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[LLD] Extend special OpenBSD support, but scope under ELFOSABI #97122

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Merged
merged 1 commit into from
Jul 12, 2024
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[LLD] Extend special OpenBSD support, but scope under ELFOSABI #97122

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2 changes: 2 additions & 0 deletions lld/ELF/ScriptParser.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1628,7 +1628,9 @@ unsigned ScriptParser::readPhdrType() {
.Case("PT_GNU_EH_FRAME", PT_GNU_EH_FRAME)
.Case("PT_GNU_STACK", PT_GNU_STACK)
.Case("PT_GNU_RELRO", PT_GNU_RELRO)
.Case("PT_OPENBSD_MUTABLE", PT_OPENBSD_MUTABLE)
.Case("PT_OPENBSD_RANDOMIZE", PT_OPENBSD_RANDOMIZE)
.Case("PT_OPENBSD_SYSCALLS", PT_OPENBSD_SYSCALLS)
.Case("PT_OPENBSD_WXNEEDED", PT_OPENBSD_WXNEEDED)
.Case("PT_OPENBSD_BOOTDATA", PT_OPENBSD_BOOTDATA)
.Default(-1);
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34 changes: 26 additions & 8 deletions lld/ELF/Writer.cpp
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Expand Up @@ -601,10 +601,16 @@ static bool isRelroSection(const OutputSection *sec) {
// ELF in spirit. But in reality many linker features depend on
// magic section names.
StringRef s = sec->name;
return s == ".data.rel.ro" || s == ".bss.rel.ro" || s == ".ctors" ||
s == ".dtors" || s == ".jcr" || s == ".eh_frame" ||
s == ".fini_array" || s == ".init_array" ||
s == ".openbsd.randomdata" || s == ".preinit_array";

bool abiAgnostic = s == ".data.rel.ro" || s == ".bss.rel.ro" ||
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It should be fine to keep this unchanged. We can add the osabi check if the .openbsd.* list ever gets longer.

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@Ericson2314 Ericson2314 Jul 12, 2024 •
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@MaskRay I would sort of like to change it for consistency.

I ended up duplicating the test I had to change so we have a Linux and OpenBSD version, and this makes me feel better about coverage, etc.

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(And checked locally that both the new tests worked, and the old test failed.)

s == ".ctors" || s == ".dtors" || s == ".jcr" ||
s == ".eh_frame" || s == ".fini_array" ||
s == ".init_array" || s == ".preinit_array";

bool abiSpecific =
config->osabi == ELFOSABI_OPENBSD && s == ".openbsd.randomdata";

return abiAgnostic || abiSpecific;
}

// We compute a rank for each section. The rank indicates where the
Expand Down Expand Up @@ -2273,10 +2279,22 @@ SmallVector<PhdrEntry *, 0> Writer<ELFT>::createPhdrs(Partition &part) {
addHdr(PT_GNU_EH_FRAME, part.ehFrameHdr->getParent()->getPhdrFlags())
->add(part.ehFrameHdr->getParent());

// PT_OPENBSD_RANDOMIZE is an OpenBSD-specific feature. That makes
// the dynamic linker fill the segment with random data.
if (OutputSection *cmd = findSection(".openbsd.randomdata", partNo))
addHdr(PT_OPENBSD_RANDOMIZE, cmd->getPhdrFlags())->add(cmd);
if (config->osabi == ELFOSABI_OPENBSD) {
// PT_OPENBSD_MUTABLE makes the dynamic linker fill the segment with
// zero data, like bss, but it can be treated differently.
if (OutputSection *cmd = findSection(".openbsd.mutable", partNo))
addHdr(PT_OPENBSD_MUTABLE, cmd->getPhdrFlags())->add(cmd);

// PT_OPENBSD_RANDOMIZE makes the dynamic linker fill the segment
// with random data.
if (OutputSection *cmd = findSection(".openbsd.randomdata", partNo))
addHdr(PT_OPENBSD_RANDOMIZE, cmd->getPhdrFlags())->add(cmd);

// PT_OPENBSD_SYSCALLS makes the kernel and dynamic linker register
// system call sites.
if (OutputSection *cmd = findSection(".openbsd.syscalls", partNo))
addHdr(PT_OPENBSD_SYSCALLS, cmd->getPhdrFlags())->add(cmd);
}

if (config->zGnustack != GnuStackKind::None) {
// PT_GNU_STACK is a special section to tell the loader to make the
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8 changes: 6 additions & 2 deletions lld/test/ELF/openbsd-phdr.s
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@@ -1,10 +1,10 @@
# REQUIRES: x86
# RUN: rm -rf %t && split-file %s %t && cd %t
# RUN: llvm-mc -filetype=obj -triple=x86_64 randomdata.s -o randomdata.o
# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-openbsd randomdata.s -o randomdata.o
# RUN: ld.lld randomdata.o -o randomdata
# RUN: llvm-readelf -S -l randomdata | FileCheck %s --check-prefix=RANDOMDATA

