Commit 6e2da8d8 authored by Ard Biesheuvel's avatar Ard Biesheuvel
Browse files

x86/efi/mixed: Remove dependency on legacy startup_32 code 



The EFI mixed mode startup code calls into startup_32 in the legacy
decompressor with a mocked up boot_params struct, only to get it to set
up the 1:1 mapping of the lower 4 GiB of memory and switch to a GDT that
supports 64-bit mode.

In order to be able to reuse the EFI mixed mode startup code in EFI
zboot images, which do not incorporate the legacy decompressor code,
decouple it, by dealing with the GDT and IDT directly.

Doing so makes it possible to construct a GDT that is compatible with
the one the firmware uses, with one additional entry for a 64-bit mode
code segment appended. This removes the need entirely to switch between
GDTs and IDTs or data segment selector values and all of this code can
be removed.

Acked-by: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
parent d545e182

arch/x86/boot/compressed/efi_mixed.S

+65 −162
Original line number Diff line number Diff line
@@ -15,70 +15,23 @@ 
 */



#include <linux/linkage.h>

#include <asm/asm-offsets.h>

#include <asm/desc_defs.h>

#include <asm/msr.h>

#include <asm/page_types.h>

#include <asm/pgtable_types.h>

#include <asm/processor-flags.h>

#include <asm/segment.h>

#include <asm/setup.h>



	.code64

	.text

/*

 * When booting in 64-bit mode on 32-bit EFI firmware, startup_64_mixed_mode()

 * is the first thing that runs after switching to long mode. Depending on

 * whether the EFI handover protocol or the compat entry point was used to

 * enter the kernel, it will either branch to the common 64-bit EFI stub

 * entrypoint efi_stub_entry() directly, or via the 64-bit EFI PE/COFF

 * entrypoint efi_pe_entry(). In the former case, the bootloader must provide a

 * struct bootparams pointer as the third argument, so the presence of such a

 * pointer is used to disambiguate.

 *

 *                                                             +--------------+

 *  +------------------+     +------------+            +------>| efi_pe_entry |

 *  | efi32_pe_entry   |---->|            |            |       +-----------+--+

 *  +------------------+     |            |     +------+----------------+  |

 *                           | startup_32 |---->| startup_64_mixed_mode |  |

 *  +------------------+     |            |     +------+----------------+  |

 *  | efi32_stub_entry |---->|            |            |                   |

 *  +------------------+     +------------+            |                   |

 *                                                     V                   |

 *                           +------------+     +----------------+         |

 *                           | startup_64 |<----| efi_stub_entry |<--------+

 *                           +------------+     +----------------+

 */

SYM_FUNC_START(startup_64_mixed_mode)

	lea	efi32_boot_args(%rip), %rdx

	mov	0(%rdx), %edi

	mov	4(%rdx), %esi



	leaq	(pte + 5 * PAGE_SIZE)(%rip), %rax

	movq	%rax, %cr3		// reload after startup_32



	/* Switch to the firmware's stack */

	movl	efi32_boot_sp(%rip), %esp

	andl	$~7, %esp



	mov	8(%rdx), %edx		// saved bootparams pointer

	call	efi_stub_entry

SYM_FUNC_END(startup_64_mixed_mode)



SYM_FUNC_START(__efi64_thunk)

	push	%rbp

	push	%rbx



	movl	%ds, %eax

	push	%rax

	movl	%es, %eax

	push	%rax

	movl	%ss, %eax

	push	%rax



	/* Copy args passed on stack */

	movq	0x30(%rsp), %rbp

	movq	0x38(%rsp), %rbx

	movq	0x40(%rsp), %rax

	movq	0x18(%rsp), %rbp

	movq	0x20(%rsp), %rbx

	movq	0x28(%rsp), %rax



	/*

	 * Convert x86-64 ABI params to i386 ABI
@@ -93,44 +46,14 @@ SYM_FUNC_START(__efi64_thunk) 
	movl	%ebx, 0x18(%rsp)

	movl	%eax, 0x1c(%rsp)



	leaq	0x20(%rsp), %rbx

	sgdt	(%rbx)

	sidt	16(%rbx)



	leaq	1f(%rip), %rbp

	movl	%cs, %ebx



	/*

	 * Switch to IDT and GDT with 32-bit segments. These are the firmware

	 * GDT and IDT that were installed when the kernel started executing.

	 * The pointers were saved by the efi32_entry() routine below.

	 *

	 * Pass the saved DS selector to the 32-bit code, and use far return to

	 * restore the saved CS selector.

