[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
Tue May 20 03:03:43 PDT 2025
https://github.com/atrosinenko updated https://github.com/llvm/llvm-project/pull/137975
>From 47a6ece20ffb8cedf3c86650886e73d8bdc463d7 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 6d3aa4f5f0feb..87de6754017db 100644
--- a/bolt/include/bolt/Core/MCPlusBuilder.h
+++ b/bolt/include/bolt/Core/MCPlusBuilder.h
@@ -706,6 +706,20 @@ 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 dfb71575b2b39..835ee26aaf08a 100644
--- a/bolt/lib/Passes/PAuthGadgetScanner.cpp
+++ b/bolt/lib/Passes/PAuthGadgetScanner.cpp
@@ -1028,6 +1028,15 @@ 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()) {
@@ -1133,8 +1142,8 @@ 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 f3c29e6ee43b9..4d11c5b206eab 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
@@ -1745,6 +1744,25 @@ 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 b4a69e855a046..b199c3056ba5b 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
@@ -301,7 +301,7 @@ 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
@@ -613,8 +613,7 @@ 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
@@ -622,7 +621,7 @@ 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 1ead398959fd6..94b2c55f3bfa6 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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