linux-kernel - Re: [PATCH v5 4/6] mm: simplify compat numa syscalls

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Message-ID: <CAK8P3a3itgCyc4jDBodTOcwG+XXsDYspZqQVBmy88cGXevY5Yw@mail.gmail.com>
Date:   Tue, 27 Jul 2021 19:40:05 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Christoph Hellwig <hch@...radead.org>,
        Feng Tang <feng.tang@...el.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        Parisc List <linux-parisc@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        sparclinux <sparclinux@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v5 4/6] mm: simplify compat numa syscalls

On Tue, Jul 27, 2021 at 7:27 PM Heiko Carstens <hca@...ux.ibm.com> wrote:
>
> On Tue, Jul 27, 2021 at 04:48:57PM +0200, Arnd Bergmann wrote:
> > ---
> >  include/linux/compat.h |  17 ++--
> >  mm/mempolicy.c         | 175 +++++++++++++----------------------------
> >  2 files changed, 63 insertions(+), 129 deletions(-)
> ...
> > +static int get_bitmap(unsigned long *mask, const unsigned long __user *nmask,
> > +                   unsigned long maxnode)
> > +{
> > +     unsigned long nlongs = BITS_TO_LONGS(maxnode);
> > +     int ret;
> > +
> > +     if (in_compat_syscall())
> > +             ret = compat_get_bitmap(mask,
> > +                                     (const compat_ulong_t __user *)nmask,
> > +                                     maxnode);
>
> compat_ptr() conversion for e.g. nmask is missing with the next patch
> which removes the compat system calls.
> Is that intended or am I missing something?

I don't think it's needed here, since the pointer comes from the system
call argument, which has the compat_ptr() conversion applied in
arch/s390/include/asm/syscall_wrapper.h, not from a compat_uptr_t
that gets passed indirectly. The compat_get_bitmap() conversion
is only needed for byte order adjustment, not for converting pointers.

It's also possible that I'm the one who's missing something.

        Arnd