arm64: head: tidy up the Image header definition

Even though support for EFI boot remains entirely optional for arm64,
it is unlikely that we will ever be able to repurpose the image header
fields that the EFI loader relies on, i.e., the magic NOP at offset
0x0 and the PE header address at offset 0x3c.

So let's factor out the differences into a 'efi_signature_nop' macro and
a local symbol representing the PE header address, and move the
conditional definitions into efi-header.S, taking into account whether
CONFIG_EFI is enabled or not. While at it, switch to a signature NOP
that behaves more like a NOP, i.e., one that only clobbers the
flags.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20201117124729.12642-4-ardb@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/kernel/efi-header.S b/arch/arm64/kernel/efi-header.S
index ddaf57d825b5c759159cd23122bcdfdae5157082..28d8a5dca5f129784b158589a3c4c1d231ffd6e9 100644 (file)
--- a/arch/arm64/kernel/efi-header.S
+++ b/arch/arm64/kernel/efi-header.S
@@ -7,7 +7,27 @@
 #include <linux/pe.h>
 #include <linux/sizes.h>
 
+       .macro  efi_signature_nop
+#ifdef CONFIG_EFI
+.L_head:
+       /*
+        * This ccmp instruction has no meaningful effect except that
+        * its opcode forms the magic "MZ" signature required by UEFI.
+        */
+       ccmp    x18, #0, #0xd, pl
+#else
+       /*
+        * Bootloaders may inspect the opcode at the start of the kernel
+        * image to decide if the kernel is capable of booting via UEFI.
+        * So put an ordinary NOP here, not the "MZ.." pseudo-nop above.
+        */
+       nop
+#endif
+       .endm
+
        .macro  __EFI_PE_HEADER
+#ifdef CONFIG_EFI
+       .set    .Lpe_header_offset, . - .L_head
        .long   PE_MAGIC
        .short  IMAGE_FILE_MACHINE_ARM64                // Machine
        .short  .Lsection_count                         // NumberOfSections
@@ -26,8 +46,8 @@
        .long   __initdata_begin - .Lefi_header_end     // SizeOfCode
        .long   __pecoff_data_size                      // SizeOfInitializedData
        .long   0                                       // SizeOfUninitializedData
-       .long   __efistub_efi_pe_entry - _head          // AddressOfEntryPoint
-       .long   .Lefi_header_end - _head                // BaseOfCode
+       .long   __efistub_efi_pe_entry - .L_head        // AddressOfEntryPoint
+       .long   .Lefi_header_end - .L_head              // BaseOfCode
 
        .quad   0                                       // ImageBase
        .long   SEGMENT_ALIGN                           // SectionAlignment
@@ -40,10 +60,10 @@
        .short  0                                       // MinorSubsystemVersion
        .long   0                                       // Win32VersionValue
 
-       .long   _end - _head                            // SizeOfImage
+       .long   _end - .L_head                          // SizeOfImage
 
        // Everything before the kernel image is considered part of the header
-       .long   .Lefi_header_end - _head                // SizeOfHeaders
+       .long   .Lefi_header_end - .L_head              // SizeOfHeaders
        .long   0                                       // CheckSum
        .short  IMAGE_SUBSYSTEM_EFI_APPLICATION         // Subsystem
        .short  0                                       // DllCharacteristics
@@ -62,7 +82,7 @@
        .quad   0                                       // BaseRelocationTable
 
 #ifdef CONFIG_DEBUG_EFI
-       .long   .Lefi_debug_table - _head               // DebugTable
+       .long   .Lefi_debug_table - .L_head             // DebugTable
        .long   .Lefi_debug_table_size
 #endif
 
@@ -70,9 +90,9 @@
 .Lsection_table:
        .ascii  ".text\0\0\0"
        .long   __initdata_begin - .Lefi_header_end     // VirtualSize
-       .long   .Lefi_header_end - _head                // VirtualAddress
+       .long   .Lefi_header_end - .L_head              // VirtualAddress
        .long   __initdata_begin - .Lefi_header_end     // SizeOfRawData
-       .long   .Lefi_header_end - _head                // PointerToRawData
+       .long   .Lefi_header_end - .L_head              // PointerToRawData
 
        .long   0                                       // PointerToRelocations
        .long   0                                       // PointerToLineNumbers
@@ -84,9 +104,9 @@
 
        .ascii  ".data\0\0\0"
        .long   __pecoff_data_size                      // VirtualSize
-       .long   __initdata_begin - _head                // VirtualAddress
+       .long   __initdata_begin - .L_head              // VirtualAddress
        .long   __pecoff_data_rawsize                   // SizeOfRawData
-       .long   __initdata_begin - _head                // PointerToRawData
+       .long   __initdata_begin - .L_head              // PointerToRawData
 
        .long   0                                       // PointerToRelocations
        .long   0                                       // PointerToLineNumbers
@@ -121,7 +141,7 @@
        .long   IMAGE_DEBUG_TYPE_CODEVIEW               // Type
        .long   .Lefi_debug_entry_size                  // SizeOfData
        .long   0                                       // RVA
-       .long   .Lefi_debug_entry - _head               // FileOffset
+       .long   .Lefi_debug_entry - .L_head             // FileOffset
 
        .set    .Lefi_debug_table_size, . - .Lefi_debug_table
        .previous
@@ -140,4 +160,7 @@
 
        .balign SEGMENT_ALIGN
 .Lefi_header_end:
+#else
+       .set    .Lpe_header_offset, 0x0
+#endif
        .endm

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index d8d9caf02834e03f3b1da6201cc57b2dbf59eabe..c1f8f2c5be47ed29612fe2b8e0d5e3876d83aca4 100644 (file)
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -58,21 +58,11 @@
  * in the entry routines.
  */
        __HEAD
-_head:
        /*
         * DO NOT MODIFY. Image header expected by Linux boot-loaders.
         */
-#ifdef CONFIG_EFI
-       /*
-        * This add instruction has no meaningful effect except that
-        * its opcode forms the magic "MZ" signature required by UEFI.
-        */
-       add     x13, x18, #0x16
-       b       primary_entry
-#else
+       efi_signature_nop                       // special NOP to identity as PE/COFF executable
        b       primary_entry                   // branch to kernel start, magic
-       .long   0                               // reserved
-#endif
        .quad   0                               // Image load offset from start of RAM, little-endian
        le64sym _kernel_size_le                 // Effective size of kernel image, little-endian
        le64sym _kernel_flags_le                // Informative flags, little-endian
@@ -80,14 +70,9 @@ _head:
        .quad   0                               // reserved
        .quad   0                               // reserved
        .ascii  ARM64_IMAGE_MAGIC               // Magic number
-#ifdef CONFIG_EFI
-       .long   pe_header - _head               // Offset to the PE header.
+       .long   .Lpe_header_offset              // Offset to the PE header.
 
-pe_header:
        __EFI_PE_HEADER
-#else
-       .long   0                               // reserved
-#endif
 
        __INIT