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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Sun, 21 Aug 2011 18:09:00 -0700
Message-ID: <CA+55aFztZ=r5wa0x26KJQxvZOaQq8s2v3u50wCyJcA-Sc4g8gQ@mail.gmail.com>
Subject: Re: SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird
 crap with vdso on uml/i386)
To: Andrew Lutomirski <luto@mit.edu>
Cc: Al Viro <viro@zeniv.linux.org.uk>, "H. Peter Anvin" <hpa@zytor.com>,
        mingo@redhat.com, Richard Weinberger <richard@nod.at>,
        user-mode-linux-devel@lists.sourceforge.net,
        linux-kernel@vger.kernel.org
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On Sun, Aug 21, 2011 at 5:44 PM, Andrew Lutomirski <luto@mit.edu> wrote:
>
> Which suggests an easy-ish fix: if sysenter is used or if syscall is
> entered from the EIP is is supposed to be entered from, then just
> change ip in the argument save to point to the int 0x80 instruction.

Indeed. Just add an "int 0x80" instruction to the vsyscall thing, and
you'd be done.

In fact, just replace the

  jmp .Lenter_kernel

with

  int 0x80

and you'd be pretty much all done, no?

(Ok, that's probably a huge over-simplification, but perhaps "close
enough" to true that it would be workable)

                     Linus