diff options
Diffstat (limited to 'src/model/insert.c')
-rw-r--r-- | src/model/insert.c | 111 |
1 files changed, 111 insertions, 0 deletions
diff --git a/src/model/insert.c b/src/model/insert.c new file mode 100644 index 0000000..2086c6e --- /dev/null +++ b/src/model/insert.c @@ -0,0 +1,111 @@ +#include <assert.h> +#include <sys/types.h> +#include <gelf.h> +#include <libelfu/libelfu.h> + + + +/* + * Insert space at a given position in the file by moving everything + * after it towards the end of the file, and everything before it + * towards lower memory regions where it is mapped. + * + * off must not be in the middle of any data structure, such as + * PHDRs, SHDRs, or sections. Behaviour is undefined if it is. + * + * PHDRs will be patched such that everything AFTER off is mapped to + * the same address in memory, and everything BEFORE it is shifted to + * lower addresses, making space for the new data in-between. + */ +GElf_Xword elfu_mInsertBefore(ElfuElf *me, GElf_Off off, GElf_Xword size) +{ + ElfuScn *ms; + ElfuPhdr *mp; + + assert(me); + + // TODO: Take p_align into account + + /* Move SHDRs and PHDRs */ + if (me->ehdr.e_shoff >= off) { + me->ehdr.e_shoff += size; + } + + if (me->ehdr.e_phoff >= off) { + me->ehdr.e_phoff += size; + } + + /* Patch PHDRs to include new data */ + CIRCLEQ_FOREACH(mp, &me->phdrList, elem) { + GElf_Off end = mp->phdr.p_offset + mp->phdr.p_filesz; + + if (mp->phdr.p_offset >= off) { + /* Insertion before PHDR's content, so it's just shifted */ + mp->phdr.p_offset += size; + } else { + /* mp->phdr.p_offset < off */ + + if (off < end) { + /* Mark this as a modified area */ + + /* Insertion in the middle of PHDR, so let it span the new data */ + mp->phdr.p_filesz += size; + mp->phdr.p_memsz += size; + mp->phdr.p_vaddr -= size; + mp->phdr.p_paddr -= size; + } else { + /* Insertion after PHDR's content, so it may need to be + remapped. This will happen in a second pass. + */ + } + } + } + + /* For each LOAD header, find clashing headers that need to be + remapped to lower memory areas. + */ + CIRCLEQ_FOREACH(mp, &me->phdrList, elem) { + if (mp->phdr.p_type == PT_LOAD) { + ElfuPhdr *mp2; + + CIRCLEQ_FOREACH(mp2, &me->phdrList, elem) { + if (mp2->phdr.p_type != PT_LOAD + && mp2->phdr.p_offset + mp2->phdr.p_filesz <= off) { + /* The PHDR ends in the file before the injection site */ + GElf_Off vend1 = mp->phdr.p_vaddr + mp->phdr.p_memsz; + GElf_Off pend1 = mp->phdr.p_paddr + mp->phdr.p_memsz; + GElf_Off vend2 = mp2->phdr.p_vaddr + mp2->phdr.p_memsz; + GElf_Off pend2 = mp2->phdr.p_paddr + mp2->phdr.p_memsz; + + /* If mp and mp2 now overlap in memory */ + if ((mp2->phdr.p_vaddr < vend1 && vend2 > mp->phdr.p_vaddr) + || (mp2->phdr.p_paddr < pend1 && pend2 > mp->phdr.p_paddr)) { + /* Move mp2 down in memory, as mp has been resized. + Maintaining the relative offset between them is the best + guess at maintaining consistency. + */ + mp2->phdr.p_vaddr -= size; + mp2->phdr.p_paddr -= size; + } + } + } + } + } + + /* Move the sections themselves */ + CIRCLEQ_FOREACH(ms, &me->scnList, elem) { + if (ms->shdr.sh_offset >= off) { + ms->shdr.sh_offset += size; + } else { + /* sh_offset < off */ + + /* If this was in a LOAD segment, it has been adjusted there + and this synchronises it. + If not, it doesn't matter anyway. + */ + ms->shdr.sh_addr -= size; + } + } + + return size; +} |