Messages in this thread | | | From | Jessica Yu <> | Subject | [PATCH 0/1] Add ro_after_init support for modules | Date | Mon, 13 Jun 2016 20:13:17 -0400 |
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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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