arm/efi: Split zImage code and data into separate PE/COFF sections

To prevent unintended modifications to the kernel text (malicious or
otherwise) while running the EFI stub, describe the kernel image as
two separate sections: a .text section with read-execute permissions,
covering .text, .rodata, .piggytext and the GOT sections (which the
stub does not care about anyway), and a .data section with read-write
permissions, covering .data and .bss.

This relies on the firmware to actually take the section permission
flags into account, but this is something that is currently being
implemented in EDK2, which means we will likely start seeing it in
the wild between one and two years from now.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20170818194947.19347-12-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/arm/boot/compressed/efi-header.S b/arch/arm/boot/compressed/efi-header.S
index 542e1ad432aea5aedeba09e303de6dc03ed4f7a1..c94a88ae834dc3b28418279e188fdbfb8ac7da2c 100644 (file)
--- a/arch/arm/boot/compressed/efi-header.S
+++ b/arch/arm/boot/compressed/efi-header.S
@@ -54,20 +54,22 @@ coff_header:
                        IMAGE_FILE_EXECUTABLE_IMAGE | \
                        IMAGE_FILE_LINE_NUMS_STRIPPED   @ Characteristics
 
+#define __pecoff_code_size (__pecoff_data_start - __efi_start)
+
 optional_header:
                .short  PE_OPT_MAGIC_PE32               @ PE32 format
                .byte   0x02                            @ MajorLinkerVersion
                .byte   0x14                            @ MinorLinkerVersion
-               .long   _end - __efi_start              @ SizeOfCode
-               .long   0                               @ SizeOfInitializedData
+               .long   __pecoff_code_size              @ SizeOfCode
+               .long   __pecoff_data_size              @ SizeOfInitializedData
                .long   0                               @ SizeOfUninitializedData
                .long   efi_stub_entry - start          @ AddressOfEntryPoint
                .long   start_offset                    @ BaseOfCode
-               .long   0                               @ BaseOfData
+               .long   __pecoff_data_start - start     @ BaseOfData
 
 extra_header_fields:
                .long   0                               @ ImageBase
-               .long   SZ_512                          @ SectionAlignment
+               .long   SZ_4K                           @ SectionAlignment
                .long   SZ_512                          @ FileAlignment
                .short  0                               @ MajorOsVersion
                .short  0                               @ MinorOsVersion
@@ -77,7 +79,7 @@ extra_header_fields:
                .short  0                               @ MinorSubsystemVersion
                .long   0                               @ Win32VersionValue
 
-               .long   _end - start                    @ SizeOfImage
+               .long   __pecoff_end - start            @ SizeOfImage
                .long   start_offset                    @ SizeOfHeaders
                .long   0                               @ CheckSum
                .short  IMAGE_SUBSYSTEM_EFI_APPLICATION @ Subsystem
@@ -98,9 +100,9 @@ extra_header_fields:
 
 section_table:
                .ascii  ".text\0\0\0"
-               .long   _end - __efi_start              @ VirtualSize
+               .long   __pecoff_code_size              @ VirtualSize
                .long   __efi_start                     @ VirtualAddress
-               .long   _edata - __efi_start            @ SizeOfRawData
+               .long   __pecoff_code_size              @ SizeOfRawData
                .long   __efi_start                     @ PointerToRawData
                .long   0                               @ PointerToRelocations
                .long   0                               @ PointerToLineNumbers
@@ -108,12 +110,24 @@ section_table:
                .short  0                               @ NumberOfLineNumbers
                .long   IMAGE_SCN_CNT_CODE | \
                        IMAGE_SCN_MEM_READ | \
-                       IMAGE_SCN_MEM_WRITE | \
                        IMAGE_SCN_MEM_EXECUTE           @ Characteristics
 
+               .ascii  ".data\0\0\0"
+               .long   __pecoff_data_size              @ VirtualSize
+               .long   __pecoff_data_start - start     @ VirtualAddress
+               .long   __pecoff_data_rawsize           @ SizeOfRawData
+               .long   __pecoff_data_start - start     @ PointerToRawData
+               .long   0                               @ PointerToRelocations
+               .long   0                               @ PointerToLineNumbers
+               .short  0                               @ NumberOfRelocations
+               .short  0                               @ NumberOfLineNumbers
+               .long   IMAGE_SCN_CNT_INITIALIZED_DATA | \
+                       IMAGE_SCN_MEM_READ | \
+                       IMAGE_SCN_MEM_WRITE             @ Characteristics
+
                .set    section_count, (. - section_table) / 40
 
-               .align  9
+               .align  12
 __efi_start:
 #endif
                .endm

diff --git a/arch/arm/boot/compressed/vmlinux.lds.S b/arch/arm/boot/compressed/vmlinux.lds.S
index 81c493156ce87e12a4719268076c861da18e7a53..7a4c59154361d00ee88c2d03cb6af5aa8cace7e7 100644 (file)
--- a/arch/arm/boot/compressed/vmlinux.lds.S
+++ b/arch/arm/boot/compressed/vmlinux.lds.S
@@ -48,13 +48,6 @@ SECTIONS
     *(.rodata)
     *(.rodata.*)
   }
-  .data : {
-    /*
-     * The EFI stub always executes from RAM, and runs strictly before the
-     * decompressor, so we can make an exception for its r/w data, and keep it
-     */
-    *(.data.efistub)
-  }
   .piggydata : {
     *(.piggydata)
   }
@@ -70,6 +63,26 @@ SECTIONS
   /* ensure the zImage file size is always a multiple of 64 bits */
   /* (without a dummy byte, ld just ignores the empty section) */
   .pad                 : { BYTE(0); . = ALIGN(8); }
+
+#ifdef CONFIG_EFI_STUB
+  .data : ALIGN(4096) {
+    __pecoff_data_start = .;
+    /*
+     * The EFI stub always executes from RAM, and runs strictly before the
+     * decompressor, so we can make an exception for its r/w data, and keep it
+     */
+    *(.data.efistub)
+    __pecoff_data_end = .;
+
+    /*
+     * PE/COFF mandates a file size which is a multiple of 512 bytes if the
+     * section size equals or exceeds 4 KB
+     */
+    . = ALIGN(512);
+  }
+  __pecoff_data_rawsize = . - ADDR(.data);
+#endif
+
   _edata = .;
 
   _magic_sig = ZIMAGE_MAGIC(0x016f2818);
@@ -84,6 +97,9 @@ SECTIONS
   . = ALIGN(8);                /* the stack must be 64-bit aligned */
   .stack               : { *(.stack) }
 
+  PROVIDE(__pecoff_data_size = ALIGN(512) - ADDR(.data));
+  PROVIDE(__pecoff_end = ALIGN(512));
+
   .stab 0              : { *(.stab) }
   .stabstr 0           : { *(.stabstr) }
   .stab.excl 0         : { *(.stab.excl) }