[HWASan] Save + print registers when tag mismatch occurs in AArch64.

Summary:
This change change the instrumentation to allow users to view the registers at the point at which tag mismatch occured. Most of the heavy lifting is done in the runtime library, where we save the registers to the stack and emit unwind information. This allows us to reduce the overhead, as very little additional work needs to be done in each __hwasan_check instance.

In this implementation, the fast path of __hwasan_check is unmodified. There are an additional 4 instructions (16B) emitted in the slow path in every __hwasan_check instance. This may increase binary size somewhat, but as most of the work is done in the runtime library, it's manageable.

The failure trace now contains a list of registers at the point of which the failure occured, in a format similar to that of Android's tombstones. It currently has the following format:

Registers where the failure occurred (pc 0x0055555561b4):
    x0  0000000000000014  x1  0000007ffffff6c0  x2  1100007ffffff6d0  x3  12000056ffffe025
    x4  0000007fff800000  x5  0000000000000014  x6  0000007fff800000  x7  0000000000000001
    x8  12000056ffffe020  x9  0200007700000000  x10 0200007700000000  x11 0000000000000000
    x12 0000007fffffdde0  x13 0000000000000000  x14 02b65b01f7a97490  x15 0000000000000000
    x16 0000007fb77376b8  x17 0000000000000012  x18 0000007fb7ed6000  x19 0000005555556078
    x20 0000007ffffff768  x21 0000007ffffff778  x22 0000000000000001  x23 0000000000000000
    x24 0000000000000000  x25 0000000000000000  x26 0000000000000000  x27 0000000000000000
    x28 0000000000000000  x29 0000007ffffff6f0  x30 00000055555561b4

... and prints after the dump of memory tags around the buggy address.

Every register is saved exactly as it was at the point where the tag mismatch occurs, with the exception of x16/x17. These registers are used in the tag mismatch calculation as scratch registers during __hwasan_check, and cannot be saved without affecting the fast path. As these registers are designated as scratch registers for linking, there should be no important information in them that could aid in debugging.

Reviewers: pcc, eugenis

Reviewed By: pcc, eugenis

Subscribers: srhines, kubamracek, mgorny, javed.absar, krytarowski, kristof.beyls, hiraditya, jdoerfert, llvm-commits, #sanitizers

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D58857

Change-Id: I7efa8a42509e9e00ebdb5b6a0ddde8c6dc08ae7e
git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@355738 91177308-0d34-0410-b5e6-96231b3b80d8

7 files changed, 201 insertions, 8 deletions

diff --git a/lib/hwasan/CMakeLists.txt b/lib/hwasan/CMakeLists.txt
index a01c40710..e1704d1be 100644
--- a/lib/hwasan/CMakeLists.txt
+++ b/lib/hwasan/CMakeLists.txt
@@ -11,6 +11,7 @@ set(HWASAN_RTL_SOURCES
   hwasan_memintrinsics.cc
   hwasan_poisoning.cc
   hwasan_report.cc
+  hwasan_tag_mismatch_aarch64.S
   hwasan_thread.cc
   hwasan_thread_list.cc
   )
diff --git a/lib/hwasan/hwasan_interface_internal.h b/lib/hwasan/hwasan_interface_internal.h
index 315b0daef..3e5ac90be 100644
--- a/lib/hwasan/hwasan_interface_internal.h
+++ b/lib/hwasan/hwasan_interface_internal.h
@@ -100,6 +100,9 @@ SANITIZER_INTERFACE_ATTRIBUTE
 uptr __hwasan_tag_pointer(uptr p, u8 tag);
 
 SANITIZER_INTERFACE_ATTRIBUTE
+void __hwasan_tag_mismatch(uptr addr, u8 ts);
+
+SANITIZER_INTERFACE_ATTRIBUTE
 u8 __hwasan_generate_tag();
 
