Re: [PATCH] ppc/spapr: Fix ubsan warning with unaligned pointer access

[Alexey Kardashevskiy]

On 20/12/2023 12:45, Richard Henderson wrote:
> On 12/16/23 16:14, Daniel Hoffman wrote:
> > Found while running QTest with UBsan. Unaligned pointers appear to be
> > valid, so moving the read to an explicit memcpy to an intermediate.
> > ---
> >   hw/ppc/vof.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/ppc/vof.c b/hw/ppc/vof.c
> > index e3b430a81f4..609a51c645d 100644
> > --- a/hw/ppc/vof.c
> > +++ b/hw/ppc/vof.c
> > @@ -646,7 +646,10 @@ static void vof_dt_memory_available(void *fdt, 
> > GArray *claimed, uint64_t base)
> >       mem0_reg = fdt_getprop(fdt, offset, "reg", &proplen);
> >       g_assert(mem0_reg && proplen == sizeof(uint32_t) * (ac + sc));
> >       if (sc == 2) {
> > -        mem0_end = be64_to_cpu(*(uint64_t *)(mem0_reg + 
> > sizeof(uint32_t) * ac));
> > +        /* Pointer may be unaligned */
> > +        uint64_t mem0_end_copy;
> > +        memcpy(&mem0_end_copy, mem0_reg + sizeof(uint32_t) * ac, 
> > sizeof(mem0_end_copy));
> > +        mem0_end = be64_to_cpu(mem0_end_copy);
>
> mem0_end = ldq_be_p(mem0_reg + sizeof(uint32_t) * ac);


+1 for ldq_be_p(). Or read lo&hi 32bit chunks and combine. Thanks,

> r~

--
Alexey