Re: [PATCH 1/3] target/ppc/kvm: Replace variable length array in kvmppc_save_htab()

[Thomas Huth]

On 21/02/2024 17.29, Peter Maydell wrote:
> On Wed, 21 Feb 2024 at 16:26, Thomas Huth <thuth@redhat.com> wrote:
> > To be able to compile QEMU with -Wvla (to prevent potential security
> > issues), we need to get rid of the variable length array in the
> > kvmppc_save_htab() function. Replace it with a heap allocation instead.
> >
> > Signed-off-by: Thomas Huth <thuth@redhat.com>
> > ---
> >   target/ppc/kvm.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> > index 26fa9d0575..e7e39c3091 100644
> > --- a/target/ppc/kvm.c
> > +++ b/target/ppc/kvm.c
> > @@ -2688,7 +2688,7 @@ int kvmppc_get_htab_fd(bool write, uint64_t index, Error 
> > **errp)
> >   int kvmppc_save_htab(QEMUFile *f, int fd, size_t bufsize, int64_t max_ns)
> >   {
> >       int64_t starttime = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
> > -    uint8_t buf[bufsize];
> > +    g_autofree uint8_t *buf = g_malloc(bufsize);
> >       ssize_t rc;
>
> This works, so
> Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
>
> but you could also drop the bufsize argument, because there are only
> two callers and they both pass MAX_KVM_BUF_SIZE, and then declare the
> array as fixed size with "uint8_t buf[MAX_KVM_BUF_SIZE]".

Yes, that's an alternative ... my thinking was that MAX_KVM_BUF_SIZE = 2048 
is already a rather big buffer which should maybe rather be allocated on the 
heap than the stack? But I don't mind too much, so if ppc folks prefer the 
stack allocation, I can change the patch, too.

 Thomas