x86/efistub: Simplify and clean up handover entry code

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

diff --git a/Documentation/arch/x86/boot.rst b/Documentation/arch/x86/boot.rst
index 33520ec..cdbca15 100644 (file)
--- a/Documentation/arch/x86/boot.rst
+++ b/Documentation/arch/x86/boot.rst
@@ -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

diff --git a/arch/x86/boot/compressed/efi_mixed.S b/arch/x86/boot/compressed/efi_mixed.S
index 4ca70bf..dcc562c 100644 (file)
--- a/arch/x86/boot/compressed/efi_mixed.S
+++ b/arch/x86/boot/compressed/efi_mixed.S
@@ -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

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 987ae72..8876ffe 100644 (file)
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -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)
 

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index f732426..e688020 100644 (file)
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -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

diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index 40a10db..3f3b3ed 100644 (file)
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -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