112 lines
4.3 KiB
Text
112 lines
4.3 KiB
Text
- Merge '.openbsd.randomdata.*' sections into a single '.openbsd.randomdata'
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section when linking, as we do when using ld from binutils.
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- Generate __data_start symbol that marks the start of .data when __data_start
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is referenced from code being linked.
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- Put .got.plt in RELRO.
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- On i386, produce binaries that are compatible with our W^X implementation.
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- In the linkers, collect objects in section "openbsd.mutable" and place
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them into a page-aligned region in the bss, with the right markers for
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kernel/ld.so to identify the region and skip making it immutable.
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- Implement support for PT_OPENBSD_NOBTCFI in lld(1). This can be set using
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the -z nobtcfi option.
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Index: tools/lld/ELF/Writer.cpp
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--- tools/lld/ELF/Writer.cpp.orig
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+++ tools/lld/ELF/Writer.cpp
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@@ -145,7 +145,8 @@ StringRef elf::getOutputSectionName(const InputSection
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for (StringRef v :
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{".text.", ".rodata.", ".data.rel.ro.", ".data.", ".bss.rel.ro.",
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".bss.", ".init_array.", ".fini_array.", ".ctors.", ".dtors.", ".tbss.",
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- ".gcc_except_table.", ".tdata.", ".ARM.exidx.", ".ARM.extab."})
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+ ".gcc_except_table.", ".tdata.", ".ARM.exidx.", ".ARM.extab.",
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+ ".openbsd.randomdata.", ".openbsd.mutable." })
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if (isSectionPrefix(v, s->name))
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return v.drop_back();
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@@ -324,6 +325,7 @@ void elf::addReservedSymbols() {
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};
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ElfSym::bss = add("__bss_start", 0);
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+ ElfSym::data = add("__data_start", 0);
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ElfSym::end1 = add("end", -1);
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ElfSym::end2 = add("_end", -1);
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ElfSym::etext1 = add("etext", -1);
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@@ -883,7 +885,11 @@ static bool isRelroSection(const OutputSection *sec) {
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// However, if "-z now" is given, the lazy symbol resolution is
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// disabled, which enables us to put it into RELRO.
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if (sec == in.gotPlt->getParent())
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+#ifndef __OpenBSD__
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return config->zNow;
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+#else
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+ return true; /* kbind(2) means we can always put these in RELRO */
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+#endif
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// .dynamic section contains data for the dynamic linker, and
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// there's no need to write to it at runtime, so it's better to put
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@@ -1193,6 +1199,9 @@ template <class ELFT> void Writer<ELFT>::setReservedSy
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if (ElfSym::bss)
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ElfSym::bss->section = findSection(".bss");
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+ if (ElfSym::data)
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+ ElfSym::data->section = findSection(".data");
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+
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// Setup MIPS _gp_disp/__gnu_local_gp symbols which should
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// be equal to the _gp symbol's value.
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if (ElfSym::mipsGp) {
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@@ -2461,6 +2470,12 @@ std::vector<PhdrEntry *> Writer<ELFT>::createPhdrs(Par
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addHdr(PT_GNU_EH_FRAME, part.ehFrameHdr->getParent()->getPhdrFlags())
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->add(part.ehFrameHdr->getParent());
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+ // PT_OPENBSD_MUTABLE is an OpenBSD-specific feature. That makes
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+ // the dynamic linker fill the segment with zero data, like bss, but
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+ // it can be treated differently.
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+ if (OutputSection *cmd = findSection(".openbsd.mutable", partNo))
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+ addHdr(PT_OPENBSD_MUTABLE, cmd->getPhdrFlags())->add(cmd);
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+
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// PT_OPENBSD_RANDOMIZE is an OpenBSD-specific feature. That makes
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// the dynamic linker fill the segment with random data.
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if (OutputSection *cmd = findSection(".openbsd.randomdata", partNo))
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@@ -2484,6 +2499,11 @@ std::vector<PhdrEntry *> Writer<ELFT>::createPhdrs(Par
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if (config->zWxneeded)
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addHdr(PT_OPENBSD_WXNEEDED, PF_X);
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+ // PT_OPENBSD_NOBTCFI is an OpenBSD-specific header to mark that the
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+ // executable is expected to violate branch-target CFI checks.
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+ if (config->zNoBtCfi)
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+ addHdr(PT_OPENBSD_NOBTCFI, PF_X);
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+
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if (OutputSection *cmd = findSection(".note.gnu.property", partNo))
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addHdr(PT_GNU_PROPERTY, PF_R)->add(cmd);
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@@ -2576,6 +2596,31 @@ template <class ELFT> void Writer<ELFT>::fixSectionAli
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};
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}
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};
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+
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+#ifdef __OpenBSD__
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+ // On i386, produce binaries that are compatible with our W^X implementation
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+ if (config->emachine == EM_386) {
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+ auto NXAlign = [](OutputSection *Cmd) {
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+ if (Cmd && !Cmd->addrExpr)
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+ Cmd->addrExpr = [=] {
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+ return alignTo(script->getDot(), 0x20000000);
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+ };
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+ };
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+
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+ for (Partition &part : partitions) {
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+ PhdrEntry *firstRW = nullptr;
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+ for (PhdrEntry *P : part.phdrs) {
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+ if (P->p_type == PT_LOAD && (P->p_flags & PF_W)) {
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+ firstRW = P;
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+ break;
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+ }
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+ }
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+
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+ if (firstRW)
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+ NXAlign(firstRW->firstSec);
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+ }
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+ }
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+#endif
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for (Partition &part : partitions) {
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prev = nullptr;
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