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

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Message-ID: <87lf3qkk72.fsf@suse.de>
Date:   Tue, 21 Sep 2021 16:44:01 +0100
From:   Richard Palethorpe <rpalethorpe@...e.de>
To:     Arnd Bergmann <arnd@...db.de>
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>,
        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


Richard Palethorpe <rpalethorpe@...e.de> writes:

> Hello Arnd,
>
> Arnd Bergmann <arnd@...db.de> writes:
>
>> 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.
>
> That is what I thought, but I couldn't think of another explanation for
> it.
>
>>
>> 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
>
> No, but I suppose I can try it on ARM or PowerPC. I suppose printing the
> arguments would be a good idea too.

It appears it really is failing to sign extend the s32 to s64. I added
the following printks

modified   fs/aio.c
@@ -2054,6 +2054,7 @@ static long do_io_getevents(aio_context_t ctx_id,
 	long ret = -EINVAL;
 
 	if (likely(ioctx)) {
+		printk("comparing %ld <= %ld\n", min_nr, nr);
 		if (likely(min_nr <= nr && min_nr >= 0))
 			ret = read_events(ioctx, min_nr, nr, events, until);
 		percpu_ref_put(&ioctx->users);
@@ -2114,6 +2115,8 @@ SYSCALL_DEFINE6(io_pgetevents,
 	bool interrupted;
 	int ret;
 
+	printk("io_pgetevents(%lx, %ld, %ld, ...)\n", ctx_id, min_nr, nr);
+
 	if (timeout && unlikely(get_timespec64(&ts, timeout)))
 		return -EFAULT;

Then the output is:

[   11.252268] io_pgetevents(f7f19000, 4294967295, 1, ...)
[   11.252401] comparing 4294967295 <= 1
io_pgetevents02.c:114: TPASS: invalid min_nr: io_pgetevents() failed as expected: EINVAL (22)
[   11.252610] io_pgetevents(f7f19000, 1, 4294967295, ...)
[   11.252748] comparing 1 <= 4294967295
io_pgetevents02.c:103: TFAIL: invalid max_nr: io_pgetevents() passed unexpectedly

-- 
Thank you,
Richard.