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

[Qiang Zhang]

On Fri, Apr 12, 2024 at 04:34:48PM +0900, Masami Hiramatsu wrote:
>On Fri, 12 Apr 2024 10:41:04 +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] ==================================================================
>> 
>
>Oops, good catch! Indeed, it is too late to use memblock_free().
>
>BTW, is it safe to call memblock_free_late() in early boot stage,
>because xbc_free_mem() will be called also from xbc_init().
>If not, we need a custom internal __xbc_exit() or xbc_cleanup()
>which is called from xbc_init() and uses memblock_free().

No, memblock_free_late() can't be used early.
Exit and Cleanup seem alike and are confusing. Maybe adding a early flag to
_xbc_exit(bool early) is more clear. I will push a V2 for this.

>
>Thank you,
>
>
>> Cc: Stable@xxxxxxxxxxxxxxx
>> 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
>> 
>> 
>
>
>-- 
>Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>