physmem: Is 0644 OK for new created file?

[Peng Liang]

Hi,

Recently, I tried to use ivshmem-plain devices to share some information
between guests.  I found that if the file of the shmem doesn't exist,
then QEMU will create one and the mode of it is 0644.  Maybe it is risky
because everyone can read the content of the file?  Do we need to change
it to 0640 or 0600?

Thanks,
Peng