Commit 5c3a85f3 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Borislav Petkov
Browse files

x86/boot/compressed: Move bootargs parsing out of 32-bit startup code 



Move the logic that chooses between the different EFI entrypoints out of
the 32-bit boot path, and into a 64-bit helper that can perform the same
task much more cleanly. While at it, document the mixed mode boot flow
in a code comment.

Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20221122161017.2426828-4-ardb@kernel.org
parent e2ab9eab

arch/x86/boot/compressed/efi_mixed.S

+43 −0
Original line number Diff line number Diff line
@@ -22,6 +22,49 @@ 


	.code64

	.text

/*

 * When booting in 64-bit mode on 32-bit EFI firmware, startup_64_mixed_mode()

 * is the first thing that runs after switching to long mode. Depending on

 * whether the EFI handover protocol or the compat entry point was used to

 * enter the kernel, it will either branch to the 64-bit EFI handover

 * entrypoint at offset 0x390 in the image, or to the 64-bit EFI PE/COFF

 * entrypoint efi_pe_entry(). In the former case, the bootloader must provide a

 * struct bootparams pointer as the third argument, so the presence of such a

 * pointer is used to disambiguate.

 *

 *                                                             +--------------+

 *  +------------------+     +------------+            +------>| efi_pe_entry |

 *  | efi32_pe_entry   |---->|            |            |       +-----------+--+

 *  +------------------+     |            |     +------+----------------+  |

 *                           | startup_32 |---->| startup_64_mixed_mode |  |

 *  +------------------+     |            |     +------+----------------+  V

 *  | efi32_stub_entry |---->|            |            |     +------------------+

 *  +------------------+     +------------+            +---->| efi64_stub_entry |

 *                                                           +-------------+----+

 *                           +------------+     +----------+               |

 *                           | startup_64 |<----| efi_main |<--------------+

 *                           +------------+     +----------+

 */

SYM_FUNC_START(startup_64_mixed_mode)

	lea	efi32_boot_args(%rip), %rdx

	mov	0(%rdx), %edi

	mov	4(%rdx), %esi

	mov	8(%rdx), %edx		// saved bootparams pointer

	test	%edx, %edx

	jnz	efi64_stub_entry

	/*

	 * 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.

	 */

	sub	$40, %rsp

	mov	%rdi, %rcx		// MS calling convention

	mov	%rsi, %rdx

	jmp	efi_pe_entry

SYM_FUNC_END(startup_64_mixed_mode)



SYM_FUNC_START(__efi64_thunk)

	push	%rbp

	push	%rbx

arch/x86/boot/compressed/head_64.S

+4 −20
Original line number Diff line number Diff line
@@ -261,25 +261,9 @@ SYM_FUNC_START(startup_32) 
	 */

	leal	rva(startup_64)(%ebp), %eax

#ifdef CONFIG_EFI_MIXED

	movl	rva(efi32_boot_args)(%ebp), %edi

	testl	%edi, %edi

	jz	1f

	leal	rva(efi64_stub_entry)(%ebp), %eax

	movl	rva(efi32_boot_args+4)(%ebp), %esi

	movl	rva(efi32_boot_args+8)(%ebp), %edx	// saved bootparams pointer

	testl	%edx, %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	rva(efi_pe_entry)(%ebp), %eax

	movl	%edi, %ecx			// MS calling convention

	movl	%esi, %edx

	cmpb	$1, rva(efi_is64)(%ebp)

	je	1f

	leal	rva(startup_64_mixed_mode)(%ebp), %eax

1:

#endif

	/* Check if the C-bit position is correct when SEV is active */
@@ -779,7 +763,7 @@ SYM_DATA_END_LABEL(boot32_idt, SYM_L_GLOBAL, boot32_idt_end) 
SYM_DATA(image_offset, .long 0)

#endif

#ifdef CONFIG_EFI_MIXED

SYM_DATA_LOCAL(efi32_boot_args, .long 0, 0, 0)

SYM_DATA(efi32_boot_args, .long 0, 0, 0)

SYM_DATA(efi_is64, .byte 1)



#define ST32_boottime		60 // offsetof(efi_system_table_32_t, boottime)