Re: [PATCH] riscv: Fix a NULL pointer reference in machine_kexec_prepare

[Tao Liu]

Hi Pratyush,

On Mon, Jun 29, 2026 at 11:13 PM Pratyush Yadav <praty...@kernel.org> wrote:
>
> +Cc IMA maintainers
>
> On Fri, Jun 26 2026, Baoquan He wrote:
>
> > Add kexec ML to CC.
> >
> > On Fri, Jun 26, 2026 at 7:46 AM Tao Liu <l...@redhat.com> wrote:
> >>
> >> Kindly ping, any comments?
> >>
> >> Thanks,
> >> Tao Liu
> >>
> >> On Fri, May 29, 2026 at 3:35 PM Tao Liu <l...@redhat.com> wrote:
> >> >
> >> > A NULL pointer reference issue is noticed in riscv's 
> >> > machine_kexec_prepare,
> >> > where image->segment[i].buf might be NULL and copied unchecked.
> >> >
> >> > The NULL buf comes from security/integrity/ima/ima_kexec.c:
> >> > ima_add_kexec_buffer(), where kbuf is added by kexec_add_buffer(),
> >> > but kbuf.buffer is NULL.
> >> >
> >> > Fix this by simply adding a check before copy.
> >> >
> >> > Signed-off-by: Tao Liu <l...@redhat.com>
> >> > ---
> >> >  arch/riscv/kernel/machine_kexec.c | 3 +++
> >> >  1 file changed, 3 insertions(+)
> >> >
> >> > diff --git a/arch/riscv/kernel/machine_kexec.c 
> >> > b/arch/riscv/kernel/machine_kexec.c
> >> > index 2306ce3e5f22..d81d576f9cb5 100644
> >> > --- a/arch/riscv/kernel/machine_kexec.c
> >> > +++ b/arch/riscv/kernel/machine_kexec.c
> >> > @@ -41,6 +41,9 @@ machine_kexec_prepare(struct kimage *image)
> >> >                 if (image->segment[i].memsz <= sizeof(fdt))
> >> >                         continue;
> >> >
> >> > +               if (image->segment[i].buf == NULL)
> >> > +                       continue;
> >> > +
> >
> > This is a good fix, maybe we can add code comments to explain it as
> > below, just for reference.
> >
> >                /*
> >                 * Some segments (e.g. IMA) reserve space but have no buffer
> >                 * loaded yet. Skip them as they cannot contain an FDT.
> >                 */
> > And is there any other place where the similar issue exists? e.g on 
> > LoongArch?
> >
> > Other than above concerns, this patch looks good to me:
> >
> > Acked-by: Baoquan He <b...@redhat.com>
>
> Yeah, the patch LGTM to me too.
>
> Acked-by: Pratyush Yadav <praty...@kernel.org>
>
> Although I think IMA can make this a bit easier to understand. First, in
> ima_add_kexec_buffer() it should set kbuf.buffer to NULL and kbuf.bufsz
> to 0 explicitly instead of using kexec_buffer and kexec_buffer_size
> which are initialized to NULL and 0, but never updated. Using the
> variables here adds an extra level of indirection.
>
> Also, perhaps we should add a comment in ima_add_kexec_buffer() about
> how this all works, since where the IMA buffer lives and where it gets
> updated it fairly complicated and took me some time to piece together.

Thanks for your patch review and suggestions! I agree with your point
on the IMA part, I was confused by the code too, e.g in
ima_add_kexec_buffer():

void *kexec_buffer = NULL;
kbuf.buffer = kexec_buffer;
ret = kexec_add_buffer(&kbuf);
if (ret) {
    pr_err("Error passing over kexec measurement buffer.\n");
    vfree(kexec_buffer);
    return;
}

Do we need to vfree(kexec_buffer)? When kexec_buffer is NULL and seems
never get updated.

I'm not familiar with IMA code, maybe there is a reason which I'm unaware of...

Thanks,
Tao Liu



>
> --
> Regards,
> Pratyush Yadav
>