tree c83aa3de1e423a8793e0672d9cfab3973a9321bd
parent 683f2554083d17ae8cb65de5eea9bcaa4f9a867b
author Jonas Larsson <ljonas@google.com> 1570649580 -0700
committer June Tate-Gans <jtgans@google.com> 1570667075 -0500

fdmem: always map dmabuf with PROT_WRITE

This is to enable zero copy inference on dmabufs. Gasket kernel driver
requires all user pointers passed to it to be writable in
drivers/staging/gasket/gasket_page_table.c gasket_perform_mapping
even if it's not actually writing to the buffer. If we map a buffer
with GST_MAP_READ it'll be mmapped with PROT_READ and gasket will
error out with -EFAULT.

While a more correct solution is to fix the gasket driver the needed
linux/mm APIs aren't there in the current version of the kernel.
We'd need
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=73b0140bf0fe9df90fb267c00673c4b9bf285430
which is for a much later kernel version.

This change may look dangerous but what it really does is to make
dmabuf protection equal to buffers allocated by the system memory
allocator; i.e. even if you map a buffer with GST_MAP_READ only
you can, but should not, write to it.

BUG: 142164990

Change-Id: Ie615f923c44969a3606d8856311ffe853a0dd742