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    SubjectRe: [patch V3 17/20] x86/iopl: Restrict iopl() permission scope
    On Wed, Nov 13, 2019 at 09:42:57PM +0100, Thomas Gleixner wrote:
    > From: Thomas Gleixner <tglx@linutronix.de>
    >
    > The access to the full I/O port range can be also provided by the TSS I/O
    > bitmap, but that would require to copy 8k of data on scheduling in the
    > task. As shown with the sched out optimization TSS.io_bitmap_base can be
    > used to switch the incoming task to a preallocated I/O bitmap which has all
    > bits zero, i.e. allows access to all I/O ports.
    >
    > Implementing this allows to provide an iopl() emulation mode which restricts
    > the IOPL level 3 permissions to I/O port access but removes the STI/CLI
    > permission which is coming with the hardware IOPL mechansim.
    >
    > Provide a config option to switch IOPL to emulation mode, make it the
    > default and while at it also provide an option to disable IOPL completely.
    >
    > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    > Acked-by: Andy Lutomirski <luto@kernel.org>
    > ---
    > V3: Folded the missing NULL pointer check, reduced preempt disable
    > scope (Ingo)
    >
    > V2: Fixed the 32bit build fail by increasing the cpu entry area size
    > Move the TSS update out of the iopl() emulation code.
    > ---
    > arch/x86/Kconfig | 32 +++++++++++
    > arch/x86/include/asm/pgtable_32_types.h | 2
    > arch/x86/include/asm/processor.h | 28 +++++++---
    > arch/x86/kernel/cpu/common.c | 5 +
    > arch/x86/kernel/ioport.c | 87 ++++++++++++++++++++++----------
    > arch/x86/kernel/process.c | 28 ++++++----
    > 6 files changed, 137 insertions(+), 45 deletions(-)
    >
    > --- a/arch/x86/Kconfig
    > +++ b/arch/x86/Kconfig
    > @@ -1254,6 +1254,38 @@ config X86_VSYSCALL_EMULATION
    > Disabling this option saves about 7K of kernel size and
    > possibly 4K of additional runtime pagetable memory.
    >
    > +choice
    > + prompt "IOPL"
    > + default X86_IOPL_EMULATION
    > +
    > +config X86_IOPL_EMULATION
    > + bool "IOPL Emulation"
    > + ---help---
    > + Legacy IOPL support is an overbroad mechanism which allows user
    > + space aside of accessing all 65536 I/O ports also to disable
    > + interrupts. To gain this access the caller needs CAP_SYS_RAWIO
    > + capabilities and permission from eventually active security

    I think you mean here: s/eventually/potentially/ or so. "eventually" is
    one of the false friends. :)

    --
    Regards/Gruss,
    Boris.

    https://people.kernel.org/tglx/notes-about-netiquette

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