Hi,
This patch adds ro_after_init support for modules by adding an additional
page-aligned section in the module layout. This new ro_after_init section
sits between rodata and writable data.
So, the new module layout looks like:
[text] [rodata] [ro_after_init] [writable data]
RO after init data remains RW during init and RO protection is enabled
separately after module init runs.
Did some light testing with lkdtm compiled as a module, verified that
ro_after_init data is writable during init, and that it oopsed after attempted
writes after init. Also tested livepatch (which uses module_{enable,disable}_ro
for its own purposes) to make sure nothing broke. More testing is appreciated :-)
Some remarks on the implementation:
* A new SHF_RO_AFTER_INIT flag is introduced in elf.h to make
identification of .data..ro_after_init sections and the work of
layout_sections() easier. Its chosen value is within the SHF_MASKOS
range. If people don't like adding a new SHF flag to elf.h, I could
just make the flag internal to module.c.
* frob_ro_after_init() could have been separated from
module_enable_ro() (i.e., put it in its own function, something
like module_enable_ro_after_init()), but given that livepatch also
uses module_enable_ro(), I did not want to make livepatch worry
about calling yet another function just to re-enable all RO protections
for a module.
* If a module doesn't have a ro_after_init section, then
core_layout.ro_after_init_size just takes the value of
core_layout.ro_size, and frob_ro_after_init() should do nothing.
Based on linux-next.
Previous discussion here:
http://comments.gmane.org/gmane.linux.kernel/2234606
Jessica Yu (1):
modules: add ro_after_init support
include/linux/module.h | 2 ++
include/uapi/linux/elf.h | 1 +
kernel/module.c | 73 +++++++++++++++++++++++++++++++++++++++++-------
3 files changed, 66 insertions(+), 10 deletions(-)
--
2.4.3
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