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Subject[PATCH 25/25] efi/libstub/x86: avoid globals to store context during mixed mode calls
Date
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@kernel.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
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