With this patch clients of the RM service can state if they want a mapping
to be executable or not. This allows dataspaces to be mapped as
non-executable on Linux by default and as executable only if needed.
Partially fixes#176.
When using an ELF image as returned from the iso9660 server, such an
image is represented as a managed dataspace composed of various portions
of one RAM dataspace, each portion attached with a different offset.
Now, when mapping the text segment of the ELF image (usually starting at
0x1000 within the image), the code mapped at 0x1000 may correspond to
any offset within the RAM dataspace used by the iso9660 server. In
particular, the src-fault address (the one within the RAM dataspace) may
be higher than dst-fault address (somewhere just above 0x1000 where a
page-fault occurred). Thereby, 'curr_rm_base' may become negative
during the reverse lookup of 'Rm_client::pager'. This corner case used
to let the 'Fault_area::constrain' function return an invalid fault
area, and thereby let the reverse lookup fail. The improved version
explicitly checks for the address overflow condition and tries to
constrain the dst fault address to the largest possible log2 page within
the positive address range.
Christian Prochaska
Norman Feske
Genode Labs