Add program property and PLT for CFI extension #417

kito-cheng · 2024-01-04T08:27:16Z

We introduce .note.gnu.property section to store infomations that linker or runtime system may use, and we define two bit for landing pad and shadow stack.

Those two bit will checked by loader - and use that info to enable the landing pad checking and/or shadow stack feature.

kito-cheng · 2024-01-04T08:28:07Z

cc @ved-rivos

riscv-elf.adoc

rui314 · 2024-01-05T07:40:53Z

My concern about this proposal is that, with the 32-bit bitmap, we can't have more than 32 extensions. That might be OK for x86-64 that is controlled only by Intel and AMD, but it is likely that we would have way more extensions than x86-64 for RISC-V. I'm not sure even 64 bits is enough. Maybe we should avoid the bitmap completely?

kito-cheng · 2024-01-05T08:06:15Z

@rui314
GNU property is kind of key-value structure, key is 32 bit integer, and we have 536,870,912 can use for the key per the definition of GNU_PROPERTY_LOPROC and GNU_PROPERTY_HIPROC.

/* Processor-specific semantics, lo */
#define GNU_PROPERTY_LOPROC                     0xc0000000
/* Processor-specific semantics, hi */
#define GNU_PROPERTY_HIPROC                     0xdfffffff

So we have 536,870,912 * 32 rather than only 32-bit bitmap :)

rui314 · 2024-01-05T08:58:39Z

@kito-cheng Ah, you are right. Even though I've implemented the feature to the linker, I forgot the actual on-file format. Thank you for pointing that out!

MaskRay · 2024-01-08T00:43:22Z

Thanks for the proposal. On Arm/x86, if all relocatable files contain .note.gnu.property (which contains NT_GNU_PROPERTY_TYPE_0 notes) with the GNU_PROPERTY_X86_FEATURE_1_IBT bit set, the linker will mark the output as compatible with the feature. Assembly files often lack .note.gnu.property, making the CFI features difficult to deploy...

That said, this is most viable proposal. Defining GNU program property looks good for x86/Arm parity.

You may want to mention that n_type is NT_GNU_PROPERTY_TYPE_0.

Add property for CFI extension

"property" is a heavily overloaded term. Consider "program property" or just use .note.gnu.property to be more specific.

sorear · 2024-02-18T18:43:13Z

@kito-cheng Isn't the usefulness of this degraded by the fact that we only allocate 1 32-bit property instead of the ~ 3 * 32768 allocated on x86? When we start to use the next bitmap, an old linker won't be able to propagate it, and so on.

We introduce .note.gnu.property section to store infomations that linker or runtime system may use, and we define 4 program property classes to specifying the merge semantics, it's used for forward compatibility in linker implementations, allowing linker can correctly handle program property types even if they are not recognized. We don't define any program property within this PR, it would be separate PR like #417

kito-cheng · 2024-02-26T09:03:06Z

Split base program property part into #428

We introduce .note.gnu.property section to store infomations that linker or runtime system may use, and we define 4 program property classes to specifying the merge semantics, it's used for forward compatibility in linker implementations, allowing linker can correctly handle program property types even if they are not recognized. We don't define any program property within this PR, it would be separate PR like #417

kito-cheng · 2024-02-26T09:59:23Z

ChangeLog:

Based on Add program property #428
Rename GNU_PROPERTY_RISCV_FEATURE_1_ZICFILP to GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_SIMPLE
Rename GNU_PROPERTY_RISCV_FEATURE_1_ZICFISS to GNU_PROPERTY_RISCV_FEATURE_1_CFI_SS
Explicitly specify the labeling scheme in GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_SIMPLE, label will always set to 1.

riscv-elf.adoc

kito-cheng · 2024-02-26T13:52:18Z

Changes:

Explicitly specify the labeling scheme in GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_SIMPLE, label will always set to 0.
Add simple landing pad PLT.
Add DT_RISCV_SIMPLE_LP_PLT to mark this object use simple landing pad PLT.

We introduce .note.gnu.property section to store infomations that linker or runtime system may use, and we define 4 program property classes to specifying the merge semantics, it's used for forward compatibility in linker implementations, allowing linker can correctly handle program property types even if they are not recognized. We don't define any program property within this PR, it would be separate PR like #417

Define two bit for landing pad and shadow stack, and we plan to defined third bit `GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_COMPLEX` for complex labeling scheme.

Changes: - Rename `GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_SIMPLE` to `GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_UNLABELED` - Fix wrong offset in the first PLT stubs for the simple landing pad PLT.

kito-cheng · 2024-07-17T08:03:15Z

Changes:

Rename GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_SIMPLE to GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_UNLABELED
Fix wrong offset in the first PLT stubs for the simple landing pad PLT.

