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From:   Andy Lutomirski <luto@amacapital.net>
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Date:   Thu, 28 Nov 2019 13:13:34 -0800
Message-Id: <EB7AF2AE-6CA3-4395-AA37-BF92EE308A42@amacapital.net>
Subject: Re: [PATCH] ptrace/x86: introduce TS_COMPAT_RESTART to fix get_nr_restart_syscall()
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To:     Linus Torvalds <torvalds@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>
Cc:     Oleg Nesterov <oleg@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@kernel.org>,
        Jan Kratochvil <jan.kratochvil@redhat.com>,
        Pedro Alves <palves@redhat.com>, Peter Anvin <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>
Sender: linux-kernel-owner@vger.kernel.org
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>> On Nov 28, 2019, at 11:25 AM, Linus Torvalds <torvalds@linux-foundation.o=
rg> wrote:
>>=20
>> =EF=BB=BFOn Thu, Nov 28, 2019 at 7:36 AM Oleg Nesterov <oleg@redhat.com> w=
rote:
>> You misunderstood my question, I do not see a good place for the code
>> above. So I am going to uglify */signal.[ch] files.
>=20
> Ahh, ok, I thought that was kind of understood.
>=20
>> --- a/arch/x86/include/asm/signal.h
>> +++ b/arch/x86/include/asm/signal.h
>> @@ -5,6 +5,10 @@
>> #ifndef __ASSEMBLY__
>> #include <linux/linkage.h>
>> +struct restart_block;
>> +extern void arch_set_restart_data(struct restart_block *);
>> +#define arch_set_restart_data  arch_set_restart_data
>=20
> I'd just replace this with
>=20
>  /* We need to save TS_COMPAT at the time of the call */
>  #define arch_set_restart_data(blk) (blk)->arch_data =3D
> current_thread_info()->status
>=20
> or something like that.

I think this doesn=E2=80=99t work for x32. Let=E2=80=99s either save the res=
ult of syscall_get_arch() or just actually calculate and save the restart_sy=
scall nr here.

Before we commit to this, Kees, do you think we can manage to just renumber r=
estart_syscall()?  That=E2=80=99s a much better solution if we can pull it o=
ff.

>=20
>              Linus