Commit ef5a7b5e authored by Arvind Sankar's avatar Arvind Sankar Committed by Ard Biesheuvel
Browse files

efi/x86: Remove GDT setup from efi_main 



The 64-bit kernel will already load a GDT in startup_64, which is the
next function to execute after return from efi_main.

Add GDT setup code to the 32-bit kernel's startup_32 as well. Doing it
in the head code has the advantage that we can avoid potentially
corrupting the GDT during copy/decompression. This also removes
dependence on having a specific GDT layout setup by the bootloader.

Both startup_32 and startup_64 now clear interrupts on entry, so we can
remove that from efi_main as well.

Signed-off-by: default avatarArvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200202171353.3736319-6-nivedita@alum.mit.edu


Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
parent cae0e431

arch/x86/boot/compressed/eboot.c

+0 −103
Original line number Diff line number Diff line
@@ -712,10 +712,8 @@ struct boot_params *efi_main(efi_handle_t handle, 
			     efi_system_table_t *sys_table_arg,

			     struct boot_params *boot_params)

{

	struct desc_ptr *gdt = NULL;

	struct setup_header *hdr = &boot_params->hdr;

	efi_status_t status;

	struct desc_struct *desc;

	unsigned long cmdline_paddr;



	sys_table = sys_table_arg;
@@ -753,20 +751,6 @@ struct boot_params *efi_main(efi_handle_t handle, 


	setup_quirks(boot_params);



	status = efi_bs_call(allocate_pool, EFI_LOADER_DATA, sizeof(*gdt),

			     (void **)&gdt);

	if (status != EFI_SUCCESS) {

		efi_printk("Failed to allocate memory for 'gdt' structure\n");

		goto fail;

	}



	gdt->size = 0x800;

	status = efi_low_alloc(gdt->size, 8, (unsigned long *)&gdt->address);

	if (status != EFI_SUCCESS) {

		efi_printk("Failed to allocate memory for 'gdt'\n");

		goto fail;

	}



	/*

	 * If the kernel isn't already loaded at the preferred load

	 * address, relocate it.
@@ -793,93 +777,6 @@ struct boot_params *efi_main(efi_handle_t handle, 
		goto fail;

	}



	memset((char *)gdt->address, 0x0, gdt->size);

	desc = (struct desc_struct *)gdt->address;



	/* The first GDT is a dummy. */

	desc++;



	if (IS_ENABLED(CONFIG_X86_64)) {

		/* __KERNEL32_CS */

		desc->limit0	= 0xffff;

		desc->base0	= 0x0000;

		desc->base1	= 0x0000;

		desc->type	= SEG_TYPE_CODE | SEG_TYPE_EXEC_READ;

		desc->s		= DESC_TYPE_CODE_DATA;

		desc->dpl	= 0;

		desc->p		= 1;

		desc->limit1	= 0xf;

		desc->avl	= 0;

		desc->l		= 0;

		desc->d		= SEG_OP_SIZE_32BIT;

		desc->g		= SEG_GRANULARITY_4KB;

		desc->base2	= 0x00;



		desc++;

	} else {

		/* Second entry is unused on 32-bit */

		desc++;

	}



	/* __KERNEL_CS */

	desc->limit0	= 0xffff;

	desc->base0	= 0x0000;

	desc->base1	= 0x0000;

	desc->type	= SEG_TYPE_CODE | SEG_TYPE_EXEC_READ;

	desc->s		= DESC_TYPE_CODE_DATA;

	desc->dpl	= 0;

	desc->p		= 1;

	desc->limit1	= 0xf;

	desc->avl	= 0;



	if (IS_ENABLED(CONFIG_X86_64)) {

		desc->l = 1;

		desc->d = 0;

	} else {

		desc->l = 0;

		desc->d = SEG_OP_SIZE_32BIT;

	}

	desc->g		= SEG_GRANULARITY_4KB;

	desc->base2	= 0x00;

	desc++;



	/* __KERNEL_DS */

	desc->limit0	= 0xffff;

	desc->base0	= 0x0000;

	desc->base1	= 0x0000;

	desc->type	= SEG_TYPE_DATA | SEG_TYPE_READ_WRITE;

	desc->s		= DESC_TYPE_CODE_DATA;

	desc->dpl	= 0;

	desc->p		= 1;

	desc->limit1	= 0xf;

	desc->avl	= 0;

	desc->l		= 0;

	desc->d		= SEG_OP_SIZE_32BIT;

	desc->g		= SEG_GRANULARITY_4KB;

	desc->base2	= 0x00;

	desc++;



	if (IS_ENABLED(CONFIG_X86_64)) {

		/* Task segment value */

		desc->limit0	= 0x0000;

		desc->base0	= 0x0000;

		desc->base1	= 0x0000;

		desc->type	= SEG_TYPE_TSS;

		desc->s		= 0;

		desc->dpl	= 0;

		desc->p		= 1;

		desc->limit1	= 0x0;

		desc->avl	= 0;

		desc->l		= 0;

		desc->d		= 0;

		desc->g		= SEG_GRANULARITY_4KB;

		desc->base2	= 0x00;

		desc++;

	}



	asm volatile("cli");

	asm volatile ("lgdt %0" : : "m" (*gdt));



	return boot_params;

fail:

	efi_printk("efi_main() failed!\n");

arch/x86/boot/compressed/head_32.S

+34 −6
Original line number Diff line number Diff line
@@ -64,12 +64,6 @@ 
SYM_FUNC_START(startup_32)

	cld

	cli

	movl	$__BOOT_DS, %eax

	movl	%eax, %ds

	movl	%eax, %es

	movl	%eax, %fs

	movl	%eax, %gs

	movl	%eax, %ss



/*

 * Calculate the delta between where we were compiled to run
@@ -84,6 +78,19 @@ SYM_FUNC_START(startup_32) 
1:	popl	%ebp

	subl	$1b, %ebp



	/* Load new GDT */

	leal	gdt(%ebp), %eax

	movl	%eax, 2(%eax)

	lgdt	(%eax)



	/* Load segment registers with our descriptors */

	movl	$__BOOT_DS, %eax

	movl	%eax, %ds

	movl	%eax, %es

	movl	%eax, %fs

	movl	%eax, %gs

	movl	%eax, %ss



/*

 * %ebp contains the address we are loaded at by the boot loader and %ebx

 * contains the address where we should move the kernel image temporarily
@@ -129,6 +136,16 @@ SYM_FUNC_START(startup_32) 
	cld

	popl	%esi



	/*

	 * The GDT may get overwritten either during the copy we just did or

	 * during extract_kernel below. To avoid any issues, repoint the GDTR

	 * to the new copy of the GDT. EAX still contains the previously

	 * calculated relocation offset of init_size - _end.

	 */

	leal	gdt(%ebx), %edx

	addl	%eax, 2(%edx)

	lgdt	(%edx)



/*

 * Jump to the relocated address.

 */
@@ -201,6 +218,17 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) 
	jmp	*%eax

SYM_FUNC_END(.Lrelocated)



	.data

	.balign	8

SYM_DATA_START_LOCAL(gdt)

	.word	gdt_end - gdt - 1

	.long	0

	.word	0

	.quad	0x0000000000000000	/* Reserved */

	.quad	0x00cf9a000000ffff	/* __KERNEL_CS */

	.quad	0x00cf92000000ffff	/* __KERNEL_DS */

SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end)



/*

 * Stack and heap for uncompression

 */

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