[tip:x86/mm] x86/boot/compressed/64: Make sure we have a 32-bit code segment

["tip-bot for Kirill A. Shutemov" <tipbot@zytor.com>]

Commit-ID:  7beebaccd5083d61e975acb581bd528b9326e7c4
Gitweb:     https://git.kernel.org/tip/7beebaccd5083d61e975acb581bd528b9326e7c4
Author:     Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
AuthorDate: Mon, 12 Mar 2018 13:02:43 +0300
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 12 Mar 2018 11:49:24 +0100

x86/boot/compressed/64: Make sure we have a 32-bit code segment

When kernel starts in 64-bit mode we inherit the GDT from the bootloader.
It may cause a problem if the GDT doesn't have a 32-bit code segment
where we expect it to be.

Load our own GDT with known segments.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20180312100246.89175-2-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/boot/compressed/head_64.S | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index c813cb004056..f0c3a2f7e528 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -313,6 +313,11 @@ ENTRY(startup_64)
 	 * first.
 	 */
 
+	/* Make sure we have GDT with 32-bit code segment */
+	leaq	gdt(%rip), %rax
+	movq	%rax, gdt64+2(%rip)
+	lgdt	gdt64(%rip)
+
 	/*
 	 * paging_prepare() sets up the trampoline and checks if we need to
 	 * enable 5-level paging.
@@ -547,6 +552,11 @@ no_longmode:
 #include "../../kernel/verify_cpu.S"
 
 	.data
+gdt64:
+	.word	gdt_end - gdt
+	.long	0
+	.word	0
+	.quad   0
 gdt:
 	.word	gdt_end - gdt
 	.long	gdt