# RUN: llvm-mc -filetype=obj -triple=x86_64 /dev/null -o wxneeded.o
# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-openbsd /dev/null -o wxneeded.o
# RUN: ld.lld -z wxneeded wxneeded.o -o wxneeded
# RUN: llvm-readelf -l wxneeded | FileCheck %s --check-prefix=WXNEEDED

Expand All @@ -20,6 +20,8 @@
# RANDOMDATA: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
# RANDOMDATA: OPENBSD_RANDOMIZE 0x[[O]] 0x[[ADDR]] 0x[[ADDR]] 0x000008 0x000008 R 0x1
# CHECK-NEXT: OPENBSD_BOOTDATA 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 R 0
# CHECK-NEXT: OPENBSD_MUTABLE 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 R 0
# CHECK-NEXT: OPENBSD_SYSCALLS 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 R 0
# CHECK-NEXT: OPENBSD_WXNEEDED 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 R 0

#--- randomdata.s
Expand All @@ -31,6 +33,8 @@ PHDRS {
text PT_LOAD FILEHDR PHDRS;
rand PT_OPENBSD_RANDOMIZE;
boot PT_OPENBSD_BOOTDATA;
mutable PT_OPENBSD_MUTABLE;
syscalls PT_OPENBSD_SYSCALLS;
wxneeded PT_OPENBSD_WXNEEDED;
}
SECTIONS {
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46 changes: 46 additions & 0 deletions lld/test/ELF/relro-openbsd.s
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Original file line number Diff line number Diff line change
@@ -0,0 +1,46 @@
// REQUIRES: x86

// RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-openbsd %s -o %t.o
// RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-openbsd %p/Inputs/shared.s -o %t2.o
// RUN: ld.lld -shared %t2.o -o %t2.so

// RUN: ld.lld %t.o %t2.so -z now -z norelro -z relro -o %t
// RUN: llvm-readelf -l %t | FileCheck --check-prefix=CHECK --check-prefix=FULLRELRO %s

// RUN: ld.lld %t.o %t2.so -z norelro -z relro -o %t
// RUN: llvm-readelf -l %t | FileCheck --check-prefix=CHECK --check-prefix=PARTRELRO %s

// RUN: ld.lld %t.o %t2.so -z norelro -o %t
// RUN: llvm-readelf -l %t | FileCheck --check-prefix=NORELRO %s

// CHECK: Program Headers:
// CHECK-NEXT: Type
// CHECK-NEXT: PHDR
// CHECK-NEXT: LOAD
// CHECK-NEXT: LOAD
// CHECK-NEXT: LOAD
// CHECK-NEXT: LOAD
// CHECK-NEXT: DYNAMIC
// CHECK-NEXT: GNU_RELRO
// CHECK: Section to Segment mapping:

// FULLRELRO: 03 .openbsd.randomdata .dynamic .got .got.plt .relro_padding {{$}}
// PARTRELRO: 03 .openbsd.randomdata .dynamic .got .relro_padding {{$}}


// NORELRO-NOT: GNU_RELRO

.global _start
_start:
.long bar
jmp *bar2@GOTPCREL(%rip)

.section .data,"aw"
.quad 0

.zero 4
.section .foo,"aw"
.section .bss,"",@nobits

.section .openbsd.randomdata, "aw"
.quad 0
6 changes: 3 additions & 3 deletions lld/test/ELF/relro.s
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Expand Up @@ -24,8 +24,8 @@
// CHECK-NEXT: GNU_RELRO
// CHECK: Section to Segment mapping:

// FULLRELRO: 03 .openbsd.randomdata .dynamic .got .got.plt .relro_padding {{$}}
// PARTRELRO: 03 .openbsd.randomdata .dynamic .got .relro_padding {{$}}
// FULLRELRO: 03 .data.rel.ro .dynamic .got .got.plt .relro_padding {{$}}
// PARTRELRO: 03 .data.rel.ro .dynamic .got .relro_padding {{$}}


// NORELRO-NOT: GNU_RELRO
Expand All @@ -42,5 +42,5 @@ _start:
.section .foo,"aw"
.section .bss,"",@nobits

.section .openbsd.randomdata, "aw"
.section .data.rel.ro, "aw"
.quad 0
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