xref: /freebsd/contrib/llvm-project/clang/lib/Headers/ptrauth.h (revision 36b606ae6aa4b24061096ba18582e0a08ccd5dba)

/*===---- ptrauth.h - Pointer authentication -------------------------------===
 *
 * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 * See https://llvm.org/LICENSE.txt for license information.
 * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 *
 *===-----------------------------------------------------------------------===
 */

#ifndef __PTRAUTH_H
#define __PTRAUTH_H

typedef enum {
  ptrauth_key_asia = 0,
  ptrauth_key_asib = 1,
  ptrauth_key_asda = 2,
  ptrauth_key_asdb = 3,

  /* A process-independent key which can be used to sign code pointers. */
  ptrauth_key_process_independent_code = ptrauth_key_asia,

  /* A process-specific key which can be used to sign code pointers. */
  ptrauth_key_process_dependent_code = ptrauth_key_asib,

  /* A process-independent key which can be used to sign data pointers. */
  ptrauth_key_process_independent_data = ptrauth_key_asda,

  /* A process-specific key which can be used to sign data pointers. */
  ptrauth_key_process_dependent_data = ptrauth_key_asdb,

  /* The key used to sign C function pointers.
     The extra data is always 0. */
  ptrauth_key_function_pointer = ptrauth_key_process_independent_code,

  /* The key used to sign C++ v-table pointers.
     The extra data is always 0. */
  ptrauth_key_cxx_vtable_pointer = ptrauth_key_process_independent_data,

  /* Other pointers signed under the ABI use private ABI rules. */

} ptrauth_key;

/* An integer type of the appropriate size for a discriminator argument. */
typedef __UINTPTR_TYPE__ ptrauth_extra_data_t;

/* An integer type of the appropriate size for a generic signature. */
typedef __UINTPTR_TYPE__ ptrauth_generic_signature_t;

/* A signed pointer value embeds the original pointer together with
   a signature that attests to the validity of that pointer.  Because
   this signature must use only "spare" bits of the pointer, a
   signature's validity is probabilistic in practice: it is unlikely
   but still plausible that an invalidly-derived signature will
   somehow equal the correct signature and therefore successfully
   authenticate.  Nonetheless, this scheme provides a strong degree
   of protection against certain kinds of attacks. */

/* Authenticating a pointer that was not signed with the given key
   and extra-data value will (likely) fail by trapping. */

/* The null function pointer is always the all-zero bit pattern.
   Signing an all-zero bit pattern will embed a (likely) non-zero
   signature in the result, and so the result will not seem to be
   a null function pointer.  Authenticating this value will yield
   a null function pointer back.  However, authenticating an
   all-zero bit pattern will probably fail, because the
   authentication will expect a (likely) non-zero signature to
   embedded in