linux-kernel - Re: [GIT PULL] x86/topology changes for v5.3

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Date:   Tue, 9 Jul 2019 17:31:07 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Borislav Petkov <bp@...en8.de>, Len Brown <lenb@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Tony Luck <tony.luck@...el.com>, Jiri Kosina <jkosina@...e.cz>,
        Bob Moore <robert.moore@...el.com>,
        Erik Schmauss <erik.schmauss@...el.com>
Subject: Re: [GIT PULL] x86/topology changes for v5.3

On Wed, Jul 10, 2019 at 01:17:11AM +0200, Thomas Gleixner wrote:
> On Wed, 10 Jul 2019, Thomas Gleixner wrote:
> > 
> > That still does not explain the cr4/0 issue you have. Can you send me your
> > .config please?
> 
> Does your machine have UMIP support? None of my test boxes has. So that'd
> be the difference of bits enforced in CR4. Should not matter because it's
> User mode instruction prevention, but who knows.

Ew. Yeah, I don't have i9 nor i7 for testing this. I did try everything
else I had (and hibernation). Is only Linus able to reproduce this so far?

To rule out (in?) UMIP, this would remove UMIP from the pinning:

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 309b6b9b49d4..f3beedb6da8a 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -380,7 +380,7 @@ static void __init setup_cr_pinning(void)
 {
 	unsigned long mask;
 
-	mask = (X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_UMIP);
+	mask = (X86_CR4_SMEP | X86_CR4_SMAP);
 	cr4_pinned_bits = this_cpu_read(cpu_tlbstate.cr4) & mask;
 	static_key_enable(&cr_pinning.key);
 }


-- 
Kees Cook