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Date: Fri, 15 Jan 2021 16:07:46 -0800 From: Andy Lutomirski <luto@...nel.org> To: Arnd Bergmann <arnd@...nel.org>, Christoph Hellwig <hch@....de> Cc: Ryan Houdek <sonicadvance1@...il.com>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Alexander Viro <viro@...iv.linux.org.uk>, Arnd Bergmann <arnd@...db.de>, Christian Brauner <christian.brauner@...ntu.com>, Andrew Morton <akpm@...ux-foundation.org>, Minchan Kim <minchan@...nel.org>, Aleksa Sarai <cyphar@...har.com>, Sargun Dhillon <sargun@...gun.me>, Miklos Szeredi <mszeredi@...hat.com>, Vincenzo Frascino <vincenzo.frascino@....com>, "Amanieu d'Antras" <amanieu@...il.com>, Willem de Bruijn <willemb@...gle.com>, YueHaibing <yuehaibing@...wei.com>, Xiaoming Ni <nixiaoming@...wei.com>, Heiko Carstens <hca@...ux.ibm.com>, "Eric W. Biederman" <ebiederm@...ssion.com>, Joe Perches <joe@...ches.com>, Jan Kara <jack@...e.cz>, David Rientjes <rientjes@...gle.com>, Arnaldo Carvalho de Melo <acme@...hat.com>, "David S. Miller" <davem@...emloft.net>, Linux ARM <linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>, Linux API <linux-api@...r.kernel.org>, linux-arch <linux-arch@...r.kernel.org> Subject: Re: [PATCH] Adds a new ioctl32 syscall for backwards compatibility layers On Fri, Jan 15, 2021 at 1:03 AM Arnd Bergmann <arnd@...nel.org> wrote: > > On Fri, Jan 15, 2021 at 3:06 AM Ryan Houdek <sonicadvance1@...il.com> wrote: > > On Wed, Jan 6, 2021 at 12:49 AM Arnd Bergmann <arnd@...nel.org> wrote: > >> On Wed, Jan 6, 2021 at 7:48 AM <sonicadvance1@...il.com> wrote: > >> > From: Ryan Houdek <Sonicadvance1@...il.com> > >> ... > >> > >> For x86, this has another complication, as some ioctls also need to > >> check whether they are in an ia32 task (with packed u64 and 32-bit > >> __kernel_old_time_t) or an x32 task (with aligned u64 and 64-bit > >> __kernel_old_time_t). If the new syscall gets wired up on x86 as well, > >> you'd need to decide which of the two behaviors you want. > > > > > > I can have a follow-up patch that makes this do ni-syscall on x86_64 since > > we can go through the int 0x80 handler, or x32 handler path and choose > > whichever one there. > > I'd say for consistency > We need to make it crystal clear on x86 what this ioctl does. We have a silly selection of options: - ioctl32() via SYSCALL, x32 bit clear -- presumably does an i386 ioctl? - ioctl32() via SYSCALL, x32 bit set -- this needs to do something clearly documented. - ioctl32() via int80 -- presumably you're not wiring this up In any case, the compat alloc thing should just go away. It's a hack and serves no real purpose. Finally, I'm not convinced that this patch works correctly. We have in_compat_syscall(), and code that uses it may well be reachable from ioctl. I personally would like to see in_compat_syscall() go away, but some other people (Hi, Christoph!) disagree, and usage seems to be increasing, not decreasing.
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