llvm/lib/Target/AArch64/AArch64PointerAuth.h

   1 //===-- AArch64PointerAuth.h -- Harden code using PAuth ---------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef LLVM_LIB_TARGET_AARCH64_AARCH64POINTERAUTH_H
  10 #define LLVM_LIB_TARGET_AARCH64_AARCH64POINTERAUTH_H
  11
  12 #include "llvm/CodeGen/MachineBasicBlock.h"
  13 #include "llvm/CodeGen/Register.h"
  14
  15 namespace llvm {
  16 namespace AArch64PAuth {
  17
  18 /// Variants of check performed on an authenticated pointer.
  19 ///
  20 /// In cases such as authenticating the LR value when performing a tail call
  21 /// or when re-signing a signed pointer with a different signing schema,
  22 /// a failed authentication may not generate an exception on its own and may
  23 /// create an authentication or signing oracle if not checked explicitly.
  24 ///
  25 /// A number of check methods modify control flow in a similar way by
  26 /// rewriting the code
  27 ///
  28 /// ```
  29 ///   <authenticate LR>
  30 ///   <more instructions>
  31 /// ```
  32 ///
  33 /// as follows:
  34 ///
  35 /// ```
  36 ///   <authenticate LR>
  37 ///   <method-specific checker>
  38 /// on_fail:
  39 ///   brk <code>
  40 /// on_success:
  41 ///   <more instructions>
  42 ///
  43 /// ```
  44 enum class AuthCheckMethod {
  45   /// Do not check the value at all
  46   None,
  47
  48   /// Perform a load to a temporary register
  49   DummyLoad,
  50
  51   /// Check by comparing bits 62 and 61 of the authenticated address.
  52   ///
  53   /// This method modifies control flow and inserts the following checker:
  54   ///
  55   /// ```
  56   ///   eor Xtmp, Xn, Xn, lsl #1
  57   ///   tbz Xtmp, #62, on_success
  58   /// ```
  59   HighBitsNoTBI,
  60
  61   /// Check by comparing the authenticated value with an XPAC-ed one without
  62   /// using PAuth instructions not encoded as HINT. Can only be applied to LR.
  63   ///
  64   /// This method modifies control flow and inserts the following checker:
  65   ///
  66   /// ```
  67   ///   mov Xtmp, LR
  68   ///   xpaclri           ; encoded as "hint #7"
  69   ///   ; Note: at this point, the LR register contains the address as if
  70   ///   ; the authentication succeeded and the temporary register contains the
  71   ///   ; *real* result of authentication.
  72   ///   cmp Xtmp, LR
  73   ///   b.eq on_success
  74   /// ```
  75   XPACHint,
  76
  77   /// Similar to XPACHint but using Armv8.3-only XPAC instruction, thus
  78   /// not restricted to LR:
  79   /// ```
  80   ///   mov Xtmp, Xn
  81   ///   xpac(i|d) Xn
  82   ///   cmp Xtmp, Xn
  83   ///   b.eq on_success
  84   /// ```
  85   XPAC,
  86 };
  87
  88 #define AUTH_CHECK_METHOD_CL_VALUES_COMMON                                     \
  89   clEnumValN(AArch64PAuth::AuthCheckMethod::None, "none",                      \
  90              "Do not check authenticated address"),                            \
  91       clEnumValN(AArch64PAuth::AuthCheckMethod::DummyLoad, "load",             \
  92                  "Perform dummy load from authenticated address"),             \
  93       clEnumValN(                                                              \
  94           AArch64PAuth::AuthCheckMethod::HighBitsNoTBI, "high-bits-notbi",     \
  95           "Compare bits 62 and 61 of address (TBI should be disabled)"),       \
  96       clEnumValN(AArch64PAuth::AuthCheckMethod::XPAC, "xpac",                  \
  97                  "Compare with the result of XPAC (requires Armv8.3-a)")
  98
  99 #define AUTH_CHECK_METHOD_CL_VALUES_LR                                         \
 100       AUTH_CHECK_METHOD_CL_VALUES_COMMON,                                      \
 101       clEnumValN(AArch64PAuth::AuthCheckMethod::XPACHint, "xpac-hint",         \
 102                  "Compare with the result of XPACLRI")
 103
 104 /// Returns the number of bytes added by checkAuthenticatedRegister.
 105 unsigned getCheckerSizeInBytes(AuthCheckMethod Method);
 106
 107 } // end namespace AArch64PAuth
 108 } // end namespace llvm
 109
 110 #endif