This patch implements simple landing pad labels [0]. When Zicfilp enabled, this patch inserts `lpad 0` at the beginning of basic blocks which are possible to be landed by indirect jumps. This patch also supports option riscv-landing-pad-label to make users cpable to set nonzero fixed labels. Using nonzero fixed label force setting t2 before indirect jumps. It's less portable but more strict than original implementation. [0]: riscv-non-isa/riscv-elf-psabi-doc#417

This is cherry-picked from upstream pr #91860. This patch is based on #91855. This patch inserts simple landing pad ([pr])before indirct jumps. And also make option riscv-landing-pad-label influence this feature. [pr]: riscv-non-isa/riscv-elf-psabi-doc#417

This patch implements simple landing pad labels [0]. When Zicfilp enabled, this patch inserts `lpad 0` at the beginning of basic blocks which are possible to be landed by indirect jumps. This patch also supports option riscv-landing-pad-label to make users cpable to set nonzero fixed labels. Using nonzero fixed label force setting t2 before indirect jumps. It's less portable but more strict than original implementation. [0]: riscv-non-isa/riscv-elf-psabi-doc#417

This patch is based on llvm#91855. This patch inserts simple landing pad ([pr])before indirct jumps. And also make option riscv-landing-pad-label influence this feature. [pr]: riscv-non-isa/riscv-elf-psabi-doc#417

This patch implements simple landing pad labels ([pr]). When Zicfilp enabled, this patch inserts `lpad 0` at the beginning of basic blocks which are possible to be landed by indirect jumps. This patch also supports option riscv-landing-pad-label to make users cpable to set nonzero fixed labels. Using nonzero fixed label force setting t2 before indirect jumps. It's less portable but more strict than original implementation. [pr]: riscv-non-isa/riscv-elf-psabi-doc#417

This patch is based on llvm#91855. This patch inserts simple landing pad ([pr])before indirct jumps. And also make option riscv-landing-pad-label influence this feature. [pr]: riscv-non-isa/riscv-elf-psabi-doc#417

…91860) This patch is based on #91855. This patch inserts simple landing pad ([pr])before indirct jumps. And this also make option riscv-landing-pad-label influence this feature. [pr]: riscv-non-isa/riscv-elf-psabi-doc#417

kito-cheng · 2025-02-24T14:31:40Z

We have implementation on both toolchain, so I think we are ready to land for this PR :)

Let me know if further comment on this

mylai-mtk

@kito-cheng It looks like the content of this PR is stable and ready to be merged, so I guess it the time to review it once again to reconfirm my knowledge and fine tune for wording, garmmar, etc. I've found quite a few typing mistakes/inappropriates in the process, but the content is good. Thanks for the effort!

mylai-mtk · 2025-02-25T01:59:32Z

riscv-elf.adoc

@@ -643,15 +643,29 @@ The PLT (Procedure Linkage Table) exists to allow function calls between
 dynamically linked shared objects. Each dynamic object has its own
 GOT (Global Offset Table) and PLT (Procedure Linkage Table).

+RISC-V has defined several PLT styles, which used for different situation,


Typo: RISC-V defines several PLT styles, which are used in different situations.

mylai-mtk · 2025-02-25T02:02:49Z

riscv-elf.adoc

@@ -643,15 +643,29 @@ The PLT (Procedure Linkage Table) exists to allow function calls between
 dynamically linked shared objects. Each dynamic object has its own
 GOT (Global Offset Table) and PLT (Procedure Linkage Table).

+RISC-V has defined several PLT styles, which used for different situation,
+the default PLT sytle should be used if the program is not met the condition for


Typo: The default PLT style should be used if the program does not meet the ~~condition~~ conditions for

mylai-mtk · 2025-02-25T02:03:25Z

riscv-elf.adoc

@@ -643,15 +643,29 @@ The PLT (Procedure Linkage Table) exists to allow function calls between
 dynamically linked shared objects. Each dynamic object has its own
 GOT (Global Offset Table) and PLT (Procedure Linkage Table).

+RISC-V has defined several PLT styles, which used for different situation,
+the default PLT sytle should be used if the program is not met the condition for
+using all other PLT sytle.


Typo: using all other PLT styles.

mylai-mtk · 2025-02-25T02:07:42Z

riscv-elf.adoc

-function pointer from the GOT. On the first call to a function, the
-entry redirects to the first PLT entry which calls `_dl_runtime_resolve`
-and fills in the GOT entry for subsequent calls to the function:
+And occupies three 16 byte entries for the simple landing pad PLT style:


Type: And occupies three 16 byte entries for the unlabeled landing pad PLT style:

mylai-mtk · 2025-02-25T02:35:56Z

riscv-elf.adoc

+1:  lpad 0
+    auipc  t2, %pcrel_hi(.got.plt)


Typo:

lpad 0 1: auipc t2, %pcrel_hi(.got.plt)

mylai-mtk · 2025-02-25T03:17:50Z

riscv-elf.adoc

@@ -678,6 +710,15 @@ and fills in the GOT entry for subsequent calls to the function:
    nop
 ----

+The code sequences of the PLT entry for the the simple landing pad PLT style:


Typo: The code sequences of the PLT entry for the ~~the~~ unlabeled landing pad PLT style:

mylai-mtk · 2025-02-25T03:25:20Z

riscv-elf.adoc

+`GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_UNLABELED` This bit indicate that all
+executable sections are built to be compatible with the landing pad mechanism
+provided by the `Zicfilp` extension. An executable or shared library with this
+bit set is required to generate PLTs with the landing pad (`lpad`) instruction,
+and all label are set to `0`.


