linux-kernel - [tip: x86/urgent] x86/pkeys: Manually set X86_FEATURE

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Message-ID: <158282687050.28353.6531125831614540420.tip-bot2@tip-bot2>
Date:   Thu, 27 Feb 2020 18:07:50 -0000
From:   "tip-bot2 for Sean Christopherson" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Jacob Keller <jacob.e.keller@...el.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        stable@...r.kernel.org, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: x86/urgent] x86/pkeys: Manually set X86_FEATURE_OSPKE to
 preserve existing changes

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     735a6dd02222d8d070c7bb748f25895239ca8c92
Gitweb:        https://git.kernel.org/tip/735a6dd02222d8d070c7bb748f25895239ca8c92
Author:        Sean Christopherson <sean.j.christopherson@...el.com>
AuthorDate:    Wed, 26 Feb 2020 15:16:15 -08:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Thu, 27 Feb 2020 19:02:45 +01:00

x86/pkeys: Manually set X86_FEATURE_OSPKE to preserve existing changes

Explicitly set X86_FEATURE_OSPKE via set_cpu_cap() instead of calling
get_cpu_cap() to pull the feature bit from CPUID after enabling CR4.PKE.
Invoking get_cpu_cap() effectively wipes out any {set,clear}_cpu_cap()
changes that were made between this_cpu->c_init() and setup_pku(), as
all non-synthetic feature words are reinitialized from the CPU's CPUID
values.

Blasting away capability updates manifests most visibility when running
on a VMX capable CPU, but with VMX disabled by BIOS.  To indicate that
VMX is disabled, init_ia32_feat_ctl() clears X86_FEATURE_VMX, using
clear_cpu_cap() instead of setup_clear_cpu_cap() so that KVM can report
which CPU is misconfigured (KVM needs to probe every CPU anyways).
Restoring X86_FEATURE_VMX from CPUID causes KVM to think VMX is enabled,
ultimately leading to an unexpected #GP when KVM attempts to do VMXON.

Arguably, init_ia32_feat_ctl() should use setup_clear_cpu_cap() and let
KVM figure out a different way to report the misconfigured CPU, but VMX
is not the only feature bit that is affected, i.e. there is precedent
that tweaking feature bits via {set,clear}_cpu_cap() after ->c_init()
is expected to work.  Most notably, x86_init_rdrand()'s clearing of
X86_FEATURE_RDRAND when RDRAND malfunctions is also overwritten.

Fixes: 0697694564c8 ("x86/mm/pkeys: Actually enable Memory Protection Keys in the CPU")
Reported-by: Jacob Keller <jacob.e.keller@...el.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>
Tested-by: Jacob Keller <jacob.e.keller@...el.com>
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/20200226231615.13664-1-sean.j.christopherson@intel.com
---
 arch/x86/kernel/cpu/common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 52c9bfb..4cdb123 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -445,7 +445,7 @@ static __always_inline void setup_pku(struct cpuinfo_x86 *c)
 	 * cpuid bit to be set.  We need to ensure that we
 	 * update that bit in this CPU's "cpu_info".
 	 */
-	get_cpu_cap(c);
+	set_cpu_cap(c, X86_FEATURE_OSPKE);
 }

 #ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS