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[LLD][ELF][AArch64] Change the semantics of -z pac-plt.
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Summary:
Generate PAC protected plt only when "-z pac-plt" is passed to the
linker. GNU toolchain generates when it is explicitly requested[1].
When pac-plt is requested then set the GNU_PROPERTY_AARCH64_FEATURE_1_PAC
note even when not all function compiled with PAC but issue a warning.
Harmonizing the warning style for BTI/PAC/IBT.
Generate BTI protected PLT if case of "-z force-bti".

[1] https://www.sourceware.org/ml/binutils/2019-03/msg00021.html

Reviewers: peter.smith, espindola, MaskRay, grimar

Reviewed By: peter.smith, MaskRay

Subscribers: tatyana-krasnukha, emaste, arichardson, kristof.beyls, MaskRay, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D74537
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@DanielKristofKiss
DanielKristofKiss committed Feb 18, 2020
1 parent 8ffea27 commit b616262
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Showing 6 changed files with 76 additions and 42 deletions.
4 changes: 3 additions & 1 deletion lld/ELF/Arch/AArch64.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -601,8 +601,10 @@ AArch64BtiPac::AArch64BtiPac() {
// the function in an executable being taken by a shared library.
// FIXME: There is a potential optimization to omit the BTI if we detect
// that the address of the PLT entry isn't taken.
// The PAC PLT entries require dynamic loader support and this isn't known
// from properties in the objects, so we use the command line flag.
btiEntry = btiHeader && !config->shared;
pacEntry = (config->andFeatures & GNU_PROPERTY_AARCH64_FEATURE_1_PAC);
pacEntry = config->zPacPlt;

if (btiEntry || pacEntry) {
pltEntrySize = 24;
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12 changes: 7 additions & 5 deletions lld/ELF/Driver.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1736,21 +1736,23 @@ template <class ELFT> static uint32_t getAndFeatures() {
for (InputFile *f : objectFiles) {
uint32_t features = cast<ObjFile<ELFT>>(f)->andFeatures;
if (config->zForceBti && !(features & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) {
warn(toString(f) + ": -z force-bti: file does not have BTI property");
warn(toString(f) + ": -z force-bti: file does not have "
"GNU_PROPERTY_AARCH64_FEATURE_1_BTI property");
features |= GNU_PROPERTY_AARCH64_FEATURE_1_BTI;
} else if (config->zForceIbt &&
!(features & GNU_PROPERTY_X86_FEATURE_1_IBT)) {
warn(toString(f) + ": -z force-ibt: file does not have "
"GNU_PROPERTY_X86_FEATURE_1_IBT property");
features |= GNU_PROPERTY_X86_FEATURE_1_IBT;
}
if (config->zPacPlt && !(features & GNU_PROPERTY_AARCH64_FEATURE_1_PAC)) {
warn(toString(f) + ": -z pac-plt: file does not have "
"GNU_PROPERTY_AARCH64_FEATURE_1_PAC property");
features |= GNU_PROPERTY_AARCH64_FEATURE_1_PAC;
}
ret &= features;
}

// Force enable pointer authentication Plt, we don't warn in this case as
// this does not require support in the object for correctness.
if (config->zPacPlt)
ret |= GNU_PROPERTY_AARCH64_FEATURE_1_PAC;
// Force enable Shadow Stack.
if (config->zShstk)
ret |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
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2 changes: 1 addition & 1 deletion lld/ELF/SyntheticSections.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1401,7 +1401,7 @@ template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
if (config->emachine == EM_AARCH64) {
if (config->andFeatures & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)
addInt(DT_AARCH64_BTI_PLT, 0);
if (config->andFeatures & GNU_PROPERTY_AARCH64_FEATURE_1_PAC)
if (config->zPacPlt)
addInt(DT_AARCH64_PAC_PLT, 0);
}

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2 changes: 1 addition & 1 deletion lld/test/ELF/aarch64-feature-bti.s
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Original file line number Diff line number Diff line change
Expand Up @@ -174,7 +174,7 @@

# RUN: ld.lld %t.o %t2.o -z force-bti %t.so -o %tforcebti.exe 2>&1 | FileCheck --check-prefix=FORCE-WARN %s

# FORCE-WARN: aarch64-feature-bti.s.tmp2.o: -z force-bti: file does not have BTI property
# FORCE-WARN: aarch64-feature-bti.s.tmp2.o: -z force-bti: file does not have GNU_PROPERTY_AARCH64_FEATURE_1_BTI property


# RUN: llvm-readelf -n %tforcebti.exe | FileCheck --check-prefix=BTIPROP %s
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65 changes: 48 additions & 17 deletions lld/test/ELF/aarch64-feature-btipac.s
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Original file line number Diff line number Diff line change
Expand Up @@ -25,32 +25,30 @@
# BTIPACSO-NEXT: 10360: bti c
# BTIPACSO-NEXT: stp x16, x30, [sp, #-16]!
# BTIPACSO-NEXT: adrp x16, #131072
# BTIPACSO-NEXT: ldr x17, [x16, #1160]
# BTIPACSO-NEXT: add x16, x16, #1160
# BTIPACSO-NEXT: ldr x17, [x16, #1136]
# BTIPACSO-NEXT: add x16, x16, #1136
# BTIPACSO-NEXT: br x17
# BTIPACSO-NEXT: nop
# BTIPACSO-NEXT: nop
# BTIPACSO: 0000000000010380 func3@plt:
# BTIPACSO-NEXT: 10380: adrp x16, #131072
# BTIPACSO-NEXT: ldr x17, [x16, #1168]
# BTIPACSO-NEXT: add x16, x16, #1168
# BTIPACSO-NEXT: autia1716
# BTIPACSO-NEXT: ldr x17, [x16, #1144]
# BTIPACSO-NEXT: add x16, x16, #1144
# BTIPACSO-NEXT: br x17
# BTIPACSO-NEXT: nop

# BTIPACPROP: Properties: aarch64 feature: BTI, PAC

# BTIPACDYN: 0x0000000070000001 (AARCH64_BTI_PLT)
# BTIPACDYN: 0x0000000070000003 (AARCH64_PAC_PLT)
# BTIPACDYN-NOT: 0x0000000070000003 (AARCH64_PAC_PLT)

## Make an executable with both BTI and PAC properties. Expect:
## PLT[0] bti c as first instruction
## PLT[n] bti n as first instruction, autia1716 before br x17
## PLT[n] bti n as first instruction

# RUN: ld.lld %t.o %t3btipac.o %t.so -o %t.exe
# RUN: llvm-readelf -n %t.exe | FileCheck --check-prefix=BTIPACPROP %s
# RUN: llvm-objdump -d -mattr=+v8.5a --no-show-raw-insn %t.exe | FileCheck --check-prefix BTIPACEX %s
# RUN: llvm-readelf --dynamic-table %t.exe | FileCheck --check-prefix BTIPACDYN %s
# RUN: llvm-readelf --dynamic-table %t.exe | FileCheck --check-prefix BTIPACDYNEX %s

# BTIPACEX: Disassembly of section .text:
# BTIPACEX: 0000000000210370 func1:
Expand All @@ -64,19 +62,21 @@
# BTIPACEX-NEXT: 210380: bti c
# BTIPACEX-NEXT: stp x16, x30, [sp, #-16]!
# BTIPACEX-NEXT: adrp x16, #131072
# BTIPACEX-NEXT: ldr x17, [x16, #1208]
# BTIPACEX-NEXT: add x16, x16, #1208
# BTIPACEX-NEXT: ldr x17, [x16, #1192]
# BTIPACEX-NEXT: add x16, x16, #1192
# BTIPACEX-NEXT: br x17
# BTIPACEX-NEXT: nop
# BTIPACEX-NEXT: nop
# BTIPACEX: 00000000002103a0 func2@plt:
# BTIPACEX-NEXT: 2103a0: bti c
# BTIPACEX-NEXT: adrp x16, #131072
# BTIPACEX-NEXT: ldr x17, [x16, #1216]
# BTIPACEX-NEXT: add x16, x16, #1216
# BTIPACEX-NEXT: autia1716
# BTIPACEX-NEXT: ldr x17, [x16, #1200]
# BTIPACEX-NEXT: add x16, x16, #1200
# BTIPACEX-NEXT: br x17

