linux-kernel - [tip: x86/seves] x86/head/64: Switch to initial stack earlier

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Message-ID: <159972973918.20229.8742099836749431075.tip-bot2@tip-bot2>
Date:   Thu, 10 Sep 2020 09:22:19 -0000
From:   "tip-bot2 for Joerg Roedel" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Joerg Roedel <jroedel@...e.de>, Borislav Petkov <bp@...e.de>,
        Kees Cook <keescook@...omium.org>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: x86/seves] x86/head/64: Switch to initial stack earlier

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

Commit-ID:     3add38cb96a1ae7d152db69ab4329e809c2af2d4
Gitweb:        https://git.kernel.org/tip/3add38cb96a1ae7d152db69ab4329e809c2af2d4
Author:        Joerg Roedel <jroedel@...e.de>
AuthorDate:    Mon, 07 Sep 2020 15:15:33 +02:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Mon, 07 Sep 2020 21:44:01 +02:00

x86/head/64: Switch to initial stack earlier

Make sure there is a stack once the kernel runs from virtual addresses.
At this stage any secondary CPU which boots will have lost its stack
because the kernel switched to a new page-table which does not map the
real-mode stack anymore.

This is needed for handling early #VC exceptions caused by instructions
like CPUID.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Kees Cook <keescook@...omium.org>
Link: https://lkml.kernel.org/r/20200907131613.12703-33-joro@8bytes.org
---
 arch/x86/kernel/head_64.S |  9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index f402087..83050c9 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -192,6 +192,12 @@ SYM_CODE_START(secondary_startup_64)
 	movl	initial_gs+4(%rip),%edx
 	wrmsr
 
+	/*
+	 * Setup a boot time stack - Any secondary CPU will have lost its stack
+	 * by now because the cr3-switch above unmaps the real-mode stack
+	 */
+	movq initial_stack(%rip), %rsp
+
 	/* Check if nx is implemented */
 	movl	$0x80000001, %eax
 	cpuid
@@ -212,9 +218,6 @@ SYM_CODE_START(secondary_startup_64)
 	/* Make changes effective */
 	movq	%rax, %cr0
 
-	/* Setup a boot time stack */
-	movq initial_stack(%rip), %rsp
-
 	/* zero EFLAGS after setting rsp */
 	pushq $0
 	popfq