Messages in this thread | | | Date | Wed, 8 Jul 2015 11:48:56 -0700 | Subject | Re: [PATCH] x86/kconfig/32: Mark CONFIG_VM86 as BROKEN | From | Kees Cook <> |
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On Wed, Jul 8, 2015 at 10:55 AM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > On Wed, Jul 8, 2015 at 10:49 AM, Andy Lutomirski <luto@amacapital.net> wrote: >> >> I don't know how to tell whether something is trying to use real mode, >> but I can play this just fine in DOSEMU on my 64-bit laptop: > > So a 64-bit distro obviously will never have used vm86 mode - it > doesn't work there. Never has. There's no sane way to get to vm86 mode > from long mode, that's just how the 64-bit extensions worked. > > (64-bit hardware obviously does support vm86 mode, but you have to > play games with mixing long mode and CPL0 32-bit protected mode to get > there, and we never did that). > > It's the 32-bit distros I would worry about. The ones that may have > well disabled emulation, because they have vm86 mode enabled.
Speaking as the dosemu maintainer in Debian and Ubuntu, I can confirm what Andy mentioned: dosemu will kick over to emulation if SYS_vm86 and SYS_vm86old fail. The other area I remember that used vm86 mode was non-KMS Xorg drivers and anything using svgalib that tried to do video card BIOS initialization.
Also, Andy, I think you weren't looking at i386 builds of Ubuntu. Current Ubuntu, and 12.04 ("Precise") LTS (supported until 2017), and 14.04 LTS (until 2019) releases all have CONFIG_VM86.
-Kees
-- Kees Cook Chrome OS Security
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