Commit 0679715e authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Ingo Molnar
Browse files

efi/libstub/x86: Avoid globals to store context during mixed mode calls 



Instead of storing the return address in a global variable when calling
a 32-bit EFI service from the 64-bit stub, avoid the indirection via
efi_exit32, and take the return address from the stack.

Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Cc: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Borislav Petkov <bp@alien8.de>
Cc: James Morse <james.morse@arm.com>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: https://lkml.kernel.org/r/20191224151025.32482-26-ardb@kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 7d4e323d

arch/x86/boot/compressed/efi_thunk_64.S

+3 −14
Original line number Diff line number Diff line
@@ -10,7 +10,7 @@ 
 * needs to be able to service interrupts.

 *

 * On the plus side, we don't have to worry about mangling 64-bit

 * addresses into 32-bits because we're executing with an identify

 * addresses into 32-bits because we're executing with an identity

 * mapped pagetable and haven't transitioned to 64-bit virtual addresses

 * yet.

 */
@@ -28,7 +28,7 @@ SYM_FUNC_START(efi64_thunk) 
	push	%rbx



	subq	$8, %rsp

	leaq	efi_exit32(%rip), %rax

	leaq	1f(%rip), %rax

	movl	%eax, 4(%rsp)

	leaq	efi_gdt64(%rip), %rax

	movl	%eax, (%rsp)
@@ -55,9 +55,6 @@ SYM_FUNC_START(efi64_thunk) 


	sgdt	save_gdt(%rip)



	leaq	1f(%rip), %rbx

	movq	%rbx, func_rt_ptr(%rip)



	/*

	 * Switch to gdt with 32-bit segments. This is the firmware GDT

	 * that was installed when the kernel started executing. This
@@ -72,6 +69,7 @@ SYM_FUNC_START(efi64_thunk) 
	lretq



1:	addq	$32, %rsp

	movq	%rdi, %rax



	lgdt	save_gdt(%rip)
@@ -99,13 +97,6 @@ SYM_FUNC_START(efi64_thunk) 
	ret

SYM_FUNC_END(efi64_thunk)



SYM_FUNC_START_LOCAL(efi_exit32)

	movq	func_rt_ptr(%rip), %rax

	push	%rax

	mov	%rdi, %rax

	ret

SYM_FUNC_END(efi_exit32)



	.code32

/*

 * EFI service pointer must be in %edi.
@@ -186,8 +177,6 @@ SYM_DATA_START_LOCAL(save_gdt) 
	.quad	0

SYM_DATA_END(save_gdt)



SYM_DATA_LOCAL(func_rt_ptr, .quad 0)



SYM_DATA_START(efi_gdt64)

	.word	efi_gdt64_end - efi_gdt64

	.long	0			/* Filled out by user */

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