[PATCH v6 32/76] x86/head/64: Load GDT after switch to virtual addresses

Joerg Roedel
2020-08-24T09:13:50Z

From: Joerg Roedel <jroedel@suse.de>

Load the GDT right after switching to virtual addresses to make sure
there is a defined GDT for exception handling.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20200724160336.5435-32-joro@8bytes.org
---
arch/x86/kernel/head_64.S | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 800053219054..f958d4e4ee08 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -166,6 +166,14 @@ SYM_CODE_START(secondary_startup_64)
1:
UNWIND_HINT_EMPTY

+ /*
+ * We must switch to a new descriptor in kernel space for the GDT
+ * because soon the kernel won't have access anymore to the userspace
+ * addresses where we're currently running on. We have to do that here
+ * because in 32bit we couldn't load a 64bit linear address.
+ */
+ lgdt early_gdt_descr(%rip)
+
/* Check if nx is implemented */
movl $0x80000001, %eax
cpuid
@@ -193,14 +201,6 @@ SYM_CODE_START(secondary_startup_64)
pushq $0
popfq

- /*
- * We must switch to a new descriptor in kernel space for the GDT
- * because soon the kernel won't have access anymore to the userspace
- * addresses where we're currently running on. We have to do that here
- * because in 32bit we couldn't load a 64bit linear address.
- */
- lgdt early_gdt_descr(%rip)
-
/* set up data segments */
xorl %eax,%eax
movl %eax,%ds
--
2.28.0