efi/x86: Avoid using code32_start

code32_start is meant for 16-bit real-mode bootloaders to inform the
kernel where the 32-bit protected mode code starts. Nothing in the
protected mode kernel except the EFI stub uses it.

efi_main() currently returns boot_params, with code32_start set inside it
to tell efi_stub_entry() where startup_32 is located. Since it was invoked
by efi_stub_entry() in the first place, boot_params is already known.
Return the address of startup_32 instead.

This will allow a 64-bit kernel to live above 4Gb, for example, and it's
cleaner as well.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200301230436.2246909-5-nivedita@alum.mit.edu
Link: https://lore.kernel.org/r/20200308080859.21568-13-ardb@kernel.org

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 2f8138b..e013bdc 100644 (file)
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -156,9 +156,8 @@ SYM_FUNC_END(startup_32)
 SYM_FUNC_START(efi32_stub_entry)
 SYM_FUNC_START_ALIAS(efi_stub_entry)
        add     $0x4, %esp
+       movl    8(%esp), %esi   /* save boot_params pointer */
        call    efi_main
-       movl    %eax, %esi
-       movl    BP_code32_start(%esi), %eax
        leal    startup_32(%eax), %eax
        jmp     *%eax
 SYM_FUNC_END(efi32_stub_entry)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index fabbd4c..6a4ff91 100644 (file)
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -472,9 +472,9 @@ SYM_CODE_END(startup_64)
 SYM_FUNC_START(efi64_stub_entry)
 SYM_FUNC_START_ALIAS(efi_stub_entry)
        and     $~0xf, %rsp                     /* realign the stack */
+       movq    %rdx, %rbx                      /* save boot_params pointer */
        call    efi_main
-       movq    %rax,%rsi
-       movl    BP_code32_start(%esi), %eax
+       movq    %rbx,%rsi
        leaq    startup_64(%rax), %rax
        jmp     *%rax
 SYM_FUNC_END(efi64_stub_entry)

diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index 5c7ee3d..3ca07ad 100644 (file)
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -88,7 +88,6 @@ static void __used common(void)
        OFFSET(BP_kernel_alignment, boot_params, hdr.kernel_alignment);
        OFFSET(BP_init_size, boot_params, hdr.init_size);
        OFFSET(BP_pref_address, boot_params, hdr.pref_address);
-       OFFSET(BP_code32_start, boot_params, hdr.code32_start);
 
        BLANK();
        DEFINE(PTREGS_SIZE, sizeof(struct pt_regs));

diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index 9db9883..7f3e97c 100644 (file)
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -703,10 +703,11 @@ static efi_status_t exit_boot(struct boot_params *boot_params, void *handle)
 }
 
 /*
- * On success we return a pointer to a boot_params structure, and NULL
- * on failure.
+ * On success, we return the address of startup_32, which has potentially been
+ * relocated by efi_relocate_kernel.
+ * On failure, we exit to the firmware via efi_exit instead of returning.
  */
-struct boot_params *efi_main(efi_handle_t handle,
+unsigned long efi_main(efi_handle_t handle,
                             efi_system_table_t *sys_table_arg,
                             struct boot_params *boot_params)
 {
@@ -736,7 +737,6 @@ struct boot_params *efi_main(efi_handle_t handle,
                        goto fail;
                }
        }
-       hdr->code32_start = (u32)bzimage_addr;
 
        /*
         * efi_pe_entry() may have been called before efi_main(), in which
@@ -799,7 +799,7 @@ struct boot_params *efi_main(efi_handle_t handle,
                goto fail;
        }
 
-       return boot_params;
+       return bzimage_addr;
 fail:
        efi_printk("efi_main() failed!\n");