linux-kernel - [PATCH 2/7] x86/boot/compressed/64: Reload CS in startup

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Message-Id: <20210210102135.30667-3-joro@8bytes.org>
Date:   Wed, 10 Feb 2021 11:21:30 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     x86@...nel.org
Cc:     Joerg Roedel <joro@...tes.org>, Joerg Roedel <jroedel@...e.de>,
        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>,
        Kees Cook <keescook@...omium.org>,
        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>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: [PATCH 2/7] x86/boot/compressed/64: Reload CS in startup_32

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

Exception handling in the startup_32 boot path requires the CS
selector to be correctly set up. Reload it from the current GDT.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/boot/compressed/head_64.S | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index e94874f4bbc1..c59c80ca546d 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -107,9 +107,16 @@ SYM_FUNC_START(startup_32)
 	movl	%eax, %gs
 	movl	%eax, %ss
 
-/* setup a stack and make sure cpu supports long mode. */
+	/* Setup a stack and load CS from current GDT */
 	leal	rva(boot_stack_end)(%ebp), %esp
 
+	pushl	$__KERNEL32_CS
+	leal	rva(1f)(%ebp), %eax
+	pushl	%eax
+	lretl
+1:
+
+	/* Make sure cpu supports long mode. */
 	call	verify_cpu
 	testl	%eax, %eax
 	jnz	.Lno_longmode
-- 
2.30.0