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: Matt Fleming <matt.fleming@intel.com>
diff --git a/arch/x86/platform/efi/efi_stub_64.S b/arch/x86/platform/efi/efi_stub_64.S
index 65b787a..e0984ef 100644
--- a/arch/x86/platform/efi/efi_stub_64.S
+++ b/arch/x86/platform/efi/efi_stub_64.S
@@ -176,6 +176,13 @@
* 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 @@
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 @@
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 @@
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 @@
*/
cli
- movl 44(%esp), %eax
+ movl 68(%esp), %eax
movl %eax, 2(%eax)
lgdtl (%eax)
@@ -286,7 +295,7 @@
xorl %eax, %eax
lldt %ax
- movl 48(%esp), %eax
+ movl 72(%esp), %eax
pushl $__KERNEL_CS
pushl %eax