Re: [PATCH 07/14] target/s390x: Fix assertion failure in VFMIN/VFMAX with reserved type

[Ilya Leoshkevich <iii@linux.ibm.com>]

On Wed, 2023-07-19 at 10:40 +0200, David Hildenbrand wrote:
> On 18.07.23 23:21, Ilya Leoshkevich wrote:
> > Passing reserved type to VFMIN/VFMAX causes an assertion failure in
> > vfmin_res() and vfmax_res(). These instructions should raise a
> > specification exception in this case.
> > 
> > Cc: qemu-stable@nongnu.org
> > Fixes: da4807527f3b ("s390x/tcg: Implement VECTOR FP
> > (MAXIMUM|MINIMUM)")
> > Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> > ---
> >   target/s390x/tcg/vec_fpu_helper.c | 24 +++++++++++++++---------
> >   1 file changed, 15 insertions(+), 9 deletions(-)
> > 
> > diff --git a/target/s390x/tcg/vec_fpu_helper.c
> > b/target/s390x/tcg/vec_fpu_helper.c
> > index 75cf605b9f4..f1671679879 100644
> > --- a/target/s390x/tcg/vec_fpu_helper.c
> > +++ b/target/s390x/tcg/vec_fpu_helper.c
> > @@ -915,7 +915,7 @@ static void vfminmax32(S390Vector *v1, const
> > S390Vector *v2,
> >           float32 b = s390_vec_read_float32(v3, i);
> >           float32 result;
> >   
> 
> Why not check for invalid types once first and leave the rest of that
> function alone?
> 
> diff --git a/target/s390x/tcg/vec_fpu_helper.c
> b/target/s390x/tcg/vec_fpu_helper.c
> index 75cf605b9f..e0b2a78632 100644
> --- a/target/s390x/tcg/vec_fpu_helper.c
> +++ b/target/s390x/tcg/vec_fpu_helper.c
> @@ -910,6 +910,11 @@ static void vfminmax32(S390Vector *v1, const
> S390Vector *v2,
>       S390Vector tmp = {};
>       int i;
>   
> +    if (type > S390_MINMAX_TYPE_F) {
> +        tcg_s390_program_interrupt(env, PGM_SPECIFICATION, retaddr);
> +    }
> +
>       for (i = 0; i < 4; i++) {
>           float32 a = s390_vec_read_float32(v2, i);
>           float32 b = s390_vec_read_float32(v3, i);
> 

I have taken another look, and turns out there already is:

static DisasJumpType op_vfmax(DisasContext *s, DisasOps *o)
{
    ...

    if (m6 == 5 || m6 == 6 || m6 == 7 || m6 > 13) {
        gen_program_exception(s, PGM_SPECIFICATION);
        return DISAS_NORETURN;
    }

What the fuzzer has found was the m6 == 13 case, so only a small
adjustment is needed.