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

[Tao Liu]

Hi Baoquan,

On Fri, Jun 26, 2026 at 8:38 PM Tao Liu <ltao@xxxxxxxxxx> wrote:
>
> Hi Baoquan,
>
> Glad to see your message again!
>
> Thanks for the Ack and the suggestion for the comment, I will add it
> in the next version.
>
> In the meantime, I will check if similar issue exists on LoongArch as well.
>
> Thanks,
> Tao Liu
>
> On Fri, Jun 26, 2026 at 8:04 PM Baoquan He <bhe@xxxxxxxxxx> wrote:
> >
> > Add kexec ML to CC.
> >
> > On Fri, Jun 26, 2026 at 7:46 AM Tao Liu <ltao@xxxxxxxxxx> wrote:
> > >
> > > Kindly ping, any comments?
> > >
> > > Thanks,
> > > Tao Liu
> > >
> > > On Fri, May 29, 2026 at 3:35 PM Tao Liu <ltao@xxxxxxxxxx> 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 <ltao@xxxxxxxxxx>
> > > > ---
> > > >  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?

I have tested in LoongArch, it doesn't have the similar issue. The
reason is, in arch/loongarch/kernel/machine_kexec.c:machine_kexec_prepare(),
the unchecked memcpy() only happens for none kexec file load, however
ima_add_kexec_buffer() requires kexec file load. So the condition
isn't met.

> >
> > Other than above concerns, this patch looks good to me:
> >
> > Acked-by: Baoquan He <bhe@xxxxxxxxxx>

Thanks for your code review and suggestions!

Thanks,
Tao Liu

> >
> > > >                 if (image->file_mode)
> > > >                         memcpy(&fdt, image->segment[i].buf, sizeof(fdt));
> > > >                 else if (copy_from_user(&fdt, image->segment[i].buf, sizeof(fdt)))
> > > > --
> > > > 2.47.0
> > > >
> > >
> > >
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> > > linux-riscv@xxxxxxxxxxxxxxxxxxx
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> > >
> >