Commit 866b556e authored by Joerg Roedel's avatar Joerg Roedel Committed by Borislav Petkov
Browse files

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: default avatarJoerg Roedel <jroedel@suse.de>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-30-joro@8bytes.org
parent 4bed2266

arch/x86/include/asm/setup.h

+1 −0
Original line number Diff line number Diff line
@@ -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

arch/x86/kernel/head64.c

+33 −0
Original line number Diff line number Diff line
@@ -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");

}

arch/x86/kernel/head_64.S

+14 −0
Original line number Diff line number Diff line
@@ -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

CRA Git | Maintained and supported by SUSTech CRA and CCSE