linux-kernel - Re: [RESEND][PATCH v2 1/3] syscalls,x86 Expose arch

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Date:   Thu, 15 Sep 2016 01:29:53 +0300
From:   Dmitry Safonov <0x7f454c46@...il.com>
To:     Kyle Huey <me@...ehuey.com>
Cc:     "Robert O'Callahan" <robert@...llahan.org>,
        open list <linux-kernel@...r.kernel.org>,
        Borislav Petkov <bp@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Milosz Tanski <milosz@...in.com>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        David Howells <dhowells@...hat.com>,
        Zach Brown <zab@...hat.com>,
        Eric B Munson <emunson@...mai.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Slaby <jslaby@...e.cz>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Borislav Petkov <bp@...en8.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        Mateusz Guzik <mguzik@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [RESEND][PATCH v2 1/3] syscalls,x86 Expose arch_prctl on x86-32.

2016-09-15 1:08 GMT+03:00 Kyle Huey <me@...ehuey.com>:
> On Wed, Sep 14, 2016 at 2:59 PM, Dmitry Safonov <0x7f454c46@...il.com> wrote:
>> 2016-09-15 0:08 GMT+03:00 Kyle Huey <me@...ehuey.com>:
>>> Signed-off-by: Kyle Huey <khuey@...ehuey.com>
>>> ---
>>>  arch/x86/entry/syscalls/syscall_32.tbl |  1 +
>>>  arch/x86/kernel/process.c              | 80 ++++++++++++++++++++++++++++++++++
>>>  arch/x86/kernel/process_64.c           | 66 ----------------------------
>>>  3 files changed, 81 insertions(+), 66 deletions(-)
>>>
>>> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
>>> index f848572..3b6965b 100644
>>> --- a/arch/x86/entry/syscalls/syscall_32.tbl
>>> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
>>> @@ -386,3 +386,4 @@
>>>  377    i386    copy_file_range         sys_copy_file_range
>>>  378    i386    preadv2                 sys_preadv2                     compat_sys_preadv2
>>>  379    i386    pwritev2                sys_pwritev2                    compat_sys_pwritev2
>>> +380    i386    arch_prctl              sys_arch_prctl
>>
>> Why not define it as other 32-bit syscalls with compat_sys_ prefix
>> with the help of COMPAT_SYSCALL_DEFINE() macro?
>> Then you could omit code moving, drop is_32 helper.
>> I miss something obvious?
>
> The code will have to move regardless, because right now do_arch_prctl
> is in process-64.c which is only compiled on a 64 bit kernel.

Why? This code will not work anyway for 32-bit in your patches
by obscuring it with is_32.

> As I told Dave Hansen in the non-RESEND thread (not sure why
> git-send-email didn't put him in this one ...) I considered doing a
> compat_sys_arch_prctl that would reject the relevant arch_prctls that
> don't apply on 32 bit but I didn't see any prior art for it (in my
> admittedly non-exhaustive search).

Well, you could just add to 64-bit do_arch_prctl() new cases for your
prctls - that would be just a two-lines for each new prctl.
Also add compat_sys_ and define *only* what's needed there for you,
do not add there ARCH_{SET,GET}_{FS,GS}.
Does this make sense?

-- 
             Dmitry