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Commit e10848a2 authored by Matt Fleming's avatar Matt Fleming
Browse files

x86/efi: Preserve segment registers in mixed mode 



I was triggering a #GP(0) from userland when running with
CONFIG_EFI_MIXED and CONFIG_IA32_EMULATION, from what looked like
register corruption. Turns out that the mixed mode code was trashing the
contents of %ds, %es and %ss in __efi64_thunk().

Save and restore the contents of these segment registers across the call
to __efi64_thunk() so that we don't corrupt the CPU context.

Signed-off-by: default avatarMatt Fleming <matt.fleming@intel.com>
parent 617b3c37

arch/x86/platform/efi/efi_stub_64.S

+17 −8
Original line number Diff line number Diff line
@@ -176,6 +176,13 @@ ENDPROC(efi_call6) 
 * This function must be invoked with a 1:1 mapped stack.

 */

ENTRY(__efi64_thunk)

	movl	%ds, %eax

	push	%rax

	movl	%es, %eax

	push	%rax

	movl	%ss, %eax

	push	%rax



	subq	$32, %rsp

	movl	%esi, 0x0(%rsp)

	movl	%edx, 0x4(%rsp)
@@ -191,7 +198,7 @@ ENTRY(__efi64_thunk) 
	movq	%rbx, func_rt_ptr(%rip)



	/* Switch to gdt with 32-bit segments */

	movl	40(%rsp), %eax

	movl	64(%rsp), %eax

	lgdt	(%rax)



	leaq	efi_enter32(%rip), %rax
@@ -203,6 +210,13 @@ ENTRY(__efi64_thunk) 


	lgdt	save_gdt(%rip)



	pop	%rbx

	movl	%ebx, %ss

	pop	%rbx

	movl	%ebx, %es

	pop	%rbx

	movl	%ebx, %ds



	/*

	 * Convert 32-bit status code into 64-bit.

	 */
@@ -218,11 +232,6 @@ ENTRY(__efi64_thunk) 
ENDPROC(__efi64_thunk)



ENTRY(efi_exit32)

	xorq	%rax, %rax

	movl	%eax, %ds

	movl	%eax, %es

	movl	%eax, %ss



	movq	func_rt_ptr(%rip), %rax

	push	%rax

	mov	%rdi, %rax
@@ -267,7 +276,7 @@ ENTRY(efi_enter32) 
	 */

	cli



	movl	44(%esp), %eax

	movl	68(%esp), %eax

	movl	%eax, 2(%eax)

	lgdtl	(%eax)
@@ -286,7 +295,7 @@ ENTRY(efi_enter32) 
	xorl	%eax, %eax

	lldt	%ax



	movl	48(%esp), %eax

	movl	72(%esp), %eax

	pushl	$__KERNEL_CS

	pushl	%eax