[U-Boot] [RFC 1/1] efi_loader: in situ relocation

Heinrich Schuchardt xypron.glpk at gmx.de
Wed Feb 20 18:12:53 UTC 2019 

On 2/18/19 1:52 AM, AKASHI Takahiro wrote:
> Heinrich,
> 
> On Sat, Feb 16, 2019 at 08:50:43PM +0100, Heinrich Schuchardt wrote:
>> All code and data sections of PE images are already in the correct relative
>> location when loaded into memory. There is not need to copy them once
>> again.
> 
> While I'm not very familiar with how PE image is created (in EDK2),
The relevant reference is the Microsoft Portable Executable and
Common Object File Format Specification. The latest version as PDF that
I found is revision 11, Jan 23rd, 2017. The citations are from that
version. Later versions are available as HTML.

> what I understand in Alex's code is
> * All the code and data are located starting 0x0 (in virtual space)
The header provides a field ImageBase. If you load the image at this
address there is no need for relocation. I could not find any rule
saying ImageBase has to be zero. It has be a multiple of 64 KiB. For
Windows non-zero defaults are provided in the spec.

> * Sections in PE image may not be sorted in ascending order
The spec says: "The physical offset for section data is the same as the
RVA". The relative virtual address is defined as "In an image file, the
address of an item after it is loaded into memory, with the base address
of the image file subtracted from it."

> * There may be some gaps (more than one page) between sections,
>   probably, due to alignment requirements or BSS
Yes, due to alignment there may be some gap filling bytes.

> 
> Do you say that those assumptions are no longer correct?
The most important sentence concerning relocations in the spec is:

"If the image is loaded at its preferred base, ... the base relocations
do not have to be applied."

This implies that there is not need to modify the relative position of
sections after loading.

