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bpf: fix false overflow in eBPF ELF backend linker

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When performing DISP{16,32} relocations, the eBPF ELF backend linker
needs to convert the relocation from an address into a signed number
of 64-bit words (minus one) to jump.

Because of this unsigned-to-signed conversion, special care needs to
be taken when dividing to ensure the sign bits remain correct.
Otherwise, a false relocation overflow error can be triggered.

bfd/ChangeLog

2020-08-07  David Faust  <david.faust@oracle.com>

	* elf64-bpf.c (bpf_elf_relocate_section): Ensure signed division for
	DISP16 and DISP32 relocations.

ld/ChangeLog

2020-08-07  David Faust  <david.faust@oracle.com>

	* testsuite/ld-bpf/call-3.s: New file.
	* testsuite/ld-bpf/call-3.d: Likewise.
This commit is contained in:
David Faust 2020-08-07 20:36:47 +02:00 • committed by Jose E. Marchesi
parent fe4c3d430b
commit d844f10ac2
3 changed files with 15 additions and 4 deletions
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5
bfd/ChangeLog
View file

@ -1,3 +1,8 @@
2020-08-07 David Faust <david.faust@oracle.com>
* elf64-bpf.c (bpf_elf_relocate_section): Ensure signed division for
DISP16 and DISP32 relocations.
2020-08-05 David Faust <david.faust@oracle.com>
* elf64-bpf.c (bpf_elf_generic_reloc): New function.

9
bfd/elf64-bpf.c
View file

@ -442,10 +442,11 @@ bpf_elf_relocate_section (bfd *output_bfd ATTRIBUTE_UNUSED,
case R_BPF_INSN_DISP32:
{
/* Make the relocation PC-relative, and change its unit to
64-bit words. */
relocation -= sec_addr (input_section) + rel->r_offset;
/* Make it 64-bit words. */
relocation = relocation / 8;
64-bit words. Note we need *signed* arithmetic
here. */
relocation = ((bfd_signed_vma) relocation
- (sec_addr (input_section) + rel->r_offset));
relocation = (bfd_signed_vma) relocation / 8;
/* Get the addend from the instruction and apply it. */
addend = bfd_get (howto->bitsize, input_bfd,

5
ld/ChangeLog
View file

@ -1,3 +1,8 @@
2020-08-07 David Faust <david.faust@oracle.com>
* testsuite/ld-bpf/call-3.s: New file.
* testsuite/ld-bpf/call-3.d: Likewise.
2020-08-05 David Faust <david.faust@oracle.com>
* testsuite/ld-bpf/call-2.s: New file.