linux-kernel - Re: [REGRESSION] x86/entry: TIF_SINGLESTEP handling is still broken

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Message-ID: <CAOp6jLaKR3zJDg9bNFkTcj78kKDtrdnMF4U-mxzkXDRgHu94GA@mail.gmail.com>
Date:   Mon, 1 Feb 2021 15:25:44 +1300
From:   "Robert O'Callahan" <rocallahan@...il.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Kyle Huey <me@...ehuey.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [REGRESSION] x86/entry: TIF_SINGLESTEP handling is still broken

On Mon, Feb 1, 2021 at 12:40 PM Andy Lutomirski <luto@...nel.org> wrote:
> I admit that PTRACE_SINGLESTEP seems like an odd way to spell "advance
> to the end of the syscall", but you're right, it should work.

We don't know of any better way to advance to the end of the syscall
without executing any userspace instructions. We could set a
breakpoint at the syscall return address but weird edge cases
complicate that.

Rob
-- 
"He was pierced for our transgressions, he was crushed for our
iniquities; the punishment that brought us peace was upon him, and by
his wounds we are healed. We all, like sheep, have gone astray, each
of us has turned to his own way; and the LORD has laid on him the
iniquity of us all." [Isaiah 53:5-6]