Re: [PATCH v2] arm64/module: use plt section indices for relocations

[Will Deacon]

On Mon, Nov 05, 2018 at 07:53:23PM +0100, Jessica Yu wrote:
> Instead of saving a pointer to the .plt and .init.plt sections to apply
> plt-based relocations, save and use their section indices instead.
> 
> The mod->arch.{core,init}.plt pointers were problematic for livepatch
> because they pointed within temporary section headers (provided by the
> module loader via info->sechdrs) that would be freed after module load.
> Since livepatch modules may need to apply relocations post-module-load
> (for example, to patch a module that is loaded later), using section
> indices to offset into the section headers (instead of accessing them
> through a saved pointer) allows livepatch modules on arm64 to pass in
> their own copy of the section headers to apply_relocate_add() to apply
> delayed relocations.
> 
> Signed-off-by: Jessica Yu <jeyu@xxxxxxxxxx>
> ---
> 
> v2:
> 
> - Do sechdrs[pltsec->plt_shndx].sh_addr instead of pointer math
> 
> Note: Addressed Will's comment about the pltsec -> plt_info rename and
> removed that change to reduce unnecessary code churn. I didn't include the
> Ack's for this reason so let me know if this version is OK as well.

Thanks, Jessica!

Acked-by: Will Deacon <will.deacon@xxxxxxx>

> arch/arm64/include/asm/module.h |  8 +++++---
> arch/arm64/kernel/module-plts.c | 36 ++++++++++++++++++++----------------
> arch/arm64/kernel/module.c      |  9 +++++----
> 3 files changed, 30 insertions(+), 23 deletions(-)

Actually, I guess I should just queue this for 4.21 given that it's
completely self-contained.

Will