linux-kernel - [tip:x86/urgent] x86/boot/compressed/64: Do not corrupt EDX on EFER.LME=1 setting

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Date:   Wed, 6 Feb 2019 10:04:11 -0800
From:   "tip-bot for Kirill A. Shutemov" <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     kyle.d.pelton@...el.com, mingo@...hat.com, x86@...nel.org,
        hpa@...or.com, linux-kernel@...r.kernel.org, bp@...e.de,
        wei@...hat.com, mingo@...nel.org, tglx@...utronix.de,
        kirill.shutemov@...ux.intel.com
Subject: [tip:x86/urgent] x86/boot/compressed/64: Do not corrupt EDX on
 EFER.LME=1 setting

Commit-ID:  45b13b424faafb81c8c44541f093a682fdabdefc
Gitweb:     https://git.kernel.org/tip/45b13b424faafb81c8c44541f093a682fdabdefc
Author:     Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
AuthorDate: Wed, 6 Feb 2019 14:52:53 +0300
Committer:  Borislav Petkov <bp@...e.de>
CommitDate: Wed, 6 Feb 2019 18:56:18 +0100

x86/boot/compressed/64: Do not corrupt EDX on EFER.LME=1 setting

RDMSR in the trampoline code overwrites EDX but that register is used
to indicate whether 5-level paging has to be enabled and if clobbered,
leads to failure to boot on a 5-level paging machine.

Preserve EDX on the stack while we are dealing with EFER.

Fixes: b677dfae5aa1 ("x86/boot/compressed/64: Set EFER.LME=1 in 32-bit trampoline before returning to long mode")
Reported-by: Kyle D Pelton <kyle.d.pelton@...el.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: dave.hansen@...ux.intel.com
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Wei Huang <wei@...hat.com>
Cc: x86-ml <x86@...nel.org>
Link: https://lkml.kernel.org/r/20190206115253.1907-1-kirill.shutemov@linux.intel.com
---
 arch/x86/boot/compressed/head_64.S | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index f105ae8651c9..f62e347862cc 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -602,10 +602,12 @@ ENTRY(trampoline_32bit_src)
 3:
 	/* Set EFER.LME=1 as a precaution in case hypervsior pulls the rug */
 	pushl	%ecx
+	pushl	%edx
 	movl	$MSR_EFER, %ecx
 	rdmsr
 	btsl	$_EFER_LME, %eax
 	wrmsr
+	popl	%edx
 	popl	%ecx
 
 	/* Enable PAE and LA57 (if required) paging modes */