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@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: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/boot/compressed/efi_thunk_64.S b/arch/x86/boot/compressed/efi_thunk_64.S
index 593913692d166d7146690d07520db75b45fb7d31..6d95eb6b8912594d7ced575f1454f30d185354f7 100644 (file)
--- 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 */