Re: [PATCH] parisc: Increase the usage check of kmalloc allocated object a

[Helge Deller]

On 9/14/22 08:43, Rolf Eike Beer wrote:
> Am Mittwoch, 14. September 2022, 08:18:19 CEST schrieb Helge Deller:
> > On 9/14/22 08:04, Li zeming wrote:
> > > In the case of memory allocation failure, no alignment operation is
> > > required.
> > >
> > > Signed-off-by: Li zeming <zeming@xxxxxxxxxxxx>
> > > ---
> > >
> > >    drivers/parisc/iosapic.c | 4 +++-
> > >    1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/parisc/iosapic.c b/drivers/parisc/iosapic.c
> > > index 3a8c98615634..33de438916d3 100644
> > > --- a/drivers/parisc/iosapic.c
> > > +++ b/drivers/parisc/iosapic.c
> > > @@ -229,7 +229,9 @@ static struct irt_entry *iosapic_alloc_irt(int
> > > num_entries)>
> > >    	 * 4-byte alignment on 32-bit kernels
> > >    	 */
> > >
> > >    	a = (unsigned long)kmalloc(sizeof(struct irt_entry) * num_entries
> + 8,
> > >    	GFP_KERNEL);>
> > > -	a = (a + 7UL) & ~7UL;
> > > +	if (a)
> > > +		a = (a + 7UL) & ~7UL;
> > > +
> >
> > As you said, the adjustment isn't required, but it's still ok.
> > So I think the additional "if" isn't necessary and so I'm not
> > applying your patch.
> >
> > Anyway, thanks for your help to try to improve the code!
>
> I was about to say the same, but from looking at the code I don't think what
> is in there is correct either. The comment seems outdated, because
> __assume_kmalloc_alignment, which is __alignof__(unsigned long long). This
> code is untouched for the entire git history, so maybe we can just change the
> whole thing to
>
>    return kcalloc(num_entries, sizeof(struct irt_entry))
>
> now?

Yes, your proposal is good.
Anyone want to send a patch (with a small comment that kcalloc() will return
at least the required 8-byte alignment)?

> And these functions end up propagating an allocation error in this file and it
> will never reach kernel/setup.c, which seems bad.

That part I don't understand.
The return value of iosapic_alloc_irt() is checked afterwards, but you probably
meant something else?

> But I guess the only point where this really can go wrong if the PDC
> returns an absurdly large number of entries.
Helge