[PATCHv7 05/14] x86/boot/efi: Define __KERNEL32_CS GDT on 64-bit configurations

Kirill A. Shutemov
2017-06-06T11:32:30Z

We would need to switch temporarily to compatibility mode during booting
with 5-level paging enabled. It would require 32-bit code segment
descriptor.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
---
arch/x86/boot/compressed/eboot.c | 25 +++++++++++++++++++++++--
1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index b75c20f779ea..c3e869eaef0c 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -1046,8 +1046,29 @@ struct boot_params *efi_main(struct efi_config *c,
memset((char *)gdt->address, 0x0, gdt->size);
desc = (struct desc_struct *)gdt->address;

- /* The first GDT is a dummy and the second is unused. */
- desc += 2;
+ /* The first GDT is a dummy. */
+ desc++;
+
+ if (IS_ENABLED(CONFIG_X86_64)) {
+ /* __KERNEL32_CS */
+ desc->limit0 = 0xffff;
+ desc->base0 = 0x0000;
+ desc->base1 = 0x0000;
+ desc->type = SEG_TYPE_CODE | SEG_TYPE_EXEC_READ;
+ desc->s = DESC_TYPE_CODE_DATA;
+ desc->dpl = 0;
+ desc->p = 1;
+ desc->limit = 0xf;
+ desc->avl = 0;
+ desc->l = 0;
+ desc->d = SEG_OP_SIZE_32BIT;
+ desc->g = SEG_GRANULARITY_4KB;
+ desc->base2 = 0x00;
+ desc++;
+ } else {
+ /* Second entry is unused on 32-bit */
+ desc++;
+ }

/* __KERNEL_CS */
desc->limit0 = 0xffff;
--
2.11.0