper/0 Tainted: G     U             6.9.0-rc3-00208-g586b5dfb51b9 #5
>[    9.446403] Hardware name: Intel Corporation RPLP LP5 (CPU:RaptorLake)/RPLP LP5 (ID:13), BIOS IRPPN02.01.01.00.00.19.015.D-00000000 Dec 28 2023
>[    9.460789] Call Trace:
>[    9.463518]  <TASK>
>[    9.465859]  dump_stack_lvl+0x53/0x70
>[    9.469949]  print_report+0xce/0x610
>[    9.473944]  ? __virt_addr_valid+0xf5/0x1b0
>[    9.478619]  ? memblock_isolate_range+0x12d/0x260
>[    9.483877]  kasan_report+0xc6/0x100
>[    9.487870]  ? memblock_isolate_range+0x12d/0x260
>[    9.493125]  memblock_isolate_range+0x12d/0x260
>[    9.498187]  memblock_phys_free+0xb4/0x160
>[    9.502762]  ? __pfx_memblock_phys_free+0x10/0x10
>[    9.508021]  ? mutex_unlock+0x7e/0xd0
>[    9.512111]  ? __pfx_mutex_unlock+0x10/0x10
>[    9.516786]  ? kernel_init_freeable+0x2d4/0x430
>[    9.521850]  ? __pfx_kernel_init+0x10/0x10
>[    9.526426]  xbc_exit+0x17/0x70
>[    9.529935]  kernel_init+0x38/0x1e0
>[    9.533829]  ? _raw_spin_unlock_irq+0xd/0x30
>[    9.538601]  ret_from_fork+0x2c/0x50
>[    9.542596]  ? __pfx_kernel_init+0x10/0x10
>[    9.547170]  ret_from_fork_asm+0x1a/0x30
>[    9.551552]  </TASK>
>
>[    9.555649] The buggy address belongs to the physical page:
>[    9.561875] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x45dd30
>[    9.570821] flags: 0x200000000000000(node=0|zone=2)
>[    9.576271] page_type: 0xffffffff()
>[    9.580167] raw: 0200000000000000 ffffea0011774c48 ffffea0012ba1848 0000000000000000
>[    9.588823] raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
>[    9.597476] page dumped because: kasan: bad access detected
>
>[    9.605362] Memory state around the buggy address:
>[    9.610714]  ffff88845dd2ff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>[    9.618786]  ffff88845dd2ff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>[    9.626857] >ffff88845dd30000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>[    9.634930]                    ^
>[    9.638534]  ffff88845dd30080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>[    9.646605]  ffff88845dd30100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>[    9.654675] ==================================================================

Sorry. Forget to Cc stable. Will send a new one.

>
>Signed-off-by: Qiang Zhang <qiang4.zhang@xxxxxxxxx>
>---
> lib/bootconfig.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/lib/bootconfig.c b/lib/bootconfig.c
>index c59d26068a64..4524ee944df0 100644
>--- a/lib/bootconfig.c
>+++ b/lib/bootconfig.c
>@@ -63,7 +63,7 @@ static inline void * __init xbc_alloc_mem(size_t size)
> 
> static inline void __init xbc_free_mem(void *addr, size_t size)
> {
>-	memblock_free(addr, size);
>+	memblock_free_late(__pa(addr), size);
> }
> 
> #else /* !__KERNEL__ */
>-- 
>2.39.2
>