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x86/head/64: Install startup GDT

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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
This commit is contained in:
Joerg Roedel 2020-09-07 15:15:30 +02:00 committed by Borislav Petkov
parent 4bed2266cc
commit 866b556efa
3 changed files with 48 additions and 0 deletions
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1
arch/x86/include/asm/setup.h
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@ -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

33
arch/x86/kernel/head64.c
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@ -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");
}

14
arch/x86/kernel/head_64.S
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@ -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