linux-kernel - Re: [PATCH] x86/umip: Add a umip= cmdline switch

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Message-ID: <YUDTCgEOZ3JOMSl7@zn.tnic>
Date:   Tue, 14 Sep 2021 18:51:22 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Marcus Rückert <mrueckert@...e.com>
Subject: Re: [PATCH] x86/umip: Add a umip= cmdline switch

On Mon, Sep 13, 2021 at 02:38:36PM -0700, Ricardo Neri wrote:
> That is right. Although, I am not sure programs you can have in
> the same machine that also want to use UMIP-protected instructions.

Sure, another game. :-P

But srsly, looking at those two:

        umip_pr_warn(regs, "%s instruction cannot be used by applications.\n",
                        umip_insns[umip_inst]);

        umip_pr_warn(regs, "For now, expensive software emulation returns the result.\n");

Why are they there at all?

I mean, I can hardly imagine userspace doing anything about them.

They're all likely old, arcane applications or games run in wine which
people have no access to the source code anyway so come to think of it,
the once thing is starting to make more sense to me now.

Sure, that:

        umip_pr_err(regs, "segfault in emulation. error%x\n",
                    X86_PF_USER | X86_PF_WRITE);

should be issued unconditionally but I'm wondering if those warning
messages are needed at all. And if not, I should probably simply rip
them all out.

Or at least silence them by default and flip the cmdline switch logic to
enable them for users who are interested in those things but they should
be silent by default.

I.e., you'd need to supply

	umip=warnings_on

on the cmdline to actually see them.

Hmmm?

-- 
Regards/Gruss,
    Boris.

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