 // Returns the offset of the first tag mismatch or -1 if the whole range is
diff --git a/lib/hwasan/hwasan_linux.cc b/lib/hwasan/hwasan_linux.cc
index c922c1110..03f27c60b 100644
--- a/lib/hwasan/hwasan_linux.cc
+++ b/lib/hwasan/hwasan_linux.cc
@@ -374,15 +374,26 @@ static AccessInfo GetAccessInfo(siginfo_t *info, ucontext_t *uc) {
 }
 
 static void HandleTagMismatch(AccessInfo ai, uptr pc, uptr frame,
-                              ucontext_t *uc) {
+                              ucontext_t *uc, uptr *registers_frame = nullptr) {
   InternalMmapVector<BufferedStackTrace> stack_buffer(1);
   BufferedStackTrace *stack = stack_buffer.data();
   stack->Reset();
   GetStackTrace(stack, kStackTraceMax, pc, frame, uc,
                 common_flags()->fast_unwind_on_fatal);
 
+  // The second stack frame contains the failure __hwasan_check function, as
+  // we have a stack frame for the registers saved in __hwasan_tag_mismatch that
+  // we wish to ignore. This (currently) only occurs on AArch64, as x64
+  // implementations use SIGTRAP to implement the failure, and thus do not go
+  // through the stack saver.
+  if (registers_frame && stack->trace && stack->size > 0) {
+    stack->trace++;
+    stack->size--;
+  }
+
   bool fatal = flags()->halt_on_error || !ai.recover;
-  ReportTagMismatch(stack, ai.addr, ai.size, ai.is_store, fatal);
+  ReportTagMismatch(stack, ai.addr, ai.size, ai.is_store, fatal,
+                    registers_frame);
 }
 
 static bool HwasanOnSIGTRAP(int signo, siginfo_t *info, ucontext_t *uc) {
@@ -402,8 +413,10 @@ static bool HwasanOnSIGTRAP(int signo, siginfo_t *info, ucontext_t *uc) {
   return true;
 }
 
-extern "C" SANITIZER_INTERFACE_ATTRIBUTE void __hwasan_tag_mismatch(
-    uptr addr, uptr access_info) {
+// Entry point stub for interoperability between __hwasan_tag_mismatch (ASM) and
+// the rest of the mismatch handling code (C++).
+extern "C" void __hwasan_tag_mismatch_stub(uptr addr, uptr access_info,
+                                           uptr *registers_frame) {
   AccessInfo ai;
   ai.is_store = access_info & 0x10;
   ai.recover = false;
@@ -411,7 +424,7 @@ extern "C" SANITIZER_INTERFACE_ATTRIBUTE void __hwasan_tag_mismatch(
   ai.size = 1 << (access_info & 0xf);
 
   HandleTagMismatch(ai, (uptr)__builtin_return_address(0),
-                    (uptr)__builtin_frame_address(0), nullptr);
+                    (uptr)__builtin_frame_address(0), nullptr, registers_frame);
   __builtin_unreachable();
 }
 
diff --git a/lib/hwasan/hwasan_report.cc b/lib/hwasan/hwasan_report.cc
index 762171362..57c9b182b 100644
--- a/lib/hwasan/hwasan_report.cc
+++ b/lib/hwasan/hwasan_report.cc
@@ -14,6 +14,7 @@
 #include "hwasan.h"
 #include "hwasan_allocator.h"
 #include "hwasan_mapping.h"
+#include "hwasan_report.h"
 #include "hwasan_thread.h"
 #include "hwasan_thread_list.h"
 #include "sanitizer_common/sanitizer_allocator_internal.h"
@@ -389,7 +390,7 @@ void ReportTailOverwritten(StackTrace *stack, uptr tagged_addr, uptr orig_size,
 }
 
 void ReportTagMismatch(StackTrace *stack, uptr tagged_addr, uptr access_size,
-                       bool is_store, bool fatal) {
+                       bool is_store, bool fatal, uptr *registers_frame) {
   ScopedReport R(fatal);
   SavedStackAllocations current_stack_allocations(
       GetCurrentThread()->stack_allocations());
@@ -430,7 +431,31 @@ void ReportTagMismatch(StackTrace *stack, uptr tagged_addr, uptr access_size,
 
