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efi/libstub/x86: Use mandatory 16-byte stack alignment in mixed mode

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Reduce the stack frame of the EFI stub's mixed mode thunk routine by
8 bytes, by moving the GDT and return addresses to EBP and EBX, which
we need to preserve anyway, since their top halves will be cleared by
the call into 32-bit firmware code. Doing so results in the UEFI code
being entered with a 16 byte aligned stack, as mandated by the UEFI
spec, fixing the last occurrence in the 64-bit kernel where we violate
this requirement.

Also, move the saved GDT from a global variable to an unused part of the
stack frame, and touch up some other parts of the code.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200113172245.27925-3-ardb@kernel.org
This commit is contained in:
Ard Biesheuvel 2020-01-13 18:22:34 +01:00 committed by Ingo Molnar
parent 796eb8d26a
commit ac3c76cc6d
1 changed files with 13 additions and 33 deletions
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46
arch/x86/boot/compressed/efi_thunk_64.S
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@ -27,12 +27,9 @@ SYM_FUNC_START(__efi64_thunk)
push %rbp
push %rbx
subq $8, %rsp
leaq 1f(%rip), %rax
movl %eax, 4(%rsp)
leaq efi_gdt64(%rip), %rax
movl %eax, (%rsp)
movl %eax, 2(%rax) /* Fixup the gdt base address */
leaq 1f(%rip), %rbp
leaq efi_gdt64(%rip), %rbx
movl %ebx, 2(%rbx) /* Fixup the gdt base address */
movl %ds, %eax
push %rax
@ -48,12 +45,10 @@ SYM_FUNC_START(__efi64_thunk)
movl %esi, 0x0(%rsp)
movl %edx, 0x4(%rsp)
movl %ecx, 0x8(%rsp)
movq %r8, %rsi
movl %esi, 0xc(%rsp)
movq %r9, %rsi
movl %esi, 0x10(%rsp)
movl %r8d, 0xc(%rsp)
movl %r9d, 0x10(%rsp)
sgdt save_gdt(%rip)
sgdt 0x14(%rsp)
/*
* Switch to gdt with 32-bit segments. This is the firmware GDT
@ -68,11 +63,10 @@ SYM_FUNC_START(__efi64_thunk)
pushq %rax
lretq
1: addq $32, %rsp
1: lgdt 0x14(%rsp)
addq $32, %rsp
movq %rdi, %rax
lgdt save_gdt(%rip)
pop %rbx
movl %ebx, %ss
pop %rbx
@ -83,15 +77,9 @@ SYM_FUNC_START(__efi64_thunk)
/*
* Convert 32-bit status code into 64-bit.
*/
test %rax, %rax
jz 1f
movl %eax, %ecx
andl $0x0fffffff, %ecx
andl $0xf0000000, %eax
shl $32, %rax
or %rcx, %rax
1:
addq $8, %rsp
roll $1, %eax
rorq $1, %rax
pop %rbx
pop %rbp
ret
@ -135,9 +123,7 @@ SYM_FUNC_START_LOCAL(efi_enter32)
*/
cli
movl 56(%esp), %eax
movl %eax, 2(%eax)
lgdtl (%eax)
lgdtl (%ebx)
movl %cr4, %eax
btsl $(X86_CR4_PAE_BIT), %eax
@ -154,9 +140,8 @@ SYM_FUNC_START_LOCAL(efi_enter32)
xorl %eax, %eax
lldt %ax
movl 60(%esp), %eax
pushl $__KERNEL_CS
pushl %eax
pushl %ebp
/* Enable paging */
movl %cr0, %eax
@ -172,11 +157,6 @@ SYM_DATA_START(efi32_boot_gdt)
.quad 0
SYM_DATA_END(efi32_boot_gdt)
SYM_DATA_START_LOCAL(save_gdt)
.word 0
.quad 0
SYM_DATA_END(save_gdt)
SYM_DATA_START(efi_gdt64)
.word efi_gdt64_end - efi_gdt64
.long 0 /* Filled out by user */