Re: [V2][PATCH] asm-generic: sections: refactor memory_intersects

[Ard Biesheuvel]

On Fri, 19 Aug 2022 at 10:12, <quanyang.wang@xxxxxxxxxxxxx> wrote:
>
> From: Quanyang Wang <quanyang.wang@xxxxxxxxxxxxx>
>
> There are two problems with the current code of memory_intersects:
>
> First, it doesn't check whether the region (begin, end) falls inside
> the region (virt, vend), that is (virt < begin && vend > end).
>
> The second problem is if vend is equal to begin, it will return true
> but this is wrong since vend (virt + size) is not the last address of
> the memory region but (virt + size -1) is. The wrong determination will
> trigger the misreporting when the function check_for_illegal_area calls
> memory_intersects to check if the dma region intersects with stext region.
>
> The misreporting is as below (stext is at 0x80100000):
>  WARNING: CPU: 0 PID: 77 at kernel/dma/debug.c:1073 check_for_illegal_area+0x130/0x168
>  DMA-API: chipidea-usb2 e0002000.usb: device driver maps memory from kernel text or rodata [addr=800f0000] [len=65536]
>  Modules linked in:
>  CPU: 1 PID: 77 Comm: usb-storage Not tainted 5.19.0-yocto-standard #5
>  Hardware name: Xilinx Zynq Platform
>   unwind_backtrace from show_stack+0x18/0x1c
>   show_stack from dump_stack_lvl+0x58/0x70
>   dump_stack_lvl from __warn+0xb0/0x198
>   __warn from warn_slowpath_fmt+0x80/0xb4
>   warn_slowpath_fmt from check_for_illegal_area+0x130/0x168
>   check_for_illegal_area from debug_dma_map_sg+0x94/0x368
>   debug_dma_map_sg from __dma_map_sg_attrs+0x114/0x128
>   __dma_map_sg_attrs from dma_map_sg_attrs+0x18/0x24
>   dma_map_sg_attrs from usb_hcd_map_urb_for_dma+0x250/0x3b4
>   usb_hcd_map_urb_for_dma from usb_hcd_submit_urb+0x194/0x214
>   usb_hcd_submit_urb from usb_sg_wait+0xa4/0x118
>   usb_sg_wait from usb_stor_bulk_transfer_sglist+0xa0/0xec
>   usb_stor_bulk_transfer_sglist from usb_stor_bulk_srb+0x38/0x70
>   usb_stor_bulk_srb from usb_stor_Bulk_transport+0x150/0x360
>   usb_stor_Bulk_transport from usb_stor_invoke_transport+0x38/0x440
>   usb_stor_invoke_transport from usb_stor_control_thread+0x1e0/0x238
>   usb_stor_control_thread from kthread+0xf8/0x104
>   kthread from ret_from_fork+0x14/0x2c
>
> Refactor memory_intersects to fix the two problems above.
>
> Fixes: 979559362516 ("asm/sections: add helpers to check for section data")
> Signed-off-by: Quanyang Wang <quanyang.wang@xxxxxxxxxxxxx>
> ---
> V1 ---> V2:
> Add the consideration of the condition that one falls inside another
> which is noticed by Ard.
> ---
>  include/asm-generic/sections.h | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
> index d0f7bdd2fdf23..c51b3e7925cdf 100644
> --- a/include/asm-generic/sections.h
> +++ b/include/asm-generic/sections.h
> @@ -110,7 +110,10 @@ static inline bool memory_intersects(void *begin, void *end, void *virt,
>  {
>         void *vend = virt + size;
>
> -       return (virt >= begin && virt < end) || (vend >= begin && vend < end);
> +       if (virt < end && vend > begin)
> +               return true;
> +
> +       return false;
>  }
>

Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx>