09.03.2017 04:11, Ricardo Neri пишет:
On Wed, 2017-03-08 at 19:53 +0300, Stas Sergeev wrote:
08.03.2017 19:46, Andy Lutomirski пишет:
No no, since I meant prot mode, this is not what I need.
I would never need to disable UMIP as to allow the
prot mode apps to do SLDT. Instead it would be good
to have an ability to provide a replacement for the dummy
emulation that is currently being proposed for kernel.
All is needed for this, is just to deliver a SIGSEGV.
That's what I meant.  Turning off FIXUP_UMIP would leave UMIP on but
turn off the fixup, so you'd get a SIGSEGV indicating #GP (or a vm86
GP exit).
But then I am confused with the word "compat" in
your "COMPAT_MASK0_X86_UMIP_FIXUP" and
"sys_adjust_compat_mask(int op, int word, u32 mask);"

Leaving UMIP on and only disabling a fixup doesn't
sound like a compat option to me. I would expect
compat to disable it completely.
I guess that the _UMIP_FIXUP part makes it clear that emulation, not
UMIP is disabled, allowing the SIGSEGV be delivered to the user space
program.

Would having a COMPAT_MASK0_X86_UMIP_FIXUP to disable emulation and a
COMPAT_MASK0_X86_UMIP to disable UMIP make sense?

Also, wouldn't having a COMPAT_MASK0_X86_UMIP to disable UMIP defeat its
purpose? Applications could simply use this compat mask to bypass UMIP
and gain access to the instructions it protects.
I don't think someone will want to completely disable
UMIP, so why do you need such functionality?
My question was only what does "compat" mean
in "COMPAT_MASK0_X86_UMIP_FIXUP", compat with what.
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