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

[quanyang . wang]

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;
 }
 
 /**
-- 
2.36.1