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Set branch protection function attributes #128141

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merged 1 commit into from
Jul 30, 2024
Merged

Set branch protection function attributes #128141

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31 changes: 28 additions & 3 deletions compiler/rustc_codegen_llvm/src/attributes.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@ use rustc_codegen_ssa::traits::*;
use rustc_hir::def_id::DefId;
use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, PatchableFunctionEntry};
use rustc_middle::ty::{self, TyCtxt};
use rustc_session::config::{FunctionReturn, OptLevel};
use rustc_session::config::{BranchProtection, FunctionReturn, OptLevel, PAuthKey, PacRet};
use rustc_span::symbol::sym;
use rustc_target::spec::{FramePointer, SanitizerSet, StackProbeType, StackProtector};
use smallvec::SmallVec;
Expand Down Expand Up @@ -407,8 +407,33 @@ pub fn from_fn_attrs<'ll, 'tcx>(
// And it is a module-level attribute, so the alternative is pulling naked functions into new LLVM modules.
// Otherwise LLVM's "naked" functions come with endbr prefixes per https://github.com/rust-lang/rust/issues/98768
to_add.push(AttributeKind::NoCfCheck.create_attr(cx.llcx));
// Need this for AArch64.
to_add.push(llvm::CreateAttrStringValue(cx.llcx, "branch-target-enforcement", "false"));
if llvm_util::get_version() < (19, 0, 0) {
// Prior to LLVM 19, branch-target-enforcement was disabled by setting the attribute to
// the string "false". Now it is disabled by absence of the attribute.
to_add.push(llvm::CreateAttrStringValue(cx.llcx, "branch-target-enforcement", "false"));
}
} else if llvm_util::get_version() >= (19, 0, 0) {
// For non-naked functions, set branch protection attributes on aarch64.
if let Some(BranchProtection { bti, pac_ret }) =
cx.sess().opts.unstable_opts.branch_protection
{
assert!(cx.sess().target.arch == "aarch64");
if bti {
to_add.push(llvm::CreateAttrString(cx.llcx, "branch-target-enforcement"));
}
if let Some(PacRet { leaf, key }) = pac_ret {
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Should we use let pac_opts = pac_ret.unwrap_or(PacRet { leaf: false, key: PAuthKey::A });? See

rust/compiler/rustc_codegen_llvm/src/context.rs

Line 292 in a5ee5cb

let pac_opts = pac_ret.unwrap_or(PacRet { leaf: false, key: PAuthKey::A });
.

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I don't think so. Note that, while that code makes it look like non-leaf a-key is the default, this is not actually the case, as sign-return-address is still set to false in the None case and the overall functionality is disabled. (I think the reason why it's always setting all module flags is to get correct module flag merging behavior during LTO, but not entirely sure on that.)

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For reference, this matches the corresponding clang logic for the function attrs: https://github.com/llvm/llvm-project/blob/5bd3aef5e285cce793e3fc6b21299ac9d650a947/clang/lib/CodeGen/TargetInfo.cpp#L219-L222

to_add.push(llvm::CreateAttrStringValue(
cx.llcx,
"sign-return-address",
if leaf { "all" } else { "non-leaf" },
));
to_add.push(llvm::CreateAttrStringValue(
cx.llcx,
"sign-return-address-key",
if key == PAuthKey::A { "a_key" } else { "b_key" },
));
}
}
}
if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::ALLOCATOR)
|| codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::ALLOCATOR_ZEROED)
Expand Down
45 changes: 45 additions & 0 deletions tests/codegen/branch-protection-old-llvm.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,45 @@
// Test that the correct module flags are emitted with different branch protection flags.

//@ revisions: BTI PACRET LEAF BKEY NONE
//@ needs-llvm-components: aarch64
//@ [BTI] compile-flags: -Z branch-protection=bti
//@ [PACRET] compile-flags: -Z branch-protection=pac-ret
//@ [LEAF] compile-flags: -Z branch-protection=pac-ret,leaf
//@ [BKEY] compile-flags: -Z branch-protection=pac-ret,b-key
//@ compile-flags: --target aarch64-unknown-linux-gnu
//@ ignore-llvm-version: 19 - 99

#![crate_type = "lib"]
#![feature(no_core, lang_items)]
#![no_core]

#[lang = "sized"]
trait Sized {}

// A basic test function.
pub fn test() {}

// BTI: !"branch-target-enforcement", i32 1
// BTI: !"sign-return-address", i32 0
// BTI: !"sign-return-address-all", i32 0
// BTI: !"sign-return-address-with-bkey", i32 0

// PACRET: !"branch-target-enforcement", i32 0
// PACRET: !"sign-return-address", i32 1
// PACRET: !"sign-return-address-all", i32 0
// PACRET: !"sign-return-address-with-bkey", i32 0

// LEAF: !"branch-target-enforcement", i32 0
// LEAF: !"sign-return-address", i32 1
// LEAF: !"sign-return-address-all", i32 1
// LEAF: !"sign-return-address-with-bkey", i32 0

// BKEY: !"branch-target-enforcement", i32 0
// BKEY: !"sign-return-address", i32 1
// BKEY: !"sign-return-address-all", i32 0
// BKEY: !"sign-return-address-with-bkey", i32 1

// NONE-NOT: branch-target-enforcement
// NONE-NOT: sign-return-address
// NONE-NOT: sign-return-address-all
// NONE-NOT: sign-return-address-with-bkey
10 changes: 10 additions & 0 deletions tests/codegen/branch-protection.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@
//@ [LEAF] compile-flags: -Z branch-protection=pac-ret,leaf
//@ [BKEY] compile-flags: -Z branch-protection=pac-ret,b-key
//@ compile-flags: --target aarch64-unknown-linux-gnu
//@ min-llvm-version: 19

#![crate_type = "lib"]
#![feature(no_core, lang_items)]
Expand All @@ -16,23 +17,32 @@
trait Sized {}

// A basic test function.
// CHECK: @test(){{.*}} [[ATTR:#[0-9]+]] {
#[no_mangle]
pub fn test() {}

// BTI: attributes [[ATTR]] = {{.*}} "branch-target-enforcement"
// BTI: !"branch-target-enforcement", i32 1
// BTI: !"sign-return-address", i32 0
// BTI: !"sign-return-address-all", i32 0
// BTI: !"sign-return-address-with-bkey", i32 0

// PACRET: attributes [[ATTR]] = {{.*}} "sign-return-address"="non-leaf"
// PACRET-SAME: "sign-return-address-key"="a_key"
// PACRET: !"branch-target-enforcement", i32 0
// PACRET: !"sign-return-address", i32 1
// PACRET: !"sign-return-address-all", i32 0
// PACRET: !"sign-return-address-with-bkey", i32 0

// LEAF: attributes [[ATTR]] = {{.*}} "sign-return-address"="all"
// LEAF-SAME: "sign-return-address-key"="a_key"
// LEAF: !"branch-target-enforcement", i32 0
// LEAF: !"sign-return-address", i32 1
// LEAF: !"sign-return-address-all", i32 1
// LEAF: !"sign-return-address-with-bkey", i32 0

// BKEY: attributes [[ATTR]] = {{.*}} "sign-return-address"="non-leaf"
// BKEY-SAME: "sign-return-address-key"="b_key"
// BKEY: !"branch-target-enforcement", i32 0
// BKEY: !"sign-return-address", i32 1
// BKEY: !"sign-return-address-all", i32 0
Expand Down
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