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x86/efistub: Simplify and clean up handover entry code

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Now that the EFI entry code in assembler is only used by the optional
and deprecated EFI handover protocol, and given that the EFI stub C code
no longer returns to it, most of it can simply be dropped.

While at it, clarify the symbol naming, by merging efi_main() and
efi_stub_entry(), making the latter the shared entry point for all
different boot modes that enter via the EFI stub.

The efi32_stub_entry() and efi64_stub_entry() names are referenced
explicitly by the tooling that populates the setup header, so these must
be retained, but can be emitted as aliases of efi_stub_entry() where
appropriate.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230807162720.545787-5-ardb@kernel.org
This commit is contained in:
Ard Biesheuvel 2023-08-07 18:27:01 +02:00 committed by Borislav Petkov (AMD)
parent d2d7a54f69
commit df9215f152
5 changed files with 31 additions and 36 deletions
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2
Documentation/arch/x86/boot.rst
View File

@ -1417,7 +1417,7 @@ execution context provided by the EFI firmware.
The function prototype for the handover entry point looks like this::
efi_main(void *handle, efi_system_table_t *table, struct boot_params *bp)
efi_stub_entry(void *handle, efi_system_table_t *table, struct boot_params *bp)
'handle' is the EFI image handle passed to the boot loader by the EFI
firmware, 'table' is the EFI system table - these are the first two

22
arch/x86/boot/compressed/efi_mixed.S
View File

@ -26,8 +26,8 @@
* 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
* enter the kernel, it will either branch to the common 64-bit EFI stub
* entrypoint efi_stub_entry() directly, or via 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.
@ -37,21 +37,23 @@
* | efi32_pe_entry |---->| | | +-----------+--+
* +------------------+ | | +------+----------------+ |
* | startup_32 |---->| startup_64_mixed_mode | |
* +------------------+ | | +------+----------------+ V
* | efi32_stub_entry |---->| | | +------------------+
* +------------------+ +------------+ +---->| efi64_stub_entry |
* +-------------+----+
* +------------+ +----------+ |
* | startup_64 |<----| efi_main |<--------------+
* +------------+ +----------+
* +------------------+ | | +------+----------------+ |
* | efi32_stub_entry |---->| | | |
* +------------------+ +------------+ | |
* V |
* +------------+ +----------------+ |
* | startup_64 |<----| efi_stub_entry |<--------+
* +------------+ +----------------+
*/
SYM_FUNC_START(startup_64_mixed_mode)
lea efi32_boot_args(%rip), %rdx
mov 0(%rdx), %edi
mov 4(%rdx), %esi
#ifdef CONFIG_EFI_HANDOVER_PROTOCOL
mov 8(%rdx), %edx // saved bootparams pointer
test %edx, %edx
jnz efi64_stub_entry
jnz efi_stub_entry
#endif
/*
* efi_pe_entry uses MS calling convention, which requires 32 bytes of
* shadow space on the stack even if all arguments are passed in

11
arch/x86/boot/compressed/head_32.S
View File

@ -150,17 +150,6 @@ SYM_FUNC_START(startup_32)
jmp *%eax
SYM_FUNC_END(startup_32)
#ifdef CONFIG_EFI_STUB
SYM_FUNC_START(efi32_stub_entry)
add $0x4, %esp
movl 8(%esp), %esi /* save boot_params pointer */
call efi_main
/* efi_main returns the possibly relocated address of startup_32 */
jmp *%eax
SYM_FUNC_END(efi32_stub_entry)
SYM_FUNC_ALIAS(efi_stub_entry, efi32_stub_entry)
#endif
.text
SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)

12
arch/x86/boot/compressed/head_64.S
View File

@ -542,19 +542,11 @@ trampoline_return:
jmp *%rax
SYM_CODE_END(startup_64)
#ifdef CONFIG_EFI_STUB
#ifdef CONFIG_EFI_HANDOVER_PROTOCOL
#if IS_ENABLED(CONFIG_EFI_MIXED) && IS_ENABLED(CONFIG_EFI_HANDOVER_PROTOCOL)
.org 0x390
#endif
SYM_FUNC_START(efi64_stub_entry)
and $~0xf, %rsp /* realign the stack */
movq %rdx, %rbx /* save boot_params pointer */
call efi_main
movq %rbx,%rsi
leaq rva(startup_64)(%rax), %rax
jmp *%rax
jmp efi_stub_entry
SYM_FUNC_END(efi64_stub_entry)
SYM_FUNC_ALIAS(efi_stub_entry, efi64_stub_entry)
#endif
.text

20
drivers/firmware/efi/libstub/x86-stub.c
View File

@ -817,9 +817,9 @@ static void __noreturn enter_kernel(unsigned long kernel_addr,
* return. On failure, it will exit to the firmware via efi_exit() instead of
* returning.
*/
asmlinkage unsigned long efi_main(efi_handle_t handle,
efi_system_table_t *sys_table_arg,
struct boot_params *boot_params)
void __noreturn efi_stub_entry(efi_handle_t handle,
efi_system_table_t *sys_table_arg,
struct boot_params *boot_params)
{
unsigned long bzimage_addr = (unsigned long)startup_32;
unsigned long buffer_start, buffer_end;
@ -964,7 +964,19 @@ asmlinkage unsigned long efi_main(efi_handle_t handle,
enter_kernel(bzimage_addr, boot_params);
fail:
efi_err("efi_main() failed!\n");
efi_err("efi_stub_entry() failed!\n");
efi_exit(handle, status);
}
#ifdef CONFIG_EFI_HANDOVER_PROTOCOL
#ifndef CONFIG_EFI_MIXED
extern __alias(efi_stub_entry)
void efi32_stub_entry(efi_handle_t handle, efi_system_table_t *sys_table_arg,
struct boot_params *boot_params);
extern __alias(efi_stub_entry)
void efi64_stub_entry(efi_handle_t handle, efi_system_table_t *sys_table_arg,
struct boot_params *boot_params);
#endif
#endif