   PrintTagsAroundAddr(tag_ptr);
 
+  if (registers_frame)
+    ReportRegisters(registers_frame, pc);
+
   ReportErrorSummary(bug_type, stack);
 }
 
+// See the frame breakdown defined in __hwasan_tag_mismatch (from
+// hwasan_tag_mismatch_aarch64.S).
+static const char *kDoubleSpace = "  ";
+static const char *kSingleSpace = " ";
+void ReportRegisters(uptr *frame, uptr pc) {
+  Printf("Registers where the failure occurred (pc %p):", pc);
+
+  for (unsigned i = 0; i <= 30; i++) {
+    if (i % 4 == 0)
+      Printf("\n  ");
+
+    // Note - manually inserting a double or single space here based on the
+    // number of digits in the register name, as our sanitizer Printf does not
+    // support padding where the content is left aligned (i.e. the format
+    // specifier "%-2d" will CHECK fail).
+    Printf("  x%d%s%016llx", i, (i < 10) ? kDoubleSpace : kSingleSpace,
+           frame[i]);
+  }
+  Printf("\n");
+}
+
 }  // namespace __hwasan
diff --git a/lib/hwasan/hwasan_report.h b/lib/hwasan/hwasan_report.h
index 6fc53ecc5..f03eb7a69 100644
--- a/lib/hwasan/hwasan_report.h
+++ b/lib/hwasan/hwasan_report.h
@@ -22,11 +22,11 @@ namespace __hwasan {
 
 void ReportStats();
 void ReportTagMismatch(StackTrace *stack, uptr addr, uptr access_size,
-                       bool is_store, bool fatal);
+                       bool is_store, bool fatal, uptr *registers_frame);
 void ReportInvalidFree(StackTrace *stack, uptr addr);
 void ReportTailOverwritten(StackTrace *stack, uptr addr, uptr orig_size,
                            uptr tail_size, const u8 *expected);
-
+void ReportRegisters(uptr *registers_frame, uptr pc);
 void ReportAtExitStatistics();
 
