From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Subject: Re: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention
Date: Wed, 08 Mar 2017 17:11:49 -0800
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To: Stas Sergeev <stsp@list.ru>
Cc: Andy Lutomirski <luto@amacapital.net>, Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>, Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@suse.de>, Peter Zijlstra <peterz@infradead.org>, Andrew Morton <akpm@linux-foundation.org>, Brian Gerst <brgerst@gmail.com>, Chris Metcalf <cmetcalf@mellanox.com>, Dave Hansen <dave.hansen@linux.intel.com>, Paolo Bonzini <pbonzini@redhat.com>, Liang Z Li <liang.z.li@intel.com>, Masami Hiramatsu <mhiramat@kernel.org>, Huang Rui <ray.huang@amd.com>, Jiri Slaby <jslaby@suse.cz>, Jonathan Corbet <corbet@lwn.net>, "Michael S. Tsirkin" <mst@redhat.com>, Paul Gortmaker <paul.gortmaker@windriver.com>, Vlastimil Babka <vbabka@suse.cz>, Chen Yucong <>

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.

Thanks and BR,
Ricardo