linux-kernel - Re: [RFC PATCH v2] ptrace: add PTRACE_GET_SYSCALL

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Date:   Wed, 21 Nov 2018 14:56:57 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Elvira Khabirova <lineprinter@...linux.org>,
        Kees Cook <keescook@...omium.org>,
        Sasha Levin <sasha.levin@...cle.com>,
        Linux API <linux-api@...r.kernel.org>,
        Jann Horn <jannh@...gle.com>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Andrew Lutomirski <luto@...nel.org>,
        strace-devel@...ts.strace.io
Subject: Re: [RFC PATCH v2] ptrace: add PTRACE_GET_SYSCALL_INFO request

Please cc linux-api@...r.kernel.org for future versions.

On Wed, Nov 21, 2018 at 7:58 AM Elvira Khabirova
<lineprinter@...linux.org> wrote:
>
> struct ptrace_syscall_info {
>         __u8 op; /* 0 for entry, 1 for exit */

Can you add proper defines, like:

#define PTRACE_SYSCALL_ENTRY 0
#define PTRACE_SYSCALL_EXIT 1
#define PTRACE_SYSCALL_SECCOMP 2

and make seccomp work from the start?  I'd rather we don't merge an
implementation that doesn't work for seccomp and then have to rework
it later.

>         __u8 __pad0[7];
>         union {
>                 struct {
>                         __s32 nr;

__u64 please.  Syscall numbers are, as a practical matter, 64 bits.
Admittedly, the actual effects of setting the high bits are unclear,
and seccomp has issues with it, but let's not perpetuate the problem.

>                         __u32 arch;
>                         __u64 instruction_pointer;
>                         __u64 args[6];
>                 } entry_info;
>                 struct {
>                         __s64 rval;
>                         __u8 is_error;
>                         __u8 __pad1[7];
>                 } exit_info;
>         };
> };

Should seccomp events use entry_info or should they just literally
supply seccomp_data?