# BTIPACDYNEX: 0x0000000070000001 (AARCH64_BTI_PLT)
# BTIPACDYNEX-NOT: 0x0000000070000003 (AARCH64_PAC_PLT)

## Check that combinations of BTI+PAC with 0 properties results in standard PLT

# RUN: ld.lld %t.o %t3.o %t.so -o %t.exe
Expand Down Expand Up @@ -112,14 +112,17 @@
## Check that combination of -z pac-plt and -z force-bti warns for the file that
## doesn't contain the BTI property, but generates PAC and BTI PLT sequences.
## The -z pac-plt doesn't warn as it is not required for correctness.
## Expect:
## PLT[0] bti c as first instruction
## PLT[n] bti n as first instruction, autia1716 before br x17

# RUN: ld.lld %t.o %t3.o %t.so -z pac-plt -z force-bti -o %t.exe 2>&1 | FileCheck --check-prefix=FORCE-WARN %s

# FORCE-WARN: aarch64-feature-btipac.s.tmp3.o: -z force-bti: file does not have BTI property
# FORCE-WARN: aarch64-feature-btipac.s.tmp3.o: -z force-bti: file does not have GNU_PROPERTY_AARCH64_FEATURE_1_BTI property

# RUN: llvm-readelf -n %t.exe | FileCheck --check-prefix=BTIPACPROP %s
# RUN: llvm-objdump -d -mattr=+v8.5a --no-show-raw-insn %t.exe | FileCheck --check-prefix BTIPACEX %s
# RUN: llvm-readelf --dynamic-table %t.exe | FileCheck --check-prefix BTIPACDYN %s
# RUN: llvm-objdump -d -mattr=+v8.5a --no-show-raw-insn %t.exe | FileCheck --check-prefix BTIPACEX2 %s
# RUN: llvm-readelf --dynamic-table %t.exe | FileCheck --check-prefix BTIPACDYN2 %s
.section ".note.gnu.property", "a"
.long 4
.long 0x10
Expand All @@ -140,3 +143,31 @@ func1:
.globl func3
.type func3,%function
ret

# BTIPACEX2: Disassembly of section .text:
# BTIPACEX2: 0000000000210370 func1:
# BTIPACEX2-NEXT: 210370: bl #48 <func2@plt>
# BTIPACEX2-NEXT: ret
# BTIPACEX2-NEXT: ret
# BTIPACEX2: 000000000021037c func3:
# BTIPACEX2-NEXT: 21037c: ret
# BTIPACEX2: Disassembly of section .plt:
# BTIPACEX2: 0000000000210380 .plt:
# BTIPACEX2-NEXT: 210380: bti c
# BTIPACEX2-NEXT: stp x16, x30, [sp, #-16]!
# BTIPACEX2-NEXT: adrp x16, #131072
# BTIPACEX2-NEXT: ldr x17, [x16, #1208]
# BTIPACEX2-NEXT: add x16, x16, #1208
# BTIPACEX2-NEXT: br x17
# BTIPACEX2-NEXT: nop
# BTIPACEX2-NEXT: nop
# BTIPACEX2: 00000000002103a0 func2@plt:
# BTIPACEX2-NEXT: 2103a0: bti c
# BTIPACEX2-NEXT: adrp x16, #131072
# BTIPACEX2-NEXT: ldr x17, [x16, #1216]
# BTIPACEX2-NEXT: add x16, x16, #1216
# BTIPACEX2-NEXT: autia1716
# BTIPACEX2-NEXT: br x17

# BTIPACDYN2: 0x0000000070000001 (AARCH64_BTI_PLT)
# BTIPACDYN2-NEXT: 0x0000000070000003 (AARCH64_PAC_PLT)
33 changes: 16 additions & 17 deletions lld/test/ELF/aarch64-feature-pac.s
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,10 @@
# NOPAC-NEXT: add x16, x16, #968
# NOPAC-NEXT: br x17

# SOGOTPLT: Hex dump of section '.got.plt':
# SOGOTPLT-NEXT: 0x000303b0 00000000 00000000 00000000 00000000
# SOGOTPLT-NEXT: 0x000303c0 00000000 00000000 d0020100 00000000

