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

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Message-ID: <YQBSpxZR4P/Phpf1@osiris>
Date:   Tue, 27 Jul 2021 20:38:31 +0200
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Arnd Bergmann <arnd@...nel.org>
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 07:40:05PM +0200, Arnd Bergmann wrote:
> On Tue, Jul 27, 2021 at 7:27 PM Heiko Carstens <hca@...ux.ibm.com> wrote:
> > > +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.

What I was trying to say: this patch on its own is ok. However with
the next patch you remove the compat system calls and map the regular
system calls instead.

That is:

-COMPAT_SYSCALL_DEFINE6(mbind, compat_ulong_t, start, compat_ulong_t, len,
-		       compat_ulong_t, mode, compat_ulong_t __user *, nmask,
-		       compat_ulong_t, maxnode, compat_ulong_t, flags)
-{
-	return kernel_mbind(start, len, mode, (unsigned long __user *)nmask,
-			    maxnode, flags);
-}

and this:

-268  common	mbind			sys_mbind			compat_sys_mbind
-269  common	get_mempolicy		sys_get_mempolicy		compat_sys_get_mempolicy
-270  common	set_mempolicy		sys_set_mempolicy		compat_sys_set_mempolicy
+268  common	mbind			sys_mbind			sys_mbind
+269  common	get_mempolicy		sys_get_mempolicy		sys_get_mempolicy
+270  common	set_mempolicy		sys_set_mempolicy		sys_set_mempolicy

would remove compat_ptr() conversion from nmask above if I'm not mistaken.