Re: [PATCH] livepatch: x86: bugfix about kASLR

[zhouchengming]

On 2015/11/4 17:44, Jiri Kosina wrote:
> On Wed, 4 Nov 2015, Zhou Chengming wrote:
>
> > When enable KASLR, func->old_addr will be set to zero
> > and livepatch will find the right old address.
> > But for reloc, livepatch just verify it using reloc->val
> > (old addr from user), so verify failed and report
> > "kernel mismatch" error.
> >
> > Reported-by: Cyril B.<cbay@xxxxxxxxxxxxxx>
> > Signed-off-by: Zhou Chengming<zhouchengming1@xxxxxxxxxx>
> > ---
> >   kernel/livepatch/core.c |    7 ++++++-
> >   1 files changed, 6 insertions(+), 1 deletions(-)
> >
> > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> > index 53196e2..c8885c6 100644
> > --- a/kernel/livepatch/core.c
> > +++ b/kernel/livepatch/core.c
> > @@ -311,7 +311,12 @@ static int klp_write_object_relocations(struct module *pmod,
> >   		return -EINVAL;
> >
> >   	for (reloc = obj->relocs; reloc->name; reloc++) {
> > -		if (!klp_is_module(obj)) {
> > +
> > +#if defined(CONFIG_RANDOMIZE_BASE)
> CONFIG_RANDOMIZE_BASE being enabled by itself doesn't directly imply that
> kASLR has been actually really enabled during runtime. You need
> to check kaslr_enabled() as well.

Right.

> > +		/* KASLR is enabled, disregard old_addr from user */
> > +		reloc->val = 0;
> Is there a reason why to discard it completely? Adding kaslr_offset()
> should give us the correct address, right?
>
> Thanks,

Yes, it's definitely better.

Thanks


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