linux-kernel - Re: [PATCH] aio: Wire up compat_sys_io_pgetevents

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Date:   Tue, 21 Sep 2021 15:32:53 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Richard Palethorpe <rpalethorpe@...e.com>
Cc:     Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        linux-aio <linux-aio@...ck.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Andy Lutomirski <luto@...nel.org>,
        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>, Arnd Bergmann <arnd@...db.de>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        LTP List <ltp@...ts.linux.it>
Subject: Re: [PATCH] aio: Wire up compat_sys_io_pgetevents_time64 for x86

On Tue, Sep 21, 2021 at 3:01 PM Richard Palethorpe <rpalethorpe@...e.com> wrote:
>
> The LTP test io_pgetevents02 fails in 32bit compat mode because an
> nr_max of -1 appears to be treated as a large positive integer. This
> causes pgetevents_time64 to return an event. The test expects the call
> to fail and errno to be set to EINVAL.
>
> Using the compat syscall fixes the issue.
>
> Fixes: 7a35397f8c06 ("io_pgetevents: use __kernel_timespec")
> Signed-off-by: Richard Palethorpe <rpalethorpe@...e.com>

Thanks a lot for finding this, indeed there is definitely a mistake that
this function is defined and not used, but I don't yet see how it would
get to the specific failure you report.

Between the two implementations, I can see a difference in the
handling of the signal mask, but that should only affect architectures
with incompatible compat_sigset_t, i.e. big-endian or
_COMPAT_NSIG_WORDS!=_NSIG_WORDS, and the latter is
never true for currently supported architectures. On x86, there is
no difference in the sigset at all.

The negative 'nr' and 'min_nr' arguments that you list as causing
the problem /should/ be converted by the magic
SYSCALL_DEFINE6() definition. If this is currently broken, I would
expect other syscalls to be affected as well.

Have you tried reproducing this on non-x86 architectures? If I
misremembered how the compat conversion in SYSCALL_DEFINE6()
works, then all architectures that support CONFIG_COMPAT have
to be fixed.

         Arnd