Hi folks,
Could you please share your comments on v8 patch?
Thanks,
Song
On Fri, Jan 6, 2023 at 12:01 PM Song Liu <song@xxxxxxxxxx> wrote:
>
> From: Miroslav Benes <mbenes@xxxxxxx>
>
> 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 deny the patched modules to be removed. If it proved to be
> a major drawback for users, we could still implement a different
> approach. The solution would also complicate the existing code a lot.
>
> We thus decided to reverse the relocation patching (clear all relocation
> targets on x86_64). The solution is not
> universal and is too much arch-specific, but it may prove to be simpler
> in the end.
>
> Signed-off-by: Miroslav Benes <mbenes@xxxxxxx>
> Signed-off-by: Song Liu <song@xxxxxxxxxx>
> Reported-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
>
> ---
>
> NOTE: powerpc32 code is only compile tested.
>
> Changes v7 = v8:
> 1. Remove the logic in powerpc/kernel/module_64.c, as there is ongoing
> discussions.
> 2. For x86_64, add check for expected value during clear_relocate_add().
> (Petr Mladek)
> 3. Optimize the logic in klp_write_section_relocs(). (Petr Mladek)
> 4. Optimize __write_relocate_add (x86_64). (Joe Lawrence)
>
> Changes v6 = v7:
> 1. Reduce code duplication in livepatch/core.c and x86/kernel/module.c.
> 2. Add more comments to powerpc/kernel/module_64.c.
> 3. Added Joe's Tested-by (which I should have added in v6).
[...]
