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Fixes for static PIE executables #166

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Fixes for static PIE executables #166

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c3ffe62
rewriteSectionsLibrary: assume all libraries may be executable; fixes…
rcombs Jun 16, 2020
5daa357
modifyRPath: when possible, avoid growing the dynamic section
Mar 30, 2019
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25 changes: 15 additions & 10 deletions src/patchelf.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -106,8 +106,6 @@ class ElfFile

bool changed = false;

bool isExecutable = false;

typedef std::string SectionName;
typedef std::map<SectionName, std::string> ReplacedSections;

Expand Down Expand Up @@ -415,10 +413,8 @@ ElfFile<ElfFileParamNames>::ElfFile(FileContents fileContents)
error("program headers have wrong size");

/* Copy the program and section headers. */
for (int i = 0; i < rdi(hdr->e_phnum); ++i) {
for (int i = 0; i < rdi(hdr->e_phnum); ++i)
phdrs.push_back(* ((Elf_Phdr *) (contents + rdi(hdr->e_phoff)) + i));
if (rdi(phdrs[i].p_type) == PT_INTERP) isExecutable = true;
}

for (int i = 0; i < rdi(hdr->e_shnum); ++i)
shdrs.push_back(* ((Elf_Shdr *) (contents + rdi(hdr->e_shoff)) + i));
Expand Down Expand Up @@ -741,10 +737,9 @@ void ElfFile<ElfFileParamNames>::rewriteSectionsLibrary()
since DYN executables tend to start at virtual address 0, so
rewriteSectionsExecutable() won't work because it doesn't have
any virtual address space to grow downwards into. */
if (isExecutable && startOffset > startPage) {
if (startOffset > startPage)
debug("shifting new PT_LOAD segment by %d bytes to work around a Linux kernel bug\n", startOffset - startPage);
startPage = startOffset;
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This disables this mitigation?

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no, it unconditionally applies it...

}
startPage = startOffset;
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I understand why isExecutable was removed as a conditional but not why startPage = startOffset was moved out.


/* Add a segment that maps the replaced sections into memory. */
wri(hdr->e_phoff, sizeof(Elf_Ehdr));
Expand Down Expand Up @@ -1147,7 +1142,7 @@ void ElfFile<ElfFileParamNames>::modifyRPath(RPathOp op,
string. */
std::vector<std::string> neededLibs;
Elf_Dyn * dyn = (Elf_Dyn *) (contents + rdi(shdrDynamic.sh_offset));
Elf_Dyn * dynRPath = 0, * dynRunPath = 0;
Elf_Dyn * dynRPath = 0, * dynRunPath = 0, * dynReplaceable = 0;
char * rpath = 0;
for ( ; rdi(dyn->d_tag) != DT_NULL; dyn++) {
if (rdi(dyn->d_tag) == DT_RPATH) {
Expand All @@ -1162,6 +1157,12 @@ void ElfFile<ElfFileParamNames>::modifyRPath(RPathOp op,
}
else if (rdi(dyn->d_tag) == DT_NEEDED)
neededLibs.push_back(std::string(strTab + rdi(dyn->d_un.d_val)));
/* Try to replace an IGNORE rather than growing and moving the section, if possible */
else if (rdi(dyn->d_tag) == DT_IGNORE)
dynReplaceable = dyn;
/* If we don't find an IGNORE, RELCOUNT/RELACOUNT are redundant and optional, so we can replace those */
else if (!dynReplaceable && (rdi(dyn->d_tag) == DT_RELCOUNT || rdi(dyn->d_tag) == DT_RELACOUNT))
dynReplaceable = dyn;
}

if (op == rpPrint) {
Expand Down Expand Up @@ -1288,7 +1289,11 @@ void ElfFile<ElfFileParamNames>::modifyRPath(RPathOp op,
if (dynRunPath) dynRunPath->d_un.d_val = shdrDynStr.sh_size;
if (dynRPath) dynRPath->d_un.d_val = shdrDynStr.sh_size;
}

/* Convert an unused or redundant entry to a DT_RPATH or DT_RUNPATH */
else if (dynReplaceable) {
dynReplaceable->d_un.d_val = shdrDynStr.sh_size;
dynReplaceable->d_tag = forceRPath ? DT_RPATH : DT_RUNPATH;
}
else {
/* There is no DT_RUNPATH entry in the .dynamic section, so we
have to grow the .dynamic section. */
Expand Down