linux-kernel - [PATCH 4.19 72/90] x86/boot/compressed/64: Do not corrupt EDX on EFER.LME=1 setting

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Date:   Mon,  8 Jul 2019 17:13:39 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Kyle D Pelton <kyle.d.pelton@...el.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Borislav Petkov <bp@...e.de>, dave.hansen@...ux.intel.com,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Wei Huang <wei@...hat.com>, x86-ml <x86@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 72/90] x86/boot/compressed/64: Do not corrupt EDX on EFER.LME=1 setting

[ Upstream commit 45b13b424faafb81c8c44541f093a682fdabdefc ]

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
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 */
-- 
2.20.1