Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     linux-kernel@vger.kernel.org
Cc:     x86@kernel.org, Andy Lutomirski <luto@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@redhat.com>,
        kvm@vger.kernel.org, "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Rik van Riel <riel@surriel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: [PATCH 25/29] x86/fpu: Update xstate's PKRU value on write_pkru()
Date:   Wed, 28 Nov 2018 23:20:31 +0100
Message-Id: <20181128222035.2996-26-bigeasy@linutronix.de>
In-Reply-To: <20181128222035.2996-1-bigeasy@linutronix.de>
References: <20181128222035.2996-1-bigeasy@linutronix.de>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

During the context switch the xstate is loaded which also includes the
PKRU value.
If xstate is restored on return to userland it is required that the
PKRU value in xstate is the same as the one in the CPU.

Save the PKRU in xstate during modification.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 arch/x86/include/asm/pgtable.h | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 40616e8052924..5eed44798ae95 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -23,6 +23,8 @@
 
 #ifndef __ASSEMBLY__
 #include <asm/x86_init.h>
+#include <asm/fpu/xstate.h>
+#include <asm/fpu/api.h>
 
 extern pgd_t early_top_pgt[PTRS_PER_PGD];
 int __init __early_make_pgtable(unsigned long address, pmdval_t pmd);
@@ -133,8 +135,22 @@ static inline u32 read_pkru(void)
 
 static inline void write_pkru(u32 pkru)
 {
-	if (boot_cpu_has(X86_FEATURE_OSPKE))
-		__write_pkru(pkru);
+	struct pkru_state *pk;
+
+	if (!boot_cpu_has(X86_FEATURE_OSPKE))
+		return;
+
+	pk = get_xsave_addr(&current->thread.fpu.state.xsave, XFEATURE_PKRU);
+	/*
+	 * The PKRU value in xstate needs to be in sync with the value that is
+	 * written to the CPU. The FPU restore on return to userland would
+	 * otherwise load the previous value again.
+	 */
+	__fpregs_changes_begin();
+	if (pk)
+		pk->pkru = pkru;
+	__write_pkru(pkru);
+	__fpregs_changes_end();
 }
 
 static inline int pte_young(pte_t pte)
-- 
2.20.0.rc1