[PATCH v2 0/1] Add ro_after_init support for modules

From: Jessica Yu
Date: Mon Jul 25 2016 - 05:26:27 EST


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
* 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.

v1 here:

- Add a bool after_init parameter to module_enable_ro(), it's much clearer
than checking module->state.
- Since the function signature for module_enable_ro() has changed, livepatch
needs to slightly adjust its call to module_enable_ro()

Jessica Yu (1):
modules: add ro_after_init support

include/linux/module.h | 6 +++--
include/uapi/linux/elf.h | 1 +
kernel/livepatch/core.c | 2 +-
kernel/module.c | 66 +++++++++++++++++++++++++++++++++++++++---------
4 files changed, 60 insertions(+), 15 deletions(-)