 
diff --git a/lib/hwasan/hwasan_tag_mismatch_aarch64.S b/lib/hwasan/hwasan_tag_mismatch_aarch64.S
new file mode 100644
index 000000000..dbc9cc93b
--- /dev/null
+++ b/lib/hwasan/hwasan_tag_mismatch_aarch64.S
@@ -0,0 +1,108 @@
+#include "sanitizer_common/sanitizer_asm.h"
+
+// The content of this file is AArch64-only:
+#if defined(__aarch64__)
+
+// The responsibility of the HWASan entry point in compiler-rt is to primarily
+// readjust the stack from the callee and save the current register values to
+// the stack.
+// This entry point function should be called from a __hwasan_check_* symbol.
+// These are generated during a lowering pass in the backend, and are found in
+// AArch64AsmPrinter::EmitHwasanMemaccessSymbols(). Please look there for
+// further information.
+// The __hwasan_check_* caller of this function should have expanded the stack
+// and saved the previous values of x0, x1, x29, and x30. This function will
+// "consume" these saved values and treats it as part of its own stack frame.
+// In this sense, the __hwasan_check_* callee and this function "share" a stack
+// frame. This allows us to omit having unwinding information (.cfi_*) present
+// in every __hwasan_check_* function, therefore reducing binary size. This is
+// particularly important as hwasan_check_* instances are duplicated in every
+// translation unit where HWASan is enabled.
+// This function calls HwasanTagMismatch to step back into the C++ code that
+// completes the stack unwinding and error printing. This function is is not
+// permitted to return.
+
+
+// Frame from __hwasan_check_:
+// |              ...                |
+// |              ...                |
+// | Previous stack frames...        |
+// +=================================+
+// | Unused 8-bytes for maintaining  |
+// | 16-byte SP alignment.           |
+// +---------------------------------+
+// | Return address (x30) for caller |
+// | of __hwasan_check_*.            |
+// +---------------------------------+
+// | Frame address (x29) for caller  |
+// | of __hwasan_check_*             |
+// +---------------------------------+ <-- [SP + 232]
+// |              ...                |
+// |                                 |
+// | Stack frame space for x2 - x28. |
+// |                                 |
+// |              ...                |
+// +---------------------------------+ <-- [SP + 16]
+// |                                 |
+// | Saved x1, as __hwasan_check_*   |
+// | clobbers it.                    |
+// +---------------------------------+
+// | Saved x0, likewise above.       |
+// +---------------------------------+ <-- [x30 / SP]
+
+// This function takes two arguments:
+//   * x0: The address of read/write instruction that caused HWASan check fail.
+//   * x1: The tag size.
+
+.section .text
+.file "hwasan_tag_mismatch_aarch64.S"
+.global __hwasan_tag_mismatch
+.type __hwasan_tag_mismatch, %function
+__hwasan_tag_mismatch:
+  CFI_STARTPROC
+
+  // Set the CFA to be the return address for caller of __hwasan_check_*. Note
+  // that we do not emit CFI predicates to describe the contents of this stack
+  // frame, as this proxy entry point should never be debugged. The contents
+  // are static and are handled by the unwinder after calling
+  // __hwasan_tag_mismatch. The frame pointer is already correctly setup
+  // by __hwasan_check_*.
+  add x29, sp, #232
+  CFI_DEF_CFA(w29, 16)
+  CFI_OFFSET(w30, -8)
+  CFI_OFFSET(w29, -16)
+
+  // Save the rest of the registers into the preallocated space left by
+  // __hwasan_check.
+  str     x28,      [sp, #224]
+  stp     x26, x27, [sp, #208]
+  stp     x24, x25, [sp, #192]
+  stp     x22, x23, [sp, #176]
