linux-kernel - Re: [patch V3 00/20] x86/iopl: Prevent user space from using CLI/STI with iopl(3)

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Date:   Thu, 14 Nov 2019 09:43:45 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Willy Tarreau <w@....eu>, Juergen Gross <jgross@...e.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [patch V3 00/20] x86/iopl: Prevent user space from using CLI/STI
 with iopl(3)

On Wed, Nov 13, 2019 at 09:42:40PM +0100, Thomas Gleixner wrote:

> iopl(level = 3) enables aside of access to all 65536 I/O ports also the
> usage of CLI/STI in user space.
> 
> Disabling interrupts in user space can lead to system lockups and breaks
> assumptions in the kernel that userspace always runs with interrupts
> enabled.
> 
> iopl() is often preferred over ioperm() as it avoids the overhead of
> copying the tasks I/O bitmap to the TSS bitmap on context switch. This
> overhead can be avoided by providing a all zeroes bitmap in the TSS and
> switching the TSS bitmap offset to this permit all IO bitmap. It's
> marginally slower than iopl() which is a one time setup, but prevents the
> usage of CLI/STI in user space.

> ---
>  arch/x86/Kconfig                        |   18 ++
>  arch/x86/entry/common.c                 |    4 
>  arch/x86/include/asm/io_bitmap.h        |   29 ++++
>  arch/x86/include/asm/paravirt.h         |    4 
>  arch/x86/include/asm/paravirt_types.h   |    2 
>  arch/x86/include/asm/pgtable_32_types.h |    2 
>  arch/x86/include/asm/processor.h        |  113 ++++++++++-------
>  arch/x86/include/asm/ptrace.h           |    6 
>  arch/x86/include/asm/switch_to.h        |   10 +
>  arch/x86/include/asm/thread_info.h      |   14 +-
>  arch/x86/include/asm/xen/hypervisor.h   |    2 
>  arch/x86/kernel/cpu/common.c            |  188 ++++++++++++----------------
>  arch/x86/kernel/doublefault.c           |    2 
>  arch/x86/kernel/ioport.c                |  209 +++++++++++++++++++++-----------
>  arch/x86/kernel/paravirt.c              |    2 
>  arch/x86/kernel/process.c               |  200 ++++++++++++++++++++++++------
>  arch/x86/kernel/process_32.c            |   77 -----------
>  arch/x86/kernel/process_64.c            |   86 -------------
>  arch/x86/kernel/ptrace.c                |   12 +
>  arch/x86/kvm/vmx/vmx.c                  |    8 -
>  arch/x86/mm/cpu_entry_area.c            |    8 +
>  arch/x86/xen/enlighten_pv.c             |   10 -
>  tools/testing/selftests/x86/ioperm.c    |   16 ++
>  tools/testing/selftests/x86/iopl.c      |  129 ++++++++++++++++++-
>  24 files changed, 674 insertions(+), 477 deletions(-)


Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>