Commit 41d90b0c authored Jun 17, 2020 by Arvind Sankar Committed by Ard Biesheuvel Jun 17, 2020

efi/x86: Setup stack correctly for efi_pe_entry



Commit

  17054f49 ("efi/x86: Implement mixed mode boot without the handover protocol")

introduced a new entry point for the EFI stub to be booted in mixed mode
on 32-bit firmware.

When entered via efi32_pe_entry, control is first transferred to
startup_32 to setup for the switch to long mode, and then the EFI stub
proper is entered via efi_pe_entry. efi_pe_entry is an MS ABI function,
and the ABI requires 32 bytes of shadow stack space to be allocated by
the caller, as well as the stack being aligned to 8 mod 16 on entry.

Allocate 40 bytes on the stack before switching to 64-bit mode when
calling efi_pe_entry to account for this.

For robustness, explicitly align boot_stack_end to 16 bytes. It is
currently implicitly aligned since .bss is cacheline-size aligned,
head_64.o is the first object file with a .bss section, and the heap and
boot sizes are aligned.

Fixes: 17054f49 ("efi/x86: Implement mixed mode boot without the handover protocol")
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200617131957.2507632-1-nivedita@alum.mit.edu


Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

parent 435d1a47

arch/x86/boot/compressed/head_64.S

+10 −1

Original line number	Diff line number	Diff line
		@@ -213,7 +213,6 @@ SYM_FUNC_START(startup_32)
		* We place all of the values on our mini stack so lret can
		* used to perform that far jump.
		*/
		pushl $__KERNEL_CS
		leal startup_64(%ebp), %eax
		#ifdef CONFIG_EFI_MIXED
		movl efi32_boot_args(%ebp), %edi
		@@ -224,11 +223,20 @@ SYM_FUNC_START(startup_32)
		movl efi32_boot_args+8(%ebp), %edx // saved bootparams pointer
		cmpl $0, %edx
		jnz 1f
		/*
		* efi_pe_entry uses MS calling convention, which requires 32 bytes of
		* shadow space on the stack even if all arguments are passed in
		* registers. We also need an additional 8 bytes for the space that
		* would be occupied by the return address, and this also results in
		* the correct stack alignment for entry.
		*/
		subl $40, %esp
		leal efi_pe_entry(%ebp), %eax
		movl %edi, %ecx // MS calling convention
		movl %esi, %edx
		1:
		#endif
		pushl $__KERNEL_CS
		pushl %eax

		/* Enter paged protected Mode, activating Long Mode */
		@@ -784,6 +792,7 @@ SYM_DATA_LOCAL(boot_heap, .fill BOOT_HEAP_SIZE, 1, 0)

		SYM_DATA_START_LOCAL(boot_stack)
		.fill BOOT_STACK_SIZE, 1, 0
		.balign 16
		SYM_DATA_END_LABEL(boot_stack, SYM_L_LOCAL, boot_stack_end)

		/*

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