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SubjectRe: [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

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