linux-kernel - [PATCH 25/25] efi/libstub/x86: avoid globals to store context during mixed mode calls

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Message-Id: <20191224151025.32482-26-ardb@kernel.org>
Date:   Tue, 24 Dec 2019 16:10:25 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-efi@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Ard Biesheuvel <ardb@...nel.org>, linux-kernel@...r.kernel.org,
        Arvind Sankar <nivedita@...m.mit.edu>
Subject: [PATCH 25/25] 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: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/boot/compressed/efi_thunk_64.S | 17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)

diff --git a/arch/x86/boot/compressed/efi_thunk_64.S b/arch/x86/boot/compressed/efi_thunk_64.S
index 593913692d16..6d95eb6b8912 100644
--- a/arch/x86/boot/compressed/efi_thunk_64.S
+++ b/arch/x86/boot/compressed/efi_thunk_64.S
@@ -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 */
-- 
2.20.1