[PATCH v3 8/8] arm64: efi: split Image code and data into separate PE/COFF sections

[Mark Rutland]

On Thu, Mar 23, 2017 at 07:00:51PM +0000, Ard Biesheuvel wrote:
> 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 and .init.text, and a .data section with
> read-write permissions, covering .init.data, .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 at linaro.org>

Acked-by: Mark Rutland <mark.rutland at arm.com>

Mark.

> ---
>  arch/arm64/kernel/efi-header.S  | 23 +++++++++++++++-----
>  arch/arm64/kernel/vmlinux.lds.S |  2 ++
>  2 files changed, 20 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/kernel/efi-header.S b/arch/arm64/kernel/efi-header.S
> index 7637226ea9ca..613fc3000677 100644
> --- a/arch/arm64/kernel/efi-header.S
> +++ b/arch/arm64/kernel/efi-header.S
> @@ -27,8 +27,8 @@ optional_header:
>  	.short	PE_OPT_MAGIC_PE32PLUS			// PE32+ format
>  	.byte	0x02					// MajorLinkerVersion
>  	.byte	0x14					// MinorLinkerVersion
> -	.long	_end - efi_header_end			// SizeOfCode
> -	.long	0					// SizeOfInitializedData
> +	.long	__initdata_begin - efi_header_end	// SizeOfCode
> +	.long	__pecoff_data_size			// SizeOfInitializedData
>  	.long	0					// SizeOfUninitializedData
>  	.long	__efistub_entry - _head			// AddressOfEntryPoint
>  	.long	efi_header_end - _head			// BaseOfCode
> @@ -74,9 +74,9 @@ extra_header_fields:
>  	// Section table
>  section_table:
>  	.ascii	".text\0\0\0"
> -	.long	_end - efi_header_end			// VirtualSize
> +	.long	__initdata_begin - efi_header_end	// VirtualSize
>  	.long	efi_header_end - _head			// VirtualAddress
> -	.long	_edata - efi_header_end			// SizeOfRawData
> +	.long	__initdata_begin - efi_header_end	// SizeOfRawData
>  	.long	efi_header_end - _head			// PointerToRawData
>  
>  	.long	0					// PointerToRelocations
> @@ -84,7 +84,20 @@ section_table:
>  	.short	0					// NumberOfRelocations
>  	.short	0					// NumberOfLineNumbers
>  	.long	IMAGE_SCN_CNT_CODE | \
> -		IMAGE_SCN_MEM_EXECUTE | \
> +		IMAGE_SCN_MEM_READ | \
> +		IMAGE_SCN_MEM_EXECUTE			// Characteristics
> +
> +	.ascii	".data\0\0\0"
> +	.long	__pecoff_data_size			// VirtualSize
> +	.long	__initdata_begin - _head		// VirtualAddress
> +	.long	__pecoff_data_rawsize			// SizeOfRawData
> +	.long	__initdata_begin - _head		// 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
>  
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index 2c93d259046c..987a00ee446c 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -213,6 +213,7 @@ SECTIONS
>  	}
>  
>  	PECOFF_EDATA_PADDING
> +	__pecoff_data_rawsize = ABSOLUTE(. - __initdata_begin);
>  	_edata = .;
>  
>  	BSS_SECTION(0, 0, 0)
> @@ -228,6 +229,7 @@ SECTIONS
>  	. += RESERVED_TTBR0_SIZE;
>  #endif
>  
> +	__pecoff_data_size = ABSOLUTE(. - __initdata_begin);
>  	_end = .;
>  
>  	STABS_DEBUG
> -- 
> 2.9.3
>