Rephrase to avoid confusing with the to-be-added func-sig scheme-specifics:

This bit indicates that all executable sections are built to be compatible with the landing pad mechanism
provided by the Zicfilp extension in the unlabeled scheme: Executables and shared libraries with this bit set are required to generate PLTs in the unlabeled landing pad PLT style, and all of the labels of lpad instructions are set to 0, i.e. unlabeled.

mylai-mtk · 2025-02-25T03:25:37Z

riscv-elf.adoc

+bit set is required to generate PLTs with the landing pad (`lpad`) instruction,
+and all label are set to `0`.
+
+`GNU_PROPERTY_RISCV_FEATURE_1_CFI_SS`: This bit indicate that all executable


Typo: GNU_PROPERTY_RISCV_FEATURE_1_CFI_SS: This bit indicates that all executable

mylai-mtk · 2025-02-25T03:28:49Z

riscv-elf.adoc

+the `Zicfiss` extension. Loading an executable or shared library with this bit
+set requires the execution environment to provide either the `Zicfiss` extension
+or the `Zimop` extension. When the executable or shared library is compiled with
+compressed instructions then loading an executable with this bit set requires


Rephrase: compressed instructions then loading ~~an executable~~ it with this bit set requires

mylai-mtk · 2025-02-25T03:29:27Z

riscv-elf.adoc

+set requires the execution environment to provide either the `Zicfiss` extension
+or the `Zimop` extension. When the executable or shared library is compiled with
+compressed instructions then loading an executable with this bit set requires
+the execution environment to provide the `Zicfiss` extension or to provide both


Rephrase: the execution environment to provide the Zicfiss extension or ~~to provide~~ both

kito-cheng requested review from asb, rui314, MaskRay, jrtc27, aswaterman and Nelson1225 January 4, 2024 08:27

ved-rivos reviewed Jan 4, 2024

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kito-cheng changed the title ~~Add property for CFI extension~~ Add program property for CFI extension Jan 11, 2024

kito-cheng mentioned this pull request Feb 2, 2024

Allocate e_flags for landing pad and shadow stack #395

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topperc mentioned this pull request Feb 5, 2024

[RISCV] Add Zicfiss support to the shadow call stack implementation. llvm/llvm-project#68075

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SuHo-llrr mentioned this pull request Feb 15, 2024

[RISCV] Support .note.gnu.property for enable Zicfiss and Zicfilp extension llvm/llvm-project#77414

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kito-cheng mentioned this pull request Feb 26, 2024

Add program property #428

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kito-cheng changed the base branch from master to prog-prop February 26, 2024 09:56

kito-cheng force-pushed the cfi-prop branch from 1e785fa to 6b5ef1b Compare February 26, 2024 09:57

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kito-cheng force-pushed the cfi-prop branch from 59ceceb to 6016e63 Compare February 26, 2024 12:43

kito-cheng changed the title ~~Add program property for CFI extension~~ Add program property and PLT for CFI extension Feb 26, 2024

kito-cheng force-pushed the cfi-prop branch from c992d06 to be1260b Compare July 16, 2024 14:02

kito-cheng force-pushed the prog-prop branch from 31ba3a1 to 9ee857d Compare July 16, 2024 14:03

kito-cheng added 7 commits July 17, 2024 15:45

Add program property for CFI extension

e033d40

Define two bit for landing pad and shadow stack, and we plan to defined third bit `GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_COMPLEX` for complex labeling scheme.

Tweak table layout

42b788a

Update simple labeling scheme to use 0

e329ce7

Add simple landing pad PLT

281d12e

Drop DT_RISCV_SIMPLE_LP_PLT

21f36c4

Add one more nop for alignment

a56680d

Minor revision

a2ce820

Changes: - Rename `GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_SIMPLE` to `GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_UNLABELED` - Fix wrong offset in the first PLT stubs for the simple landing pad PLT.

kito-cheng force-pushed the cfi-prop branch from be1260b to a2ce820 Compare July 17, 2024 08:02

Base automatically changed from prog-prop to master August 2, 2024 06:48

kito-cheng mentioned this pull request Sep 5, 2024

Add options for enable code gen with CFI `-fcf-protection=[full|branc… riscv-non-isa/riscv-toolchain-conventions#54

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jerryzj mentioned this pull request Dec 17, 2024

[RISCV] Add GNU note property and CFI support eliben/pyelftools#587

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mylai-mtk mentioned this pull request Feb 24, 2025

[RISCV] Emit .note.gnu.property section when Zicfiss-based shadow stack is enabled llvm/llvm-project#127036

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mylai-mtk reviewed Feb 25, 2025

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mylai-mtk mentioned this pull request Feb 27, 2025

[LLD][ELF][RISCV] Handle .note.gnu.property sections for Zicfilp/Zicfiss features llvm/llvm-project#127193

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Add program property and PLT for CFI extension #417

Add program property and PLT for CFI extension #417

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