Re: [PATCH] asm/sections: fix the determination of the end of the memory region

[Quanyang Wang]

Hi Ard,

On 8/11/22 16:16, Ard Biesheuvel wrote:
> On Thu, 11 Aug 2022 at 08:31, <quanyang.wang@xxxxxxxxxxxxx> wrote:
> > From: Quanyang Wang <quanyang.wang@xxxxxxxxxxxxx>
> >
> > If using "vend >= begin" to judge if two memory regions intersects, vend
> > should be the end of the memory region, so it should be "virt + size -1"
> > instead of "virt + size".
> > The wrong determination of the end triggers the misreporting as below when
> > the dma debug function "check_for_illegal_area" calls memory_intersects to
> > check if the dma region intersects with stext region.
> >
> > Calltrace (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
> >
> > Fixes: 979559362516 ("asm/sections: add helpers to check for section data")
> > Signed-off-by: Quanyang Wang <quanyang.wang@xxxxxxxxxxxxx>
> > ---
> >   include/asm-generic/sections.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
> > index d0f7bdd2fdf2..f7171b4f5bfd 100644
> > --- a/include/asm-generic/sections.h
> > +++ b/include/asm-generic/sections.h
> > @@ -108,7 +108,7 @@ static inline bool memory_contains(void *begin, void *end, void *virt,
> >   static inline bool memory_intersects(void *begin, void *end, void *virt,
> >                                       size_t size)
> >   {
> > -       void *vend = virt + size;
> > +       void *vend = virt + size - 1;
> >
> >          return (virt >= begin && virt < end) || (vend >= begin && vend < end);
>
> This test looks flawed to me for another reason as well: it only
> checks whether the start /or/ the end of (virt, virt+size) falls
> inside the area, so if the area is covered completely (in which case
> the intersection of the two will be equal to the area), this will
> return false erroneously.
Yes, the test lacks some checks. I will send a V2 patch to fix it.
Thanks,
Quanyang