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@xxxxxxxxxx> --- arch/x86/boot/compressed/efi_thunk_64.S | 46 +++++++------------------ 1 file changed, 13 insertions(+), 33 deletions(-) diff --git a/arch/x86/boot/compressed/efi_thunk_64.S b/arch/x86/boot/compressed/efi_thunk_64.S index d040ff5458e5..8fb7f6799c52 100644 --- a/arch/x86/boot/compressed/efi_thunk_64.S +++ b/arch/x86/boot/compressed/efi_thunk_64.S @@ -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 */ -- 2.20.1
