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x86/efistub: Simplify and clean up handover entry code

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From: Ard Biesheuvel <ardb@kernel.org>

[ Commit df9215f152 upstream ]

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
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ard Biesheuvel
2024-03-04 12:19:41 +01:00
committed by Greg Kroah-Hartman
parent 33d064aecd
commit f0acafd6f7
5 changed files with 31 additions and 36 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
Documentation/x86/boot.rst
View File

@@ -1416,7 +1416,7 @@ execution context provided by the EFI firmware.
The function prototype for the handover entry point looks like this:: 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 '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 firmware, 'table' is the EFI system table - these are the first two

22
arch/x86/boot/compressed/efi_mixed.S
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@@ -26,8 +26,8 @@
* When booting in 64-bit mode on 32-bit EFI firmware, startup_64_mixed_mode() * 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 * 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 * 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 * enter the kernel, it will either branch to the common 64-bit EFI stub
* entrypoint at offset 0x390 in the image, or to the 64-bit EFI PE/COFF * 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 * 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 * struct bootparams pointer as the third argument, so the presence of such a
* pointer is used to disambiguate. * pointer is used to disambiguate.
@@ -37,21 +37,23 @@
* | efi32_pe_entry |---->| | | +-----------+--+ * | efi32_pe_entry |---->| | | +-----------+--+
* +------------------+ | | +------+----------------+ | * +------------------+ | | +------+----------------+ |
* | startup_32 |---->| startup_64_mixed_mode | | * | startup_32 |---->| startup_64_mixed_mode | |
* +------------------+ | | +------+----------------+ V * +------------------+ | | +------+----------------+ |
* | efi32_stub_entry |---->| | | +------------------+ * | efi32_stub_entry |---->| | | |
* +------------------+ +------------+ +---->| efi64_stub_entry | * +------------------+ +------------+ | |
* +-------------+----+ * V |
* +------------+ +----------+ | * +------------+ +----------------+ |
* | startup_64 |<----| efi_main |<--------------+ * | startup_64 |<----| efi_stub_entry |<--------+
* +------------+ +----------+ * +------------+ +----------------+
*/ */
SYM_FUNC_START(startup_64_mixed_mode) SYM_FUNC_START(startup_64_mixed_mode)
lea efi32_boot_args(%rip), %rdx lea efi32_boot_args(%rip), %rdx
mov 0(%rdx), %edi mov 0(%rdx), %edi
mov 4(%rdx), %esi mov 4(%rdx), %esi
#ifdef CONFIG_EFI_HANDOVER_PROTOCOL
mov 8(%rdx), %edx // saved bootparams pointer mov 8(%rdx), %edx // saved bootparams pointer
test %edx, %edx test %edx, %edx
jnz efi64_stub_entry jnz efi_stub_entry
#endif
/* /*
* efi_pe_entry uses MS calling convention, which requires 32 bytes of * efi_pe_entry uses MS calling convention, which requires 32 bytes of
* shadow space on the stack even if all arguments are passed in * shadow space on the stack even if all arguments are passed in

11
arch/x86/boot/compressed/head_32.S
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@@ -150,17 +150,6 @@ SYM_FUNC_START(startup_32)
jmp *%eax jmp *%eax
SYM_FUNC_END(startup_32) 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 .text
SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)

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

@@ -474,19 +474,11 @@ SYM_CODE_START(startup_64)
jmp *%rax jmp *%rax
SYM_CODE_END(startup_64) SYM_CODE_END(startup_64)
#ifdef CONFIG_EFI_STUB #if IS_ENABLED(CONFIG_EFI_MIXED) && IS_ENABLED(CONFIG_EFI_HANDOVER_PROTOCOL)
#ifdef CONFIG_EFI_HANDOVER_PROTOCOL
.org 0x390 .org 0x390
#endif
SYM_FUNC_START(efi64_stub_entry) SYM_FUNC_START(efi64_stub_entry)
and $~0xf, %rsp /* realign the stack */ jmp efi_stub_entry
movq %rdx, %rbx /* save boot_params pointer */
call efi_main
movq %rbx,%rsi
leaq rva(startup_64)(%rax), %rax
jmp *%rax
SYM_FUNC_END(efi64_stub_entry) SYM_FUNC_END(efi64_stub_entry)
SYM_FUNC_ALIAS(efi_stub_entry, efi64_stub_entry)
#endif #endif
.text .text

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

@@ -774,9 +774,9 @@ static void __noreturn enter_kernel(unsigned long kernel_addr,
* return. On failure, it will exit to the firmware via efi_exit() instead of * return. On failure, it will exit to the firmware via efi_exit() instead of
* returning. * returning.
*/ */
asmlinkage unsigned long efi_main(efi_handle_t handle, void __noreturn efi_stub_entry(efi_handle_t handle,
efi_system_table_t *sys_table_arg, efi_system_table_t *sys_table_arg,
struct boot_params *boot_params) struct boot_params *boot_params)
{ {
unsigned long bzimage_addr = (unsigned long)startup_32; unsigned long bzimage_addr = (unsigned long)startup_32;
unsigned long buffer_start, buffer_end; unsigned long buffer_start, buffer_end;
@@ -919,7 +919,19 @@ asmlinkage unsigned long efi_main(efi_handle_t handle,
enter_kernel(bzimage_addr, boot_params); enter_kernel(bzimage_addr, boot_params);
fail: fail:
efi_err("efi_main() failed!\n"); efi_err("efi_stub_entry() failed!\n");
efi_exit(handle, status); 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