[U-Boot] [PATCH 1/1] x86: detect unsupported relocation types

[Heinrich Schuchardt]

On 10/23/2018 11:13 AM, Hannes Schmelzer wrote:
> 
> On 10/13/18 3:30 AM, Heinrich Schuchardt wrote:
>> Currently we support only relocations of type ELF64_R_TYPE or
>> ELF32_R_TYPE.
>> We should be warned if other relocation types appear in the relocation
>> sections.
>>
>> This type of message has helped to identify code overwriting a relocation
>> section before relocation and incorrect parsing of relocation tables.
>>
>> Signed-off-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
>> ---
>>   arch/x86/lib/relocate.c | 18 ++++++++++++++++++
>>   1 file changed, 18 insertions(+)
>>
>> diff --git a/arch/x86/lib/relocate.c b/arch/x86/lib/relocate.c
>> index ed10755d9c..01e619d20b 100644
>> --- a/arch/x86/lib/relocate.c
>> +++ b/arch/x86/lib/relocate.c
>> @@ -53,6 +53,15 @@ static void do_elf_reloc_fixups64(unsigned int
>> text_base, uintptr_t size,
>>       Elf64_Addr *offset_ptr_ram;
>>         do {
>> +        unsigned long long type = ELF64_R_TYPE(re_src->r_info);
>> +
>> +        if (type != R_X86_64_RELATIVE) {
>> +            printf("%s: unsupported relocation type 0x%llx "
>> +                   "at %p, ",__func__, type, re_src);
>> +            printf("offset = 0x%llx\n", re_src->r_offset);
>> +            continue;
>> +        }
>> +
>>           /* Get the location from the relocation entry */
>>           offset_ptr_rom = (Elf64_Addr *)(uintptr_t)re_src->r_offset;
>>   @@ -91,6 +100,15 @@ static void do_elf_reloc_fixups32(unsigned int
>> text_base, uintptr_t size,
>>       Elf32_Addr *offset_ptr_ram;
>>         do {
>> +        unsigned int type = ELF32_R_TYPE(re_src->r_info);
>> +
>> +        if (type != R_386_RELATIVE) {
>> +            printf("%s: unsupported relocation type 0x%x "
>> +                   "at %p, ",__func__, type, re_src);
>> +            printf("offset = 0x%x\n", re_src->r_offset);
>> +            continue;
>> +        }
>> +
>>           /* Get the location from the relocation entry */
>>           offset_ptr_rom = (Elf32_Addr *)(uintptr_t)re_src->r_offset;
>>   
> Hi Heinrich,
> i just merged recent u-boot master into my devbranch and ran it on my
> board:
> 
> -- 
> U-Boot 2018.11-rc2-00728-g85a448b (Oct 23 2018 - 10:50:53 +0200)
> 
> CPU: x86, vendor AMD, device 5a2h
> DRAM:  119.6 MiB
> do_elf_reloc_fixups32: unsupported relocation type 0x1 at 0204d3d0,
> offset = 0x2000087
> do_elf_reloc_fixups32: unsupported relocation type 0x2 at 0204d3d8,
> offset = 0x2000091
> Bus 0: OK
> ---
> 
> now i get such relocation warnings, can you help me in this how to deal
> with that?
> 
> I'm starting u-boot as a payload from coreboot.
> 
> thanks!
> 
> cheers,
> Hannes
> 
> 

Hello Hannes,

thanks for reporting the problem.

There are two possible reasons:

a) The build process introduces relocations of the reported type.
b) The relocation records are overwritten before relocation. This
happens if you update uninitialized globals.

To analyze your problem further, please, provide instructions for
building your version of U-Boot (repository, commit, config). That will
allow to check for a).

Coreboot can be run on QEMU (https://www.coreboot.org/QEMU). QEMU would
allow to analyze case b). Are you able to reproduce the problem with QEMU?

Best regards

Heinrich