On Thu, Jul 9, 2015 at 11:40 AM, Andy Lutomirski <l...@kernel.org> wrote: > VM86 is entirely broken if ptrace, syscall auditing, or NOHZ_FULL is > in use. The code is a big undocumented mess, it's a real PITA to > test, and it looks like a big chunk of vm86_32.c is dead code. It > also plays awful games with the entry asm. > > No one should be using it anyway. Use DOSBOX or KVM instead. > > Let's accelerate its slow death. Remove it from EXPERT and default > it to n. Distros should not enable it. In the unlikely event that > some user needs it, they can easily re-enable it. > > I've confirmed that 'make oldconfig' will set leave it set to y, so > there should be little or no unexpected breakage from this change. > > Signed-off-by: Andy Lutomirski <l...@kernel.org>
Acked-by: Kees Cook <keesc...@chromium.org> -Kees > --- > arch/x86/Kconfig | 26 ++++++++++++++++++++------ > 1 file changed, 20 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index aa94fd014fa2..b54994a28168 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -997,14 +997,28 @@ config X86_THERMAL_VECTOR > depends on X86_MCE_INTEL > > config VM86 > - bool "Enable VM86 support" if EXPERT > - default y > + bool "Enable VM86 support" > + default n > depends on X86_32 > ---help--- > - This option is required by programs like DOSEMU to run > - 16-bit real mode legacy code on x86 processors. It also may > - be needed by software like XFree86 to initialize some video > - cards via BIOS. Disabling this option saves about 6K. > + This option allows user programs to put the CPU into V8086 > + mode, which is an 80286-era approximation of 16-bit real mode. > + > + Some very old versions of X and/or vbetool require this option > + for user mode setting. Similarly, DOSEMU will use it if > + available to accelerate real mode DOS programs. However, any > + recent version of DOSEMU, X, or vbetool should be fully > + functional even without kernel VM86 support, as they will all > + fall back to software emulation. > + > + Anything that works on a 64-bit kernel is unlikely to need > + this option, as 64-bit kernels don't, and can't, support V8086 > + mode. > + > + Unless you use very old userspace or need the last drop of > + performance in your real mode DOS games and can't use KVM, say > + N here. It disables a fairly large attack surface in the > + kernel. > > config X86_16BIT > bool "Enable support for 16-bit segments" if EXPERT > -- > 2.4.3 > -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
