Quoting the second patch's changelog:
Josh reported a bug:
When the object to be patched is a module, and that module is
rmmod'ed and reloaded, it fails to load with:
module: x86/modules: Skipping invalid relocation target, existing value is nonzero for type 2, loc 00000000ba0302e9, val ffffffffa03e293c
livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8)
livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd'
The livepatch module has a relocation which references a symbol
in the _previous_ loading of nfsd. When apply_relocate_add()
tries to replace the old relocation with a new one, it sees that
the previous one is nonzero and it errors out.
On ppc64le, we have a similar issue:
module_64: livepatch_nfsd: Expected nop after call, got e8410018 at e_show+0x60/0x548 [livepatch_nfsd]
livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8)
livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd'
He also proposed three different solutions. We could remove the error
check in apply_relocate_add() introduced by commit eda9cec4c9a1
("x86/module: Detect and skip invalid relocations"). However the check
is useful for detecting corrupted modules.
We could also reverse the relocation patching (clear all relocation
targets on x86_64, or return back nops on powerpc) in
klp_unpatch_object(). The solution is not universal and is too much
arch-specific.
We decided to deny the patched modules to be removed. If it proves to be
a major drawback for users, we can still implement a different approach.
There were many subtle details to check, so it may be broken somewhere.
Hopefully it is not, but please review carefully.
Miroslav Benes (3):
livepatch: Nullify obj->mod in klp_module_coming()'s error path
livepatch: Deny the patched modules to be removed
module: Remove superfluous call to klp_module_going()
kernel/livepatch/core.c | 25 +++++++++++++++++++++++--
kernel/module.c | 1 -
2 files changed, 23 insertions(+), 3 deletions(-)
--
2.17.0
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