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x86/efi: Preserve segment registers in mixed mode

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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>
This commit is contained in:
Matt Fleming 2014-03-13 14:58:42 +00:00
parent 617b3c37da
commit e10848a26a
1 changed files with 17 additions and 8 deletions
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25
arch/x86/platform/efi/efi_stub_64.S
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@ -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