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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: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20221122161017.2426828-4-ardb@kernel.org
This commit is contained in:
Ard Biesheuvel 2022-11-22 17:10:03 +01:00 committed by Borislav Petkov
parent e2ab9eab32
commit 5c3a85f35b
2 changed files with 47 additions and 20 deletions
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43
arch/x86/boot/compressed/efi_mixed.S
View File

@ -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

24
arch/x86/boot/compressed/head_64.S
View File

@ -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)