[tip: x86/seves] x86/head/64: Install startup GDT

["tip-bot2 for Joerg Roedel" <tip-bot2@linutronix.de>]

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

Commit-ID:     866b556efa1295934ed0bc20c2f208c93a873fb0
Gitweb:        https://git.kernel.org/tip/866b556efa1295934ed0bc20c2f208c93a873fb0
Author:        Joerg Roedel <jroedel@suse.de>
AuthorDate:    Mon, 07 Sep 2020 15:15:30 +02:00
Committer:     Borislav Petkov <bp@suse.de>
CommitterDate: Mon, 07 Sep 2020 21:33:17 +02:00

x86/head/64: Install startup GDT

Handling exceptions during boot requires a working GDT. The kernel GDT
can't be used on the direct mapping, so load a startup GDT and setup
segments.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-30-joro@8bytes.org
---
 arch/x86/include/asm/setup.h |  1 +
 arch/x86/kernel/head64.c     | 33 +++++++++++++++++++++++++++++++++
 arch/x86/kernel/head_64.S    | 14 ++++++++++++++
 3 files changed, 48 insertions(+)

diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
index 84b645c..5c2fd05 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -48,6 +48,7 @@ extern void reserve_standard_io_resources(void);
 extern void i386_reserve_resources(void);
 extern unsigned long __startup_64(unsigned long physaddr, struct boot_params *bp);
 extern unsigned long __startup_secondary_64(void);
+extern void startup_64_setup_env(unsigned long physbase);
 extern int early_make_pgtable(unsigned long address);
 
 #ifdef CONFIG_X86_INTEL_MID
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index cbb71c1..8c82be4 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -61,6 +61,24 @@ 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] = {
+	[GDT_ENTRY_KERNEL32_CS]         = GDT_ENTRY_INIT(0xc09b, 0, 0xfffff),
+	[GDT_ENTRY_KERNEL_CS]           = GDT_ENTRY_INIT(0xa09b, 0, 0xfffff),
+	[GDT_ENTRY_KERNEL_DS]           = GDT_ENTRY_INIT(0xc093, 0, 0xfffff),
+};
+
+/*
+ * Address needs to be set at runtime because it references the startup_gdt
+ * while the kernel still uses a direct mapping.
+ */
+static struct desc_ptr startup_gdt_descr = {
+	.size = sizeof(startup_gdt),
+	.address = 0,
+};
+
 #define __head	__section(.head.text)
 
 static void __head *fixup_pointer(void *ptr, unsigned long physaddr)
@@ -489,3 +507,18 @@ void __init x86_64_start_reservations(char *real_mode_data)
 
 	start_kernel();
 }
+
+/*
+ * Setup boot CPU state needed before kernel switches to virtual addresses.
+ */
+void __head startup_64_setup_env(unsigned long physbase)
+{
+	/* Load GDT */
+	startup_gdt_descr.address = (unsigned long)fixup_pointer(startup_gdt, physbase);
+	native_load_gdt(&startup_gdt_descr);
+
+	/* New GDT is live - reload data segment registers */
+	asm volatile("movl %%eax, %%ds\n"
+		     "movl %%eax, %%ss\n"
+		     "movl %%eax, %%es\n" : : "a"(__KERNEL_DS) : "memory");
+}
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 16da4ac..2b2e916 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -73,6 +73,20 @@ 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
 
+	leaq	_text(%rip), %rdi
+	pushq	%rsi
+	call	startup_64_setup_env
+	popq	%rsi
+
+	/* 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