# NOPACDYN-NOT: 0x0000000070000001 (AARCH64_BTI_PLT)
# NOPACDYN-NOT: 0x0000000070000003 (AARCH64_PAC_PLT)

Expand All @@ -41,9 +45,7 @@
# RUN: llvm-readelf -x .got.plt %t.so | FileCheck --check-prefix SOGOTPLT2 %s
# RUN: llvm-readelf --dynamic-table %t.so | FileCheck --check-prefix PACDYN %s

## PAC has no effect on PLT[0], for PLT[N] autia1716 is used to authenticate
## the address in x17 (context in x16) before branching to it. The dynamic
## loader is responsible for calling pacia1716 on the entry.
## PAC has no effect on PLT[0], for PLT[N].
# PACSO: 0000000000010348 func2:
# PACSO-NEXT: 10348: bl #56 <func3@plt>
# PACSO-NEXT: ret
Expand All @@ -53,32 +55,26 @@
# PACSO: 0000000000010360 .plt:
# PACSO-NEXT: 10360: stp x16, x30, [sp, #-16]!
# PACSO-NEXT: adrp x16, #131072
# PACSO-NEXT: ldr x17, [x16, #1144]
# PACSO-NEXT: add x16, x16, #1144
# PACSO-NEXT: ldr x17, [x16, #1120]
# PACSO-NEXT: add x16, x16, #1120
# PACSO-NEXT: br x17
# PACSO-NEXT: nop
# PACSO-NEXT: nop
# PACSO-NEXT: nop
# PACSO: 0000000000010380 func3@plt:
# PACSO-NEXT: 10380: adrp x16, #131072
# PACSO-NEXT: ldr x17, [x16, #1152]
# PACSO-NEXT: add x16, x16, #1152
# PACSO-NEXT: autia1716
# PACSO-NEXT: ldr x17, [x16, #1128]
# PACSO-NEXT: add x16, x16, #1128
# PACSO-NEXT: br x17
# PACSO-NEXT: nop

# SOGOTPLT: Hex dump of section '.got.plt':
# SOGOTPLT-NEXT: 0x000303b0 00000000 00000000 00000000 00000000
# SOGOTPLT-NEXT: 0x000303c0 00000000 00000000 d0020100 00000000

# SOGOTPLT2: Hex dump of section '.got.plt':
# SOGOTPLT2-NEXT: 0x00030468 00000000 00000000 00000000 00000000
# SOGOTPLT2-NEXT: 0x00030478 00000000 00000000 60030100 00000000
# SOGOTPLT2-NEXT: 0x00030450 00000000 00000000 00000000 00000000
# SOGOTPLT2-NEXT: 0x00030460 00000000 00000000 60030100 00000000

# PACPROP: Properties: aarch64 feature: PAC

# PACDYN-NOT: 0x0000000070000001 (AARCH64_BTI_PLT)
# PACDYN: 0x0000000070000003 (AARCH64_PAC_PLT)
# PACDYN-NOT: 0x0000000070000003 (AARCH64_PAC_PLT)

## Turn on PAC entries with the -z pac-plt command line option. There are no
## warnings in this case as the choice to use PAC in PLT entries is orthogonal
Expand All @@ -87,7 +83,7 @@

# RUN: ld.lld %t.o %t2.o -z pac-plt %t.so -o %tpacplt.exe
# RUN: llvm-readelf -n %tpacplt.exe | FileCheck --check-prefix=PACPROP %s
# RUN: llvm-readelf --dynamic-table %tpacplt.exe | FileCheck --check-prefix PACDYN %s
# RUN: llvm-readelf --dynamic-table %tpacplt.exe | FileCheck --check-prefix PACDYN2 %s
# RUN: llvm-objdump -d -mattr=+v8.3a --no-show-raw-insn %tpacplt.exe | FileCheck --check-prefix PACPLT %s

# PACPLT: Disassembly of section .text:
Expand All @@ -114,6 +110,9 @@
# PACPLT-NEXT: br x17
# PACPLT-NEXT: nop

# PACDYN2-NOT: 0x0000000070000001 (AARCH64_BTI_PLT)
# PACDYN2: 0x0000000070000003 (AARCH64_PAC_PLT)

.section ".note.gnu.property", "a"
.long 4
.long 0x10
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