linux-kernel - Re: [PATCH] ptrace/x86: introduce TS_COMPAT_RESTART to fix get_nr_restart

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Date:   Thu, 28 Nov 2019 13:13:34 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
        Jan Kratochvil <jan.kratochvil@...hat.com>,
        Pedro Alves <palves@...hat.com>, Peter Anvin <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH] ptrace/x86: introduce TS_COMPAT_RESTART to fix get_nr_restart_syscall()



>> On Nov 28, 2019, at 11:25 AM, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>> 
>> On Thu, Nov 28, 2019 at 7:36 AM Oleg Nesterov <oleg@...hat.com> wrote:
>> You misunderstood my question, I do not see a good place for the code
>> above. So I am going to uglify */signal.[ch] files.
> 
> Ahh, ok, I thought that was kind of understood.
> 
>> --- 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
> 
> I'd just replace this with
> 
>  /* We need to save TS_COMPAT at the time of the call */
>  #define arch_set_restart_data(blk) (blk)->arch_data =
> current_thread_info()->status
> 
> or something like that.

I think this doesn’t work for x32. Let’s either save the result of syscall_get_arch() or just actually calculate and save the restart_syscall nr here.

Before we commit to this, Kees, do you think we can manage to just renumber restart_syscall()?  That’s a much better solution if we can pull it off.

> 
>              Linus