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().
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>
