On Fri, Aug 5, 2022 at 1:58 PM Joe Lawrence <joe.lawrence@xxxxxxxxxx> wrote:
>
> On Mon, Aug 01, 2022 at 02:21:29PM -0700, Song Liu 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.
> >
> > Reported-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> > Signed-off-by: Miroslav Benes <mbenes@xxxxxxx>
> > Signed-off-by: Song Liu <song@xxxxxxxxxx>
> >
> > ---
> >
> > NOTE: powerpc code has not be tested.
> >
>
> Hi Song,
>
> I just want to provide a quick check in on this patch...
>
> First -- what tree / commit should this be based on? When I add this
> patch on top of a v5.19 based tree, I see:
>
> arch/powerpc/kernel/module_64.c: In function ‘clear_relocate_add’:
> arch/powerpc/kernel/module_64.c:781:52: error: incompatible type for argument 1 of ‘instr_is_relative_link_branch’
> 781 | if (!instr_is_relative_link_branch(*instruction))
> | ^~~~~~~~~~~~
> | |
> | u32 {aka unsigned int}
> In file included from arch/powerpc/kernel/module_64.c:20:
> ./arch/powerpc/include/asm/code-patching.h:122:46: note: expected ‘ppc_inst_t’ but argument is of type ‘u32’ {aka ‘unsigned int’}
> 122 | int instr_is_relative_link_branch(ppc_inst_t instr);
> | ~~~~~~~~~~~^~~~~
> arch/powerpc/kernel/module_64.c:785:32: error: ‘PPC_INST_NOP’ undeclared (first use in this function); did you mean ‘PPC_INST_COPY’?
> 785 | *instruction = PPC_INST_NOP;
> | ^~~~~~~~~~~~
> | PPC_INST_COPY
> arch/powerpc/kernel/module_64.c:785:32: note: each undeclared identifier is reported only once for each function it appears in
> make[2]: *** [scripts/Makefile.build:249: arch/powerpc/kernel/module_64.o] Error 1
> make[1]: *** [scripts/Makefile.build:466: arch/powerpc/kernel] Error 2
> make: *** [Makefile:1849: arch/powerpc] Error 2
>
I am sorry that I didn't build the PPC code. (I did fix some code, but
I guess that's
not enough. ) I was hoping kernel test bot to run build tests on the
patch, but I
guess the bot is not following live-patching mail list?
The code was based Linus' tree, probably 5.19-rc7.
>
> Second, I rebased the klp-convert-tree on top of v5.19 here:
> https://github.com/joe-lawrence/klp-convert-tree/tree/klp-convert-v7-devel
>
> and I can confirm that at least the x86_64 livepatching selftests
> (including the klp-relocation tests added by this tree) do pass. I
> haven't had a chance to try writing new tests to verify this specific
> patch, but I'll take a look next week.
I also got the selftests pass for another patch. Checking dmesg is
a little tricky, btw. I will take a look at klp-convert.
Thanks,
Song
