Re: [PATCH 1/1] ACPI: fix acpi table use after free

[George Kennedy <george.kennedy@oracle.com>]

Hello Rafael,

On 3/4/2021 7:14 AM, Rafael J. Wysocki wrote:
> On Thu, Mar 4, 2021 at 2:22 AM George Kennedy <george.kennedy@oracle.com> wrote:
>> Since commit 7fef431be9c9 ("mm/page_alloc: place pages to tail
>> in __free_pages_core()") the following use after free occurs
>> intermittently when acpi tables are accessed.
>>
>> BUG: KASAN: use-after-free in ibft_init+0x134/0xc49
>> Read of size 4 at addr ffff8880be453004 by task swapper/0/1
>> CPU: 3 PID: 1 Comm: swapper/0 Not tainted 5.12.0-rc1-7a7fd0d #1
>> Call Trace:
>>   dump_stack+0xf6/0x158
>>   print_address_description.constprop.9+0x41/0x60
>>   kasan_report.cold.14+0x7b/0xd4
>>   __asan_report_load_n_noabort+0xf/0x20
>>   ibft_init+0x134/0xc49
>>   do_one_initcall+0xc4/0x3e0
>>   kernel_init_freeable+0x5af/0x66b
>>   kernel_init+0x16/0x1d0
>>   ret_from_fork+0x22/0x30
>>
>> ACPI tables mapped via kmap() do not have their mapped pages
>> reserved and the pages can be "stolen" by the buddy allocator.
> What do you mean by this?
The ibft table, for example, is mapped in via acpi_map() and kmap(). The 
page for the ibft table is not reserved, so it can end up on the freelist.
>
>> Use memblock_reserve() to reserve all the ACPI table pages.
> How is this going to help?
If the ibft table page is not reserved, it will end up on the freelist 
and potentially be allocated before ibft_init() is called.

I believe this is the call that causes the ibft table page (in this case 
pfn=0xbe453) to end up on the freelist:

memmap_init_range: size=bd49b, nid=0, zone=1, start_pfn=1000, 
zone_end_pfn=100000

[    0.477319]  memmap_init_range+0x33b/0x4e2
[    0.479053]  memmap_init_zone+0x1e0/0x243
[    0.485276]  free_area_init_node+0xa4e/0xac5
[    0.498242]  free_area_init+0xf4a/0x107a
[    0.509958]  zone_sizes_init+0xd9/0x111
[    0.511731]  paging_init+0x4a/0x4c
[    0.512417]  setup_arch+0x14f8/0x1758
[    0.519193]  start_kernel+0x6c/0x46f
[    0.519921]  x86_64_start_reservations+0x37/0x39
[    0.520847]  x86_64_start_kernel+0x7b/0x7e
[    0.521666]  secondary_startup_64_no_verify+0xb0/0xbb

>
>> Signed-off-by: George Kennedy <george.kennedy@oracle.com>
>> ---
>>   arch/x86/kernel/setup.c        | 3 +--
>>   drivers/acpi/acpica/tbinstal.c | 4 ++++
>>   2 files changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
>> index d883176..97deea3 100644
>> --- a/arch/x86/kernel/setup.c
>> +++ b/arch/x86/kernel/setup.c
>> @@ -1046,6 +1046,7 @@ void __init setup_arch(char **cmdline_p)
>>          cleanup_highmap();
>>
>>          memblock_set_current_limit(ISA_END_ADDRESS);
>> +       acpi_boot_table_init();
> This cannot be moved before the acpi_table_upgrade() invocation AFAICS.
>
> Why exactly do you want to move it?

Want to make sure there are slots for memblock_reserve() to be able to 
reserve the page.
>
>>          e820__memblock_setup();
>>
>>          /*
>> @@ -1139,8 +1140,6 @@ void __init setup_arch(char **cmdline_p)
>>          /*
>>           * Parse the ACPI tables for possible boot-time SMP configuration.
>>           */
>> -       acpi_boot_table_init();
>> -
>>          early_acpi_boot_init();
>>
>>          initmem_init();
>> diff --git a/drivers/acpi/acpica/tbinstal.c b/drivers/acpi/acpica/tbinstal.c
>> index 8d1e5b5..4e32b22 100644
>> --- a/drivers/acpi/acpica/tbinstal.c
>> +++ b/drivers/acpi/acpica/tbinstal.c
>> @@ -8,6 +8,7 @@
>>    *****************************************************************************/
>>
>>   #include <acpi/acpi.h>
>> +#include <linux/memblock.h>
>>   #include "accommon.h"
>>   #include "actables.h"
>>
>> @@ -58,6 +59,9 @@
>>                                        new_table_desc->flags,
>>                                        new_table_desc->pointer);
>>
>> +       memblock_reserve(new_table_desc->address,
>> +                        PAGE_ALIGN(new_table_desc->pointer->length));
>> +
> Why do you want to do this here in the first place?

If there is a better place to do it, I can move the memblock_reserve() 
there. The memblock_reserve() cannot be done from the ibft code - it's 
too late - the ibft table page has already ended up on the freelist by 
the time ibft_init() is called.

>
> Things like that cannot be done in the ACPICA code in general.

Can you recommend a better place to do the memblock_reserve() from?

Thank you,
George

>
>>          acpi_tb_print_table_header(new_table_desc->address,
>>                                     new_table_desc->pointer);
>>
>> --