	 */

	lidt	efi32_boot_idt(%rip)

	lgdt	efi32_boot_gdt(%rip)



	movzwl	efi32_boot_ds(%rip), %edx

	movzwq	efi32_boot_cs(%rip), %rax

	pushq	%rax

	leaq	efi_enter32(%rip), %rax

	pushq	%rax

	lretq

	ljmpl	*efi32_call(%rip)



1:	addq	$64, %rsp

	movq	%rdi, %rax



	pop	%rbx

	movl	%ebx, %ss

	pop	%rbx

	movl	%ebx, %es

	pop	%rbx

	movl	%ebx, %ds

	/* Clear out 32-bit selector from FS and GS */

	xorl	%ebx, %ebx

	movl	%ebx, %fs

	movl	%ebx, %gs



	pop	%rbx

	pop	%rbp

	RET
@@ -141,7 +64,6 @@ SYM_FUNC_END(__efi64_thunk) 
SYM_FUNC_START(efi32_stub_entry)

	call	1f

1:	popl	%ecx

	leal	(efi32_boot_args - 1b)(%ecx), %ebx



	/* Clear BSS */

	xorl	%eax, %eax
@@ -153,11 +75,8 @@ SYM_FUNC_START(efi32_stub_entry) 
	rep	stosl



	add	$0x4, %esp		/* Discard return address */

	popl	%ecx

	popl	%edx

	popl	%esi

	movl	%esi, 8(%ebx)

	jmp	efi32_entry

	movl	8(%esp), %ebx		/* struct boot_params pointer */

	jmp	efi32_startup

SYM_FUNC_END(efi32_stub_entry)

#endif
@@ -167,13 +86,6 @@ SYM_FUNC_END(efi32_stub_entry) 
 * The stack should represent the 32-bit calling convention.

 */

SYM_FUNC_START_LOCAL(efi_enter32)

	/* Load firmware selector into data and stack segment registers */

	movl	%edx, %ds

	movl	%edx, %es

	movl	%edx, %fs

	movl	%edx, %gs

	movl	%edx, %ss



	/* Disable paging */

	movl	%cr0, %eax

	btrl	$X86_CR0_PG_BIT, %eax
@@ -190,21 +102,9 @@ SYM_FUNC_START_LOCAL(efi_enter32) 
	/* We must preserve return value */

	movl	%eax, %edi



	/*

	 * Some firmware will return with interrupts enabled. Be sure to

	 * disable them before we switch GDTs and IDTs.

	 */

	cli



	lidtl	16(%ebx)

	lgdtl	(%ebx)



	xorl	%eax, %eax

	lldt	%ax



	call	efi32_enable_long_mode



	pushl	$__KERNEL_CS

	pushl	%ebx

	pushl	%ebp

	lret

SYM_FUNC_END(efi_enter32)
@@ -230,50 +130,56 @@ SYM_FUNC_START_LOCAL(efi32_enable_long_mode) 
SYM_FUNC_END(efi32_enable_long_mode)



/*

 * This is the common EFI stub entry point for mixed mode.

 * This is the common EFI stub entry point for mixed mode. It sets up the GDT

 * and page tables needed for 64-bit execution, after which it calls the

 * common 64-bit EFI entrypoint efi_stub_entry().

 *

 * Arguments:	%ecx	image handle

 * 		%edx	EFI system table pointer

 * Arguments:	0(%esp)	image handle

 * 		4(%esp)	EFI system table pointer

 *		%ebx	struct boot_params pointer (or NULL)

 *

 * Since this is the point of no return for ordinary execution, no registers

 * are considered live except for the function parameters. [Note that the EFI

 * stub may still exit and return to the firmware using the Exit() EFI boot

 * service.]

 */

SYM_FUNC_START_LOCAL(efi32_entry)

	call	1f

1:	pop	%ebx



	/* Save firmware GDTR and code/data selectors */

	sgdtl	(efi32_boot_gdt - 1b)(%ebx)

	movw	%cs, (efi32_boot_cs - 1b)(%ebx)

	movw	%ds, (efi32_boot_ds - 1b)(%ebx)



	/* Store firmware IDT descriptor */

	sidtl	(efi32_boot_idt - 1b)(%ebx)



	/* Store firmware stack pointer */

	movl	%esp, (efi32_boot_sp - 1b)(%ebx)



	/* Store boot arguments */

	leal	(efi32_boot_args - 1b)(%ebx), %ebx

	movl	%ecx, 0(%ebx)

	movl	%edx, 4(%ebx)

	movb	$0x0, 12(%ebx)          // efi_is64



	/*

	 * Allocate some memory for a temporary struct boot_params, which only

	 * needs the minimal pieces that startup_32() relies on.

