linux-kernel - Re: [PATCH] entry: Fix missed trap after single-step on system call return

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Message-ID: <CAHk-=wj3j8Fb-5FM8y+Oz+QWQ61ZxS5JW7da+dQeXrOYnOc19Q@mail.gmail.com>
Date:   Wed, 3 Feb 2021 10:22:08 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Gabriel Krisman Bertazi <krisman@...labora.com>,
        Kyle Huey <me@...ehuey.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        open list <linux-kernel@...r.kernel.org>,
        "Robert O'Callahan" <rocallahan@...il.com>
Subject: Re: [PATCH] entry: Fix missed trap after single-step on system call return

On Wed, Feb 3, 2021 at 10:18 AM Andy Lutomirski <luto@...nel.org> wrote:
>
> So if we want to reliably single-step a system call and trap after the
> system call, we just need to synthesize a trap on the way out.

Well, I think Gabriel's patch does exactly that, due to how
SYSCALL_EXIT_TRAP is set. It looks like subsequent system calls will
work exactly the way the concurrent system call case (that Kyle's test
did) does.

So it all _looks_ sane to me, but this is one of those "it needs testing".

               Linus