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[PAC][ThinLTO] Fix auth key for GOT entries of function symbols (#131467)

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Symtab is first filled with the data from the bitcode file, and all
undefined symbols except TLS ones are `STT_NOTYPE`. Since auth key for a
signed GOT entry depends on the symbol type being `STT_FUNC` or not, we
need to update the symtab after the bitcode is compiled to an ELF object
and update symbol types for function symbols. This patch implements the
described behavior.
This commit is contained in:
Daniil Kovalev 2025-04-19 17:40:50 +03:00 committed by GitHub
parent fc55ad4ceb
commit 8fdebff69d
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2 changed files with 78 additions and 0 deletions
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12
lld/ELF/Driver.cpp
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@ -2638,6 +2638,18 @@ void LinkerDriver::compileBitcodeFiles(bool skipLinkedOutput) {
auto *obj = cast<ObjFile<ELFT>>(file.get());
obj->parse(/*ignoreComdats=*/true);
// This is only needed for AArch64 PAuth to set correct key in AUTH GOT
// entry based on symbol type (STT_FUNC or not).
// TODO: check if PAuth is actually used.
if (ctx.arg.emachine == EM_AARCH64) {
for (typename ELFT::Sym elfSym : obj->template getGlobalELFSyms<ELFT>()) {
StringRef elfSymName = check(elfSym.getName(obj->getStringTable()));
if (Symbol *sym = ctx.symtab->find(elfSymName))
if (sym->type == STT_NOTYPE)
sym->type = elfSym.getType();
}
}
// For defined symbols in non-relocatable output,
// compute isExported and parse '@'.
if (!ctx.arg.relocatable)

66
lld/test/ELF/lto/aarch64-pac-got-func.ll Normal file
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@ -0,0 +1,66 @@
; REQUIRES: aarch64
; RUN: llvm-as %s -o %t.o
; RUN: ld.lld %t.o -shared -o %t
; RUN: llvm-readelf -r -x.got %t | FileCheck %s
; CHECK: Relocation section '.rela.dyn' at offset 0x3d0 contains 8 entries:
; CHECK-NEXT: Offset Info Type Symbol's Value Symbol's Name + Addend
; CHECK-NEXT: 00000000000206a0 0000000100000412 R_AARCH64_AUTH_GLOB_DAT 0000000000000000 func_undef + 0
; CHECK-NEXT: 00000000000206a8 0000000200000412 R_AARCH64_AUTH_GLOB_DAT 0000000000000000 g1 + 0
; CHECK-NEXT: 00000000000206b0 0000000300000412 R_AARCH64_AUTH_GLOB_DAT 0000000000000000 g2 + 0
; CHECK-NEXT: 00000000000206b8 0000000400000412 R_AARCH64_AUTH_GLOB_DAT 0000000000000000 g3 + 0
; CHECK-NEXT: 00000000000206c0 0000000500000412 R_AARCH64_AUTH_GLOB_DAT 0000000000000000 g4 + 0
; CHECK-NEXT: 00000000000206c8 0000000600000412 R_AARCH64_AUTH_GLOB_DAT 0000000000000000 var_undef + 0
; CHECK-NEXT: 0000000000020690 0000000700000412 R_AARCH64_AUTH_GLOB_DAT 0000000000010490 func + 0
; CHECK-NEXT: 0000000000020698 0000000a00000412 R_AARCH64_AUTH_GLOB_DAT 00000000000306d0 var + 0
; CHECK: Hex dump of section '.got':
; CHECK-NEXT: 0x00020690 00000000 00000080 00000000 000000a0
;; ^^ func: 0b10000000 bit 63 address diversity = true, bits 61..60 key = IA
;; ^^ var: 0b10100000 bit 63 address diversity = true, bits 61..60 key = DA
; CHECK-NEXT: 0x000206a0 00000000 00000080 00000000 000000a0
;; ^^ func_undef: 0b10000000 bit 63 address diversity = true, bits 61..60 key = IA
;; ^^ g1: 0b10100000 bit 63 address diversity = true, bits 61..60 key = DA
; CHECK-NEXT: 0x000206b0 00000000 000000a0 00000000 000000a0
;; ^^ g2: 0b10100000 bit 63 address diversity = true, bits 61..60 key = DA
;; ^^ g3: 0b10100000 bit 63 address diversity = true, bits 61..60 key = DA
; CHECK-NEXT: 0x000206c0 00000000 000000a0 00000000 000000a0
;; ^^ g4: 0b10100000 bit 63 address diversity = true, bits 61..60 key = DA
;; ^^ var_undef: 0b10100000 bit 63 address diversity = true, bits 61..60 key = DA
target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
target triple = "aarch64-unknown-linux-gnu"
@g1 = external global ptr
@g2 = external global ptr
@g3 = external global ptr
@g4 = external global ptr
define void @func() {
entry:
ret void
}
declare void @func_undef()
@var = global i32 42
@var_undef = external global i32
define void @bar() #0 {
entry:
store ptr ptrauth (ptr @func, i32 0), ptr @g1
store ptr ptrauth (ptr @func_undef, i32 0), ptr @g2
store ptr ptrauth (ptr @var, i32 0), ptr @g3
store ptr ptrauth (ptr @var_undef, i32 0), ptr @g4
ret void
}
define void @_start() {
entry:
ret void
}
attributes #0 = {"target-features"="+pauth"}
!llvm.module.flags = !{!0}
!0 = !{i32 8, !"ptrauth-elf-got", i32 1}