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

diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
index 84b645cc8bc971d1acfa9539667f3d01f14b5fe3..5c2fd05bd52ce4845ad83cc7ba7552698327de43 100644 (file)
--- 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 cbb71c1b574f2d6ff22585e8a69bfa3aae643298..8c82be44be94100244d6173fce78b90a26029178 100644 (file)
--- 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 16da4ac015971c477054d7a91c68d79cb40458df..2b2e9162722188f5a0b0731cb1281ca7b8eadac6 100644 (file)
--- 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