haitomatic commented on PR #17161:
URL: https://github.com/apache/nuttx/pull/17161#issuecomment-3479404800
@tinnedkarma , yes I meant the protected mode which is built with
`nuttx/boards/risc-v/mpfs/icicle/configs/knsh/defconfig` ,
I think there is some issue when copying from user space buffer to kernel
space buffer
```
User space: cansend → write() → sendmsg()
↓ (system call boundary)
Kernel space: sendmsg() → psock_sendmsg() → can_sendmsg()
↓
can_sendmsg(): devif_send(dev, pstate->snd_buffer, ...)
↓
devif_send(): iob_trycopyin(dev->d_iob, buf, len, offset, false)
↓
iob_trycopyin(): iob_copyin_internal(...)
↓
iob_copyin_internal(): memcpy(dest, src, ncopy) ← **FAILURE POINT**
```
The issue isn't that user space memory is completely inaccessible, but
rather:
- Race conditions between user and kernel space
- Cache coherency problems
- MMU mapping consistency issues
Anyhow, this issue is not in the scope of this PR, I would say since it
works well now with flat mode, I would love to merge it :)
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