git: bdf0f24bb16d - main - linux: implement PTRACE_GET_SYSCALL_INFO

[Konstantin Belousov]

On Wed, Sep 15, 2021 at 02:15:59AM +0300, Konstantin Belousov wrote:
> On Tue, Sep 14, 2021 at 11:54:08PM +0100, Jessica Clarke wrote:
> > On 14 Sep 2021, at 23:45, Konstantin Belousov <kostikbel at gmail.com> wrote:
> > > 
> > > On Tue, Sep 14, 2021 at 08:41:06PM +0000, Edward Tomasz Napierala wrote:
> > >> The branch main has been updated by trasz:
> > >> 
> > >> URL: https://cgit.FreeBSD.org/src/commit/?id=bdf0f24bb16d556a5b1e01cdfc087d08e91ac572
> > >> 
> > >> commit bdf0f24bb16d556a5b1e01cdfc087d08e91ac572
> > >> Author:     Edward Tomasz Napierala <trasz at FreeBSD.org>
> > >> AuthorDate: 2021-09-12 11:31:10 +0000
> > >> Commit:     Edward Tomasz Napierala <trasz at FreeBSD.org>
> > >> CommitDate: 2021-09-14 20:19:55 +0000
> > >> 
> > >>    linux: implement PTRACE_GET_SYSCALL_INFO
> > >> 
> > >>    This is one of the pieces required to make modern (ie Focal)
> > >>    strace(1) work.
> > >> 
> > >>    Reviewed By:    jhb (earlier version)
> > >>    Sponsored by:   EPSRC
> > >>    Differential Revision:  https://reviews.freebsd.org/D28212
> > >> ---
> > >> lib/libsysdecode/mktables             |  2 +-
> > >> sys/amd64/linux/linux_ptrace.c        | 98 +++++++++++++++++++++++++++++++++--
> > >> sys/compat/freebsd32/freebsd32_misc.c |  3 ++
> > >> sys/kern/sys_process.c                | 17 ++++++
> > >> sys/sys/ptrace.h                      |  4 ++
> > >> 5 files changed, 120 insertions(+), 4 deletions(-)
> > >> 
> > >> +	case PT_GET_SC_ARGS_ALL:
> > >> +		CTR1(KTR_PTRACE, "PT_GET_SC_ARGS_ALL: pid %d", p->p_pid);
> > >> +		if ((td2->td_dbgflags & (TDB_SCE | TDB_SCX)) == 0
> > >> +#ifdef COMPAT_FREEBSD32
> > >> +		    || (wrap32 && !safe)
> > >> +#endif
> > >> +		    ) {
> > >> +			error = EINVAL;
> > >> +			break;
> > >> +		}
> > >> +		bcopy(td2->td_sa.args, addr, sizeof(td2->td_sa.args));
> > >> +		break;
> > > 
> > > This is awful, you already got that feedback in review, as I read it.
> > > I strongly suggest to remove PT_GET_SC_ARGS_ALL, and instead checks something
> > > in the implementation of PT_GET_SC_ARGS to select either full copy or just
> > > nargs args.
> > > 
> > > Easiest thing for 'something' would be SV_PROC_ABI(p) == SV_ABI_LINUX.
> > 
> > That is incorrect. The original review just changed PT_GET_SC_ARGS even
> > for FreeBSD and that was what was described as horrible. John suggested
> > two alternatives: this approach, and having the Linuxulator bypass
> > kern_ptrace entirely by doing its own thing.
> My view is that
> - the whole thing with reading past nargs is horrible
> - having hidden API interface is horrible, it is obvious layering violation
>   when you need to hide an API: the consumer calls at the wrong level.
> 
> Another reason to dislike this is that we started to add new PT_ verbs
> at relatively high rate recently.  I am aware of at least to more PT_
> ops coming in.  In other words, we are not too far from exhausting the
> MI range and then we would need to make some arrangements.  Having one
> more PT_ value, esp. not useful for anything but for layering violation,
> is not good.

https://reviews.freebsd.org/D31968