Best regards

Heinrich

> 
> Thanks,
> -Takahiro Akashi
> 
>> Signed-off-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
>> ---
>>  lib/efi_loader/efi_image_loader.c | 64 ++++++-------------------------
>>  1 file changed, 11 insertions(+), 53 deletions(-)
>>
>> diff --git a/lib/efi_loader/efi_image_loader.c b/lib/efi_loader/efi_image_loader.c
>> index fe66e7b9ffe..6146acc6b6f 100644
>> --- a/lib/efi_loader/efi_image_loader.c
>> +++ b/lib/efi_loader/efi_image_loader.c
>> @@ -2,7 +2,7 @@
>>  /*
>>   *  EFI image loader
>>   *
>> - *  based partly on wine code
>> + *  based partly on Wine code
>>   *
>>   *  Copyright (c) 2016 Alexander Graf
>>   */
>> @@ -219,16 +219,12 @@ efi_status_t efi_load_pe(struct efi_loaded_image_obj *handle, void *efi,
>>  {
>>  	IMAGE_NT_HEADERS32 *nt;
>>  	IMAGE_DOS_HEADER *dos;
>> -	IMAGE_SECTION_HEADER *sections;
>> -	int num_sections;
>> -	void *efi_reloc;
>>  	int i;
>>  	const IMAGE_BASE_RELOCATION *rel;
>>  	unsigned long rel_size;
>>  	int rel_idx = IMAGE_DIRECTORY_ENTRY_BASERELOC;
>>  	uint64_t image_base;
>>  	uint64_t image_size;
>> -	unsigned long virt_size = 0;
>>  	int supported = 0;
>>  
>>  	dos = efi;
>> @@ -255,85 +251,47 @@ efi_status_t efi_load_pe(struct efi_loaded_image_obj *handle, void *efi,
>>  		return EFI_LOAD_ERROR;
>>  	}
>>  
>> -	/* Calculate upper virtual address boundary */
>> -	num_sections = nt->FileHeader.NumberOfSections;
>> -	sections = (void *)&nt->OptionalHeader +
>> -			    nt->FileHeader.SizeOfOptionalHeader;
>> -
>> -	for (i = num_sections - 1; i >= 0; i--) {
>> -		IMAGE_SECTION_HEADER *sec = &sections[i];
>> -		virt_size = max_t(unsigned long, virt_size,
>> -				  sec->VirtualAddress + sec->Misc.VirtualSize);
>> -	}
>> -
>>  	/* Read 32/64bit specific header bits */
>>  	if (nt->OptionalHeader.Magic == IMAGE_NT_OPTIONAL_HDR64_MAGIC) {
>>  		IMAGE_NT_HEADERS64 *nt64 = (void *)nt;
>>  		IMAGE_OPTIONAL_HEADER64 *opt = &nt64->OptionalHeader;
>> +
>>  		image_base = opt->ImageBase;
>>  		image_size = opt->SizeOfImage;
>>  		efi_set_code_and_data_type(loaded_image_info, opt->Subsystem);
>> -		efi_reloc = efi_alloc(virt_size,
>> -				      loaded_image_info->image_code_type);
>> -		if (!efi_reloc) {
>> -			printf("%s: Could not allocate %lu bytes\n",
>> -			       __func__, virt_size);
>> -			return EFI_OUT_OF_RESOURCES;
>> -		}
>> -		handle->entry = efi_reloc + opt->AddressOfEntryPoint;
>> +		handle->entry = efi + opt->AddressOfEntryPoint;
>>  		rel_size = opt->DataDirectory[rel_idx].Size;
>> -		rel = efi_reloc + opt->DataDirectory[rel_idx].VirtualAddress;
>> -		virt_size = ALIGN(virt_size, opt->SectionAlignment);
>> +		rel = efi + opt->DataDirectory[rel_idx].VirtualAddress;
>>  	} else if (nt->OptionalHeader.Magic == IMAGE_NT_OPTIONAL_HDR32_MAGIC) {
>>  		IMAGE_OPTIONAL_HEADER32 *opt = &nt->OptionalHeader;
>> +
>>  		image_base = opt->ImageBase;
>>  		image_size = opt->SizeOfImage;
>>  		efi_set_code_and_data_type(loaded_image_info, opt->Subsystem);
>> -		efi_reloc = efi_alloc(virt_size,
>> -				      loaded_image_info->image_code_type);
>> -		if (!efi_reloc) {
>> -			printf("%s: Could not allocate %lu bytes\n",
>> -			       __func__, virt_size);
>> -			return EFI_OUT_OF_RESOURCES;
>> -		}
>> -		handle->entry = efi_reloc + opt->AddressOfEntryPoint;
>> +		handle->entry = efi + opt->AddressOfEntryPoint;
>>  		rel_size = opt->DataDirectory[rel_idx].Size;
>> -		rel = efi_reloc + opt->DataDirectory[rel_idx].VirtualAddress;
>> -		virt_size = ALIGN(virt_size, opt->SectionAlignment);
>> +		rel = efi + opt->DataDirectory[rel_idx].VirtualAddress;
>>  	} else {
>>  		printf("%s: Invalid optional header magic %x\n", __func__,
>>  		       nt->OptionalHeader.Magic);
>>  		return EFI_LOAD_ERROR;
>>  	}
>>  
>> -	/* Load sections into RAM */
>> -	for (i = num_sections - 1; i >= 0; i--) {
>> -		IMAGE_SECTION_HEADER *sec = &sections[i];
>> -		memset(efi_reloc + sec->VirtualAddress, 0,
>> -		       sec->Misc.VirtualSize);
>> -		memcpy(efi_reloc + sec->VirtualAddress,
>> -		       efi + sec->PointerToRawData,
>> -		       sec->SizeOfRawData);
>> -	}
>> -
>>  	/* Run through relocations */
>> -	if (efi_loader_relocate(rel, rel_size, efi_reloc,
>> +	if (efi_loader_relocate(rel, rel_size, efi,
>>  				(unsigned long)image_base) != EFI_SUCCESS) {
>> -		efi_free_pages((uintptr_t) efi_reloc,
>> -			       (virt_size + EFI_PAGE_MASK) >> EFI_PAGE_SHIFT);
>>  		return EFI_LOAD_ERROR;
>>  	}
>>  
>>  	/* Flush cache */
>> -	flush_cache((ulong)efi_reloc,
>> -		    ALIGN(virt_size, EFI_CACHELINE_SIZE));
>> +	flush_cache((ulong)efi, ALIGN(image_size, EFI_CACHELINE_SIZE));
>>  	invalidate_icache_all();
>>  
>>  	/* Populate the loaded image interface bits */
>>  	loaded_image_info->image_base = efi;
>>  	loaded_image_info->image_size = image_size;
>> -	handle->reloc_base = efi_reloc;
>> -	handle->reloc_size = virt_size;
>> +	handle->reloc_base = efi;
>> +	handle->reloc_size = image_size;
>>  
>>  	return EFI_SUCCESS;
>>  }
>> -- 
>> 2.20.1
>>
>

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