[llvm-branch-commits] [llvm] [BOLT] Gadget scanner: account for BRK when searching for auth oracles (PR #137975)
Anatoly Trosinenko via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Mon Jun 23 06:50:29 PDT 2025
https://github.com/atrosinenko updated https://github.com/llvm/llvm-project/pull/137975
>From 66ad4fa5219cca41bcd4c5fefc6415be4f45b361 Mon Sep 17 00:00:00 2001
From: Anatoly Trosinenko <atrosinenko at accesssoftek.com>
Date: Wed, 30 Apr 2025 16:08:10 +0300
Subject: [PATCH] [BOLT] Gadget scanner: account for BRK when searching for
auth oracles
An authenticated pointer can be explicitly checked by the compiler via a
sequence of instructions that executes BRK on failure. It is important
to recognize such BRK instruction as checking every register (as it is
expected to immediately trigger an abnormal program termination) to
prevent false positive reports about authentication oracles:
autia x2, x3
autia x0, x1
; neither x0 nor x2 are checked at this point
eor x16, x0, x0, lsl #1
tbz x16, #62, on_success ; marks x0 as checked
; end of BB: for x2 to be checked here, it must be checked in both
; successor basic blocks
on_failure:
brk 0xc470
on_success:
; x2 is checked
ldr x1, [x2] ; marks x2 as checked
---
bolt/include/bolt/Core/MCPlusBuilder.h | 14 ++++++
bolt/lib/Passes/PAuthGadgetScanner.cpp | 13 +++++-
.../Target/AArch64/AArch64MCPlusBuilder.cpp | 24 ++++++++--
.../AArch64/gs-pauth-address-checks.s | 44 +++++++++----------
.../AArch64/gs-pauth-authentication-oracles.s | 9 ++--
.../AArch64/gs-pauth-signing-oracles.s | 6 +--
6 files changed, 75 insertions(+), 35 deletions(-)
diff --git a/bolt/include/bolt/Core/MCPlusBuilder.h b/bolt/include/bolt/Core/MCPlusBuilder.h
index 804100db80793..c31c9984ed43e 100644
--- a/bolt/include/bolt/Core/MCPlusBuilder.h
+++ b/bolt/include/bolt/Core/MCPlusBuilder.h
@@ -707,6 +707,20 @@ class MCPlusBuilder {
return false;
}
+ /// Returns true if Inst is a trap instruction.
+ ///
+ /// Tests if Inst is an instruction that immediately causes an abnormal
+ /// program termination, for example when a security violation is detected
+ /// by a compiler-inserted check.
+ ///
+ /// @note An implementation of this method should likely return false for
+ /// calls to library functions like abort(), as it is possible that the
+ /// execution state is partially attacker-controlled at this point.
+ virtual bool isTrap(const MCInst &Inst) const {
+ llvm_unreachable("not implemented");
+ return false;
+ }
+
virtual bool isBreakpoint(const MCInst &Inst) const {
llvm_unreachable("not implemented");
return false;
diff --git a/bolt/lib/Passes/PAuthGadgetScanner.cpp b/bolt/lib/Passes/PAuthGadgetScanner.cpp
index 0a3948e2e278e..16fd24745bc53 100644
--- a/bolt/lib/Passes/PAuthGadgetScanner.cpp
+++ b/bolt/lib/Passes/PAuthGadgetScanner.cpp
@@ -1078,6 +1078,15 @@ class DstSafetyAnalysis {
dbgs() << ")\n";
});
+ // If this instruction terminates the program immediately, no
+ // authentication oracles are possible past this point.
+ if (BC.MIB->isTrap(Point)) {
+ LLVM_DEBUG({ traceInst(BC, "Trap instruction found", Point); });
+ DstState Next(NumRegs, RegsToTrackInstsFor.getNumTrackedRegisters());
+ Next.CannotEscapeUnchecked.set();
+ return Next;
+ }
+
// If this instruction is reachable by the analysis, a non-empty state will
// be propagated to it sooner or later. Until then, skip computeNext().
if (Cur.empty()) {
@@ -1185,8 +1194,8 @@ class DataflowDstSafetyAnalysis
//
// A basic block without any successors, on the other hand, can be
// pessimistically initialized to everything-is-unsafe: this will naturally
- // handle both return and tail call instructions and is harmless for
- // internal indirect branch instructions (such as computed gotos).
+ // handle return, trap and tail call instructions. At the same time, it is
+ // harmless for internal indirect branch instructions, like computed gotos.
if (BB.succ_empty())
return createUnsafeState();
diff --git a/bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp b/bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp
index eb1d9d8a19514..ac454a43e8a59 100644
--- a/bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp
+++ b/bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp
@@ -386,10 +386,9 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
// the list of successors of this basic block as appropriate.
// Any of the above code sequences assume the fall-through basic block
- // is a dead-end BRK instruction (any immediate operand is accepted).