	 */

	subl	$PARAM_SIZE, %esp

	movl	%esp, %esi

	movl	$PAGE_SIZE, BP_kernel_alignment(%esi)

	movl	$_end - 1b, BP_init_size(%esi)

	subl	$startup_32 - 1b, BP_init_size(%esi)

SYM_FUNC_START_LOCAL(efi32_startup)

	movl	%esp, %ebp



	subl	$8, %esp

	sgdtl	(%esp)			/* Save GDT descriptor to the stack */

	movl	2(%esp), %esi		/* Existing GDT pointer */

	movzwl	(%esp), %ecx		/* Existing GDT limit */

	inc	%ecx			/* Existing GDT size */

	andl	$~7, %ecx		/* Ensure size is multiple of 8 */



	subl	%ecx, %esp		/* Allocate new GDT */

	andl	$~15, %esp		/* Realign the stack */

	movl	%esp, %edi		/* New GDT address */

	leal	7(%ecx), %eax		/* New GDT limit */

	pushw	%cx			/* Push 64-bit CS (for LJMP below) */

	pushl	%edi			/* Push new GDT address */

	pushw	%ax			/* Push new GDT limit */



	/* Copy GDT to the stack and add a 64-bit code segment at the end */

	movl	$GDT_ENTRY(DESC_CODE64, 0, 0xfffff) & 0xffffffff, (%edi,%ecx)

	movl	$GDT_ENTRY(DESC_CODE64, 0, 0xfffff) >> 32, 4(%edi,%ecx)

	shrl	$2, %ecx

	cld

	rep	movsl			/* Copy the firmware GDT */

	lgdtl	(%esp)			/* Switch to the new GDT */



	call	1f

1:	pop	%edi



	/* Record mixed mode entry */

	movb	$0x0, (efi_is64 - 1b)(%edi)



	/* Set up indirect far call to re-enter 32-bit mode */

	leal	(efi32_call - 1b)(%edi), %eax

	addl	%eax, (%eax)

	movw	%cs, 4(%eax)



	/* Disable paging */

	movl	%cr0, %eax

	btrl	$X86_CR0_PG_BIT, %eax
@@ -297,8 +203,17 @@ SYM_FUNC_START_LOCAL(efi32_entry) 
	movl	%edx, (%eax)

	movl	%eax, %cr3



	jmp	startup_32

SYM_FUNC_END(efi32_entry)

	call	efi32_enable_long_mode



	/* Set up far jump to 64-bit mode (CS is already on the stack) */

	leal	(efi_stub_entry - 1b)(%edi), %eax

	movl	%eax, 2(%esp)



	movl	0(%ebp), %edi

	movl	4(%ebp), %esi

	movl	%ebx, %edx

	ljmpl	*2(%esp)

SYM_FUNC_END(efi32_startup)



/*

 * efi_status_t efi32_pe_entry(efi_handle_t image_handle,
@@ -313,10 +228,8 @@ SYM_FUNC_START(efi32_pe_entry) 
	btl	$29, %edx			// check long mode bit

	jnc	1f

	leal	8(%esp), %esp			// preserve stack alignment

	movl	(%esp), %ecx			// image_handle

	movl	4(%esp), %edx			// sys_table

	jmp	efi32_entry			// pass %ecx, %edx

						// no other registers remain live

	xor	%ebx, %ebx			// no struct boot_params pointer

	jmp	efi32_startup			// only ESP and EBX remain live

1:	movl	$0x80000003, %eax		// EFI_UNSUPPORTED

	popl	%ebx

	RET
@@ -332,20 +245,10 @@ SYM_FUNC_END(efi64_stub_entry) 


	.data

	.balign	8

SYM_DATA_START_LOCAL(efi32_boot_gdt)

	.word	0

	.quad	0

SYM_DATA_END(efi32_boot_gdt)



SYM_DATA_START_LOCAL(efi32_boot_idt)

	.word	0

	.quad	0

SYM_DATA_END(efi32_boot_idt)



SYM_DATA_LOCAL(efi32_boot_cs, .word 0)

SYM_DATA_LOCAL(efi32_boot_ds, .word 0)

SYM_DATA_LOCAL(efi32_boot_sp, .long 0)

SYM_DATA_LOCAL(efi32_boot_args, .long 0, 0, 0)

SYM_DATA_START_LOCAL(efi32_call)

	.long	efi_enter32 - .

	.word	0x0

SYM_DATA_END(efi32_call)

SYM_DATA(efi_is64, .byte 1)



	.bss

arch/x86/boot/compressed/head_64.S

+0 −7
Original line number Diff line number Diff line
@@ -263,13 +263,6 @@ SYM_FUNC_START(startup_32) 
	 * used to perform that far jump.

	 */

	leal	rva(startup_64)(%ebp), %eax

#ifdef CONFIG_EFI_MIXED

	cmpb	$1, rva(efi_is64)(%ebp)

	je	1f

	leal	rva(startup_64_mixed_mode)(%ebp), %eax

1:

#endif



	pushl	$__KERNEL_CS

	pushl	%eax