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Set branch protection function attributes

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Since LLVM 19, it is necessary to set not only module flags, but
also function attributes for branch protection on aarch64. See
e15d67cfc2
for the relevant LLVM change.
This commit is contained in:
Nikita Popov 2024-07-24 16:47:56 +02:00
parent d24930ceb4
commit ea7625f426
3 changed files with 83 additions and 3 deletions
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31
compiler/rustc_codegen_llvm/src/attributes.rs
View File

@ -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;
@ -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 {
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)

45
tests/codegen/branch-protection-old-llvm.rs Normal file
View File

@ -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
tests/codegen/branch-protection.rs
View File

@ -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)]
@ -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