+ // is a dead-end trap instruction.
const BinaryBasicBlock *BreakBB = BB.getFallthrough();
- if (!BreakBB || BreakBB->empty() ||
- BreakBB->front().getOpcode() != AArch64::BRK)
+ if (!BreakBB || BreakBB->empty() || !isTrap(BreakBB->front()))
return std::nullopt;
// Iterate over the instructions of BB in reverse order, matching opcodes
@@ -1751,6 +1750,25 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
Inst.addOperand(MCOperand::createImm(0));
}
+ bool isTrap(const MCInst &Inst) const override {
+ if (Inst.getOpcode() != AArch64::BRK)
+ return false;
+ // Only match the immediate values that are likely to indicate this BRK
+ // instruction is emitted to terminate the program immediately and not to
+ // be handled by a SIGTRAP handler, for example.
+ switch (Inst.getOperand(0).getImm()) {
+ case 0xc470:
+ case 0xc471:
+ case 0xc472:
+ case 0xc473:
+ // Explicit Pointer Authentication check failed, see
+ // AArch64AsmPrinter::emitPtrauthCheckAuthenticatedValue().
+ return true;
+ default:
+ return false;
+ }
+ }
+
bool isStorePair(const MCInst &Inst) const {
const unsigned opcode = Inst.getOpcode();
diff --git a/bolt/test/binary-analysis/AArch64/gs-pauth-address-checks.s b/bolt/test/binary-analysis/AArch64/gs-pauth-address-checks.s
index 3f982ddaf6e38..74f276197923f 100644
--- a/bolt/test/binary-analysis/AArch64/gs-pauth-address-checks.s
+++ b/bolt/test/binary-analysis/AArch64/gs-pauth-address-checks.s
@@ -31,7 +31,7 @@ resign_xpaci_good:
xpaci x16
cmp x0, x16
b.eq 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x0, x2
ret
@@ -46,7 +46,7 @@ resign_xpacd_good:
xpacd x16
cmp x0, x16
b.eq 1f
- brk 0x1234
+ brk 0xc473
1:
pacda x0, x2
ret
@@ -117,7 +117,7 @@ resign_xpaci_unrelated_auth_and_check:
xpaci x16
cmp x0, x16
b.eq 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x10, x2
ret
@@ -139,7 +139,7 @@ resign_xpaci_wrong_pattern_1:
xpaci x16
cmp x0, x16
b.eq 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x0, x2
ret
@@ -157,7 +157,7 @@ resign_xpaci_wrong_pattern_2:
xpaci x0 // x0 instead of x16
cmp x0, x16
b.eq 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x0, x2
ret
@@ -174,7 +174,7 @@ resign_xpaci_wrong_pattern_3:
xpaci x16
cmp x16, x16 // x16 instead of x0
b.eq 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x0, x2
ret
@@ -191,7 +191,7 @@ resign_xpaci_wrong_pattern_4:
xpaci x16
cmp x0, x0 // x0 instead of x16
b.eq 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x0, x2
ret
@@ -208,7 +208,7 @@ resign_xpaci_wrong_pattern_5:
mov x16, x16 // replace xpaci with a no-op instruction
cmp x0, x16
b.eq 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x0, x2
ret
@@ -228,7 +228,7 @@ resign_xpaclri_good:
xpaclri
cmp x30, x16
b.eq 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x30, x2
@@ -246,7 +246,7 @@ xpaclri_check_keeps_lr_safe:
xpaclri // clobbers LR
cmp x30, x16
b.eq 1f
- brk 0x1234 // marks LR as trusted and safe-to-dereference
+ brk 0xc471 // marks LR as trusted and safe-to-dereference
1:
ret // not reporting non-protected return
.size xpaclri_check_keeps_lr_safe, .-xpaclri_check_keeps_lr_safe
@@ -265,7 +265,7 @@ xpaclri_check_requires_safe_lr:
xpaclri
cmp x30, x16
b.eq 1f
- brk 0x1234
+ brk 0xc471
1:
ret
.size xpaclri_check_requires_safe_lr, .-xpaclri_check_requires_safe_lr
@@ -283,7 +283,7 @@ resign_xpaclri_wrong_reg:
xpaclri // ... but xpaclri still operates on x30
cmp x20, x16
b.eq 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x20, x2
@@ -303,7 +303,7 @@ resign_checked_not_authenticated:
xpaci x16
cmp x0, x16
b.eq 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x0, x2
ret
@@ -323,7 +323,7 @@ resign_checked_before_authenticated:
xpaci x16
cmp x0, x16
b.eq 1f
- brk 0x1234
+ brk 0xc471
1:
