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    SubjectRE: [PATCH] x86 : Ensure X86_FLAGS_NT is cleared on syscall entry
    Date
    > -----Original Message-----
    > From: Chuck Ebbert [mailto:cebbert.lkml@gmail.com]
    > Sent: Friday, September 26, 2014 3:01 PM
    > To: Anish Bhatt
    > Cc: linux-kernel@vger.kernel.org; x86@kernel.org; tglx@linutronix.de;
    > mingo@redhat.com; hpa@zytor.com; sebastian@fds-team.de; Linus
    > Torvalds
    > Subject: Re: [PATCH] x86 : Ensure X86_FLAGS_NT is cleared on syscall entry
    >
    > On Thu, 25 Sep 2014 12:42:51 -0700
    > Anish Bhatt <anish@chelsio.com> wrote:
    >
    > > The MSR_SYSCALL_MASK, which is responsible for clearing specific
    > > EFLAGS on syscall entry, should also clear the nested task (NT) flag
    > > to be safe from userspace injection. Without this fix the application
    > > segmentation faults on syscall return because of the changed meaning
    > > of the IRET instruction.
    > >
    > > Further details can be seen here
    > > https://bugs.winehq.org/show_bug.cgi?id=33275
    > >
    > > Signed-off-by: Anish Bhatt <anish@chelsio.com>
    > > Signed-off-by: Sebastian Lackner <sebastian@fds-team.de>
    > > ---
    > > arch/x86/kernel/cpu/common.c | 2 +-
    > > 1 file changed, 1 insertion(+), 1 deletion(-)
    > >
    > > diff --git a/arch/x86/kernel/cpu/common.c
    > > b/arch/x86/kernel/cpu/common.c index e4ab2b4..3126558 100644
    > > --- a/arch/x86/kernel/cpu/common.c
    > > +++ b/arch/x86/kernel/cpu/common.c
    > > @@ -1184,7 +1184,7 @@ void syscall_init(void)
    > > /* Flags to clear on syscall */
    > > wrmsrl(MSR_SYSCALL_MASK,
    > > X86_EFLAGS_TF|X86_EFLAGS_DF|X86_EFLAGS_IF|
    > > - X86_EFLAGS_IOPL|X86_EFLAGS_AC);
    > > + X86_EFLAGS_IOPL|X86_EFLAGS_AC|X86_EFLAGS_NT);
    > > }
    > >
    > > /*
    >
    > I don't get it. Why isn't this patch acceptable, at least on x86-64 where NT is
    > never valid?
    >
    > Bueller?

    Chuck, I don't think anyone has gotten around to reviewing, accepting or
    rejecting this patch yet.
    -Anish


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