linux-kernel - Re: ia32 signed long treated as x64 unsigned int by __ia32

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Date:   Thu, 23 Sep 2021 11:01:09 +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: ia32 signed long treated as x64 unsigned int by __ia32_sys*

Hello Arnd,

Arnd Bergmann <arnd@...db.de> writes:

> On Wed, Sep 22, 2021 at 10:46 AM Richard Palethorpe <rpalethorpe@...e.de> wrote:
>> Richard Palethorpe <rpalethorpe@...e.de> writes:
>
>> >
>> > 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
>>
>> and below is the macro expansion for the automatically generated 32bit to
>> 64bit io_pgetevents. I believe it is casting u32 to s64, which appears
>> to mean there is no sign extension. I don't know if this is the expected
>> behaviour?
>
> Thank you for digging through this, I meant to already reply once more yesterday
> but didn't get around to that.

Thanks, no problem. I suppose this will effect other systemcalls as
well. Which if nothing else is a pain for testing.

>
>>     __typeof(__builtin_choose_expr(
>>         (__builtin_types_compatible_p(typeof((long)0), typeof(0LL)) ||
>>          __builtin_types_compatible_p(typeof((long)0), typeof(0ULL))),
>>         0LL, 0L)) min_nr,
>>     __typeof(__builtin_choose_expr(
>>         (__builtin_types_compatible_p(typeof((long)0), typeof(0LL)) ||
>>          __builtin_types_compatible_p(typeof((long)0), typeof(0ULL))),
>>         0LL, 0L)) nr,
>
> The part that I remembered is in arch/s390/include/asm/syscall_wrapper.h,
> which uses this version instead:
>
> #define __SC_COMPAT_CAST(t, a)                                          \
> ({                                                                      \
>         long __ReS = a;                                                 \
>                                                                         \
>         BUILD_BUG_ON((sizeof(t) > 4) && !__TYPE_IS_L(t) &&              \
>                      !__TYPE_IS_UL(t) && !__TYPE_IS_PTR(t) &&           \
>                      !__TYPE_IS_LL(t));                                 \
>         if (__TYPE_IS_L(t))                                             \
>                 __ReS = (s32)a;                                         \
>         if (__TYPE_IS_UL(t))                                            \
>                 __ReS = (u32)a;                                         \
>         if (__TYPE_IS_PTR(t))                                           \
>                 __ReS = a & 0x7fffffff;                                 \
>         if (__TYPE_IS_LL(t))                                            \
>                 return -ENOSYS;                                         \
>         (t)__ReS;                                                       \
> })
>
> This also takes care of s390-specific pointer conversion, which is the
> reason for needing an architecture-specific wrapper, but I suppose the
> handling of signed arguments as done in s390 should also be done
> everywhere else.
>
> I also noticed that only x86 and s390 even have separate entry
> points for normal syscalls when called in compat mode, while
> the others all just zero the upper halves of the registers in the
> low-level entry code and then call the native entry point.
>
>         Arnd

It looks to me like aarch64 also has something similar? At any rate, I
can try to fix it for x86 and investigate what else might be effected.

-- 
Thank you,
Richard.