[tip: x86/boot] x86/boot/64: Load the final kernel GDT during early boot directly, remove startup_gdt[]

tip-bot2 for Brian Gerst
2024-02-28T10:11:29Z

The following commit has been merged into the x86/boot branch of tip:

Commit-ID: 11e36b0f7c2150a6453872b79555767b43c846d0
Gitweb: https://git.kernel.org/tip/11e36b0f7c2150a6453872b79555767b43c846d0
Author: Brian Gerst <brgerst@gmail.com>
AuthorDate: Mon, 26 Feb 2024 17:05:44 -05:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 28 Feb 2024 11:02:16 +01:00

x86/boot/64: Load the final kernel GDT during early boot directly, remove startup_gdt[]

Instead of loading a duplicate GDT just for early boot, load the kernel
GDT from its physical address.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20240226220544.70769-1-brgerst@gmail.com
---
arch/x86/include/asm/desc.h | 1 +
arch/x86/kernel/head64.c | 13 ++-----------
2 files changed, 3 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
index ab97b22..52c0150 100644
--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -46,6 +46,7 @@ struct gdt_page {
} __attribute__((aligned(PAGE_SIZE)));

DECLARE_PER_CPU_PAGE_ALIGNED(struct gdt_page, gdt_page);
+DECLARE_INIT_PER_CPU(gdt_page);

/* Provide the original GDT */
static inline struct desc_struct *get_cpu_gdt_rw(unsigned int cpu)
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 72351c3..fd77a26 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -68,15 +68,6 @@ unsigned long vmemmap_base __ro_after_init = __VMEMMAP_BASE_L4;
EXPORT_SYMBOL(vmemmap_base);
#endif

-/*
- * GDT used on the boot CPU before switching to virtual addresses.
- */
-static struct desc_struct startup_gdt[GDT_ENTRIES] __initdata = {
- [GDT_ENTRY_KERNEL32_CS] = GDT_ENTRY_INIT(DESC_CODE32, 0, 0xfffff),
- [GDT_ENTRY_KERNEL_CS] = GDT_ENTRY_INIT(DESC_CODE64, 0, 0xfffff),
- [GDT_ENTRY_KERNEL_DS] = GDT_ENTRY_INIT(DESC_DATA64, 0, 0xfffff),
-};
-
#ifdef CONFIG_X86_5LEVEL
static void __head *fixup_pointer(void *ptr, unsigned long physaddr)
{
@@ -589,8 +580,8 @@ void __head startup_64_setup_gdt_idt(void)
void *handler = NULL;

struct desc_ptr startup_gdt_descr = {
- .address = (unsigned long)&RIP_REL_REF(startup_gdt),
- .size = sizeof(startup_gdt) - 1,
+ .address = (unsigned long)&RIP_REL_REF(init_per_cpu_var(gdt_page.gdt)),
+ .size = GDT_SIZE - 1,
};

/* Load GDT */