[PATCH v3 31/75] x86/head/64: Install boot GDT

Joerg Roedel
2020-04-28T15:22:57Z

From: Joerg Roedel <jroedel@suse.de>

Handling exceptions during boot requires a working GDT. The kernel GDT
is not yet ready for use, so install a temporary boot GDT.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/kernel/head_64.S | 36 ++++++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 4bbc770af632..11a28c1fb51f 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -72,6 +72,26 @@ SYM_CODE_START_NOALIGN(startup_64)
/* Set up the stack for verify_cpu(), similar to initial_stack below */
leaq (__end_init_task - SIZEOF_PTREGS)(%rip), %rsp

+ /* Setup boot GDT descriptor and load boot GDT */
+ leaq boot_gdt(%rip), %rax
+ movq %rax, boot_gdt_base(%rip)
+ lgdt boot_gdt_descr(%rip)
+
+ /* New GDT is live - reload data segment registers */
+ movl $__KERNEL_DS, %eax
+ movl %eax, %ds
+ movl %eax, %ss
+ movl %eax, %es
+
+ /* Now switch to __KERNEL_CS so IRET works reliably */
+ pushq $__KERNEL_CS
+ leaq .Lon_kernel_cs(%rip), %rax
+ pushq %rax
+ lretq
+
+.Lon_kernel_cs:
+ UNWIND_HINT_EMPTY
+
/* Sanitize CPU configuration */
call verify_cpu

@@ -480,6 +500,22 @@ SYM_DATA_LOCAL(early_gdt_descr_base, .quad INIT_PER_CPU_VAR(gdt_page))
SYM_DATA(phys_base, .quad 0x0)
EXPORT_SYMBOL(phys_base)

+/* Boot GDT used when kernel addresses are not mapped yet */
+SYM_DATA_LOCAL(boot_gdt_descr, .word boot_gdt_end - boot_gdt)
+SYM_DATA_LOCAL(boot_gdt_base, .quad 0)
+SYM_DATA_START(boot_gdt)
+ .quad 0
+ .quad 0x00cf9a000000ffff /* __KERNEL32_CS */
+ .quad 0x00af9a000000ffff /* __KERNEL_CS */
+ .quad 0x00cf92000000ffff /* __KERNEL_DS */
+ .quad 0 /* __USER32_CS - unused */
+ .quad 0 /* __USER_DS - unused */
+ .quad 0 /* __USER_CS - unused */
+ .quad 0 /* unused */
+ .quad 0x0080890000000000 /* TSS descriptor */
+ .quad 0x0000000000000000 /* TSS continued */
+SYM_DATA_END_LABEL(boot_gdt, SYM_L_LOCAL, boot_gdt_end)
+
#include "../../x86/xen/xen-head.S"

__PAGE_ALIGNED_BSS
--
2.17.1