linux-kernel - [PATCH v7 30/72] x86/head/64: Load GDT after switch to virtual addresses

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Date:   Mon,  7 Sep 2020 15:15:31 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     x86@...nel.org
Cc:     Joerg Roedel <joro@...tes.org>, Joerg Roedel <jroedel@...e.de>,
        Kees Cook <keescook@...omium.org>, hpa@...or.com,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Martin Radev <martin.b.radev@...il.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: [PATCH v7 30/72] x86/head/64: Load GDT after switch to virtual addresses

From: Joerg Roedel <jroedel@...e.de>

Load the GDT right after switching to virtual addresses to make sure
there is a defined GDT for exception handling.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
Reviewed-by: Kees Cook <keescook@...omium.org>
---
 arch/x86/kernel/head_64.S | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 2b2e91627221..03b03f266dc1 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -158,6 +158,14 @@ SYM_CODE_START(secondary_startup_64)
 1:
 	UNWIND_HINT_EMPTY
 
+	/*
+	 * We must switch to a new descriptor in kernel space for the GDT
+	 * because soon the kernel won't have access anymore to the userspace
+	 * addresses where we're currently running on. We have to do that here
+	 * because in 32bit we couldn't load a 64bit linear address.
+	 */
+	lgdt	early_gdt_descr(%rip)
+
 	/* Check if nx is implemented */
 	movl	$0x80000001, %eax
 	cpuid
@@ -185,14 +193,6 @@ SYM_CODE_START(secondary_startup_64)
 	pushq $0
 	popfq
 
-	/*
-	 * We must switch to a new descriptor in kernel space for the GDT
-	 * because soon the kernel won't have access anymore to the userspace
-	 * addresses where we're currently running on. We have to do that here
-	 * because in 32bit we couldn't load a 64bit linear address.
-	 */
-	lgdt	early_gdt_descr(%rip)
-
 	/* set up data segments */
 	xorl %eax,%eax
 	movl %eax,%ds
-- 
2.28.0