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>

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index c813cb0..f0c3a2f 100644 (file)
--- 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