autib x0, x1
pacia x0, x2
@@ -339,7 +339,7 @@ resign_high_bits_tbz_good:
autib x0, x1
eor x16, x0, x0, lsl #1
tbz x16, #62, 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x0, x2
ret
@@ -378,7 +378,7 @@ resign_high_bits_tbz_wrong_bit:
autib x0, x1
eor x16, x0, x0, lsl #1
tbz x16, #63, 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x0, x2
ret
@@ -393,7 +393,7 @@ resign_high_bits_tbz_wrong_shift_amount:
autib x0, x1
eor x16, x0, x0, lsl #2
tbz x16, #62, 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x0, x2
ret
@@ -408,7 +408,7 @@ resign_high_bits_tbz_wrong_shift_type:
autib x0, x1
eor x16, x0, x0, lsr #1
tbz x16, #62, 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x0, x2
ret
@@ -423,7 +423,7 @@ resign_high_bits_tbz_wrong_pattern_1:
autib x0, x1
eor x16, x0, x0, lsl #1
tbz x17, #62, 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x0, x2
ret
@@ -438,7 +438,7 @@ resign_high_bits_tbz_wrong_pattern_2:
autib x0, x1
eor x16, x10, x0, lsl #1
tbz x16, #62, 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x0, x2
ret
@@ -453,7 +453,7 @@ resign_high_bits_tbz_wrong_pattern_3:
autib x0, x1
eor x16, x0, x10, lsl #1
tbz x16, #62, 1f
- brk 0x1234
+ brk 0xc471
1:
pacia x0, x2
ret
@@ -648,7 +648,7 @@ many_checked_regs:
xpacd x16 // ...
cmp x2, x16 // ...
b.eq 2f // end of basic block
- brk 0x1234
+ brk 0xc473
2:
pacdza x0
pacdza x1
diff --git a/bolt/test/binary-analysis/AArch64/gs-pauth-authentication-oracles.s b/bolt/test/binary-analysis/AArch64/gs-pauth-authentication-oracles.s
index c314bc7cfe5a3..f44ba21b9d484 100644
--- a/bolt/test/binary-analysis/AArch64/gs-pauth-authentication-oracles.s
+++ b/bolt/test/binary-analysis/AArch64/gs-pauth-authentication-oracles.s
@@ -79,7 +79,7 @@ good_explicit_check:
autia x0, x1
eor x16, x0, x0, lsl #1
tbz x16, #62, 1f
- brk 0x1234
+ brk 0xc470
1:
ret
.size good_explicit_check, .-good_explicit_check
@@ -373,7 +373,7 @@ good_explicit_check_multi_bb:
1:
eor x16, x0, x0, lsl #1
tbz x16, #62, 2f
- brk 0x1234
+ brk 0xc470
2:
cbz x1, 3f
nop
@@ -685,8 +685,7 @@ good_address_arith_nocfg:
.globl good_explicit_check_unrelated_reg
.type good_explicit_check_unrelated_reg, at function
good_explicit_check_unrelated_reg:
-// CHECK-LABEL: GS-PAUTH: authentication oracle found in function good_explicit_check_unrelated_reg, basic block {{[^,]+}}, at address
- // FIXME: The below instruction is not an authentication oracle
+// CHECK-NOT: good_explicit_check_unrelated_reg
autia x2, x3 // One of possible execution paths after this instruction
// ends at BRK below, thus BRK used as a trap instruction
// should formally "check everything" not to introduce
@@ -694,7 +693,7 @@ good_explicit_check_unrelated_reg:
autia x0, x1
eor x16, x0, x0, lsl #1
tbz x16, #62, 1f
- brk 0x1234
+ brk 0xc470
1:
ldr x4, [x2] // Right before this instruction X2 is checked - this
// should be propagated to the basic block ending with
diff --git a/bolt/test/binary-analysis/AArch64/gs-pauth-signing-oracles.s b/bolt/test/binary-analysis/AArch64/gs-pauth-signing-oracles.s
index 3a4d383ec5bc6..4d4bb7b0fb251 100644
--- a/bolt/test/binary-analysis/AArch64/gs-pauth-signing-oracles.s
+++ b/bolt/test/binary-analysis/AArch64/gs-pauth-signing-oracles.s
@@ -57,7 +57,7 @@ good_sign_auted_checked_brk:
autda x0, x2
eor x16, x0, x0, lsl #1
tbz x16, #62, 1f
- brk 0x1234
+ brk 0xc472
1:
pacda x0, x1
ret
@@ -351,7 +351,7 @@ good_sign_auted_checked_brk_multi_bb:
1:
eor x16, x0, x0, lsl #1
tbz x16, #62, 2f
- brk 0x1234
+ brk 0xc472
2:
cbz x4, 3f
nop
@@ -705,7 +705,7 @@ good_resign_with_increment_brk:
add x0, x0, #8
eor x16, x0, x0, lsl #1
tbz x16, #62, 1f
- brk 0x1234
+ brk 0xc472
1:
mov x2, x0
pacda x2, x1
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