netdev - Re: [PATCH 1/9] kernel: add a PF_FORCE

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Message-ID: <20200918135822.GZ3421308@ZenIV.linux.org.uk>
Date:   Fri, 18 Sep 2020 14:58:22 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Christoph Hellwig <hch@....de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>, Arnd Bergmann <arnd@...db.de>,
        David Howells <dhowells@...hat.com>,
        linux-arm-kernel@...ts.infradead.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-block@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-aio@...ck.org,
        io-uring@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, netdev@...r.kernel.org,
        keyrings@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag

On Fri, Sep 18, 2020 at 03:44:06PM +0200, Christoph Hellwig wrote:
> On Fri, Sep 18, 2020 at 02:40:12PM +0100, Al Viro wrote:
> > >  	/* Vector 0x110 is LINUX_32BIT_SYSCALL_TRAP */
> > > -	return pt_regs_trap_type(current_pt_regs()) == 0x110;
> > > +	return pt_regs_trap_type(current_pt_regs()) == 0x110 ||
> > > +		(current->flags & PF_FORCE_COMPAT);
> > 
> > Can't say I like that approach ;-/  Reasoning about the behaviour is much
> > harder when it's controlled like that - witness set_fs() shite...
> 
> I don't particularly like it either.  But do you have a better idea
> how to deal with io_uring vs compat tasks?

<wry> git rm fs/io_uring.c would make a good starting point </wry>
Yes, I know it's not going to happen, but one can dream...

Said that, why not provide a variant that would take an explicit
"is it compat" argument and use it there?  And have the normal
one pass in_compat_syscall() to that...