+  stp     x20, x21, [sp, #160]
+  stp     x18, x19, [sp, #144]
+  stp     x16, x17, [sp, #128]
+  stp     x14, x15, [sp, #112]
+  stp     x12, x13, [sp, #96]
+  stp     x10, x11, [sp, #80]
+  stp     x8,  x9,  [sp, #64]
+  stp     x6,  x7,  [sp, #48]
+  stp     x4,  x5,  [sp, #32]
+  stp     x2,  x3,  [sp, #16]
+
+  // Pass the address of the frame to __hwasan_tag_mismatch_stub, so that it can
+  // extract the saved registers from this frame without having to worry about
+  // finding this frame.
+  mov x2, sp
+
+  bl __hwasan_tag_mismatch_stub
+  CFI_ENDPROC
+
+.Lfunc_end0:
+  .size __hwasan_tag_mismatch, .Lfunc_end0-__hwasan_tag_mismatch
+
+.addrsig
+
+#endif  // defined(__aarch64__)
+
+// We do not need executable stack.
+NO_EXEC_STACK_DIRECTIVE
diff --git a/test/hwasan/TestCases/register-dump-read.c b/test/hwasan/TestCases/register-dump-read.c
new file mode 100644
index 000000000..19bf03f5d
--- /dev/null
+++ b/test/hwasan/TestCases/register-dump-read.c
@@ -0,0 +1,43 @@
+// RUN: %clang_hwasan -ffixed-x10 -ffixed-x20 -ffixed-x27 -O0 %s -o %t && not %run %t 2>&1 | FileCheck %s --check-prefixes=CHECK
+// RUN: %clang_hwasan -ffixed-x10 -ffixed-x20 -ffixed-x27 -O1 %s -o %t && not %run %t 2>&1 | FileCheck %s --check-prefixes=CHECK
+// RUN: %clang_hwasan -ffixed-x10 -ffixed-x20 -ffixed-x27 -O2 %s -o %t && not %run %t 2>&1 | FileCheck %s --check-prefixes=CHECK
+// RUN: %clang_hwasan -ffixed-x10 -ffixed-x20 -ffixed-x27 -O3 %s -o %t && not %run %t 2>&1 | FileCheck %s --check-prefixes=CHECK
+// REQUIRES: aarch64-target-arch
+
+// RUN: %clang_hwasan -ffixed-x10 -ffixed-x20 -ffixed-x27 -O2 %s -o %t && not %env_hwasan_opts=fast_unwind_on_fatal=true %run %t 2>&1 | FileCheck %s --check-prefixes=CHECK
+// RUN: %clang_hwasan -ffixed-x10 -ffixed-x20 -ffixed-x27 -O2 %s -o %t && not %env_hwasan_opts=fast_unwind_on_fatal=false %run %t 2>&1 | FileCheck %s --check-prefixes=CHECK
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <sanitizer/hwasan_interface.h>
+
+int main() {
+  __hwasan_enable_allocator_tagging();
+  char * volatile x = (char*) malloc(10);
+  asm volatile("mov x10, #0x2222\n"
+               "mov x20, #0x3333\n"
+               "mov x27, #0x4444\n");
+  return x[16];
+
+  // CHECK: ERROR: HWAddressSanitizer:
+  // CHECK: #0 {{.*}} in main {{.*}}register-dump-read.c:[[@LINE-3]]
+
+  // Developer note: FileCheck really doesn't like when you have a regex that
+  // ends with a '}' character, e.g. the regex "[0-9]{10}" will fail, because
+  // the closing '}' fails as an "unbalanced regex". We work around this by
+  // encasing the trailing space after a register, or the end-of-line specifier.
+
+  // CHECK: Registers where the failure occurred
+  // CHECK-NEXT: x0{{[ ]+[0-9a-f]{16}[ ]}}x1{{[ ]+[0-9a-f]{16}[ ]}}x2{{[ ]+[0-9a-f]{16}[ ]}}x3{{[ ]+[0-9a-f]{16}$}}
+  // CHECK-NEXT: x4{{[ ]+[0-9a-f]{16}[ ]}}x5{{[ ]+[0-9a-f]{16}[ ]}}x6{{[ ]+[0-9a-f]{16}[ ]}}x7{{[ ]+[0-9a-f]{16}$}}
+  // CHECK-NEXT: x8{{[ ]+[0-9a-f]{16}[ ]}}x9{{[ ]+[0-9a-f]{16}[ ]}}
+  // CHECK-SAME: x10 0000000000002222
+  // CHECK-SAME: x11{{[ ]+[0-9a-f]{16}$}}
+  // CHECK-NEXT: x12{{[ ]+[0-9a-f]{16}[ ]}}x13{{[ ]+[0-9a-f]{16}[ ]}}x14{{[ ]+[0-9a-f]{16}[ ]}}x15{{[ ]+[0-9a-f]{16}$}}
+  // CHECK-NEXT: x16{{[ ]+[0-9a-f]{16}[ ]}}x17{{[ ]+[0-9a-f]{16}[ ]}}x18{{[ ]+[0-9a-f]{16}[ ]}}x19{{[ ]+[0-9a-f]{16}$}}
+  // CHECK-NEXT: x20 0000000000003333
+  // CHECK-SAME: x21{{[ ]+[0-9a-f]{16}[ ]}}x22{{[ ]+[0-9a-f]{16}[ ]}}x23{{[ ]+[0-9a-f]{16}$}}
+  // CHECK-NEXT: x24{{[ ]+[0-9a-f]{16}[ ]}}x25{{[ ]+[0-9a-f]{16}[ ]}}x26{{[ ]+[0-9a-f]{16}[ ]}}
+  // CHECK-SAME: x27 0000000000004444
+  // CHECK-NEXT: x28{{[ ]+[0-9a-f]{16}[ ]}}x29{{[ ]+[0-9a-f]{16}[ ]}}x30{{[ ]+[0-9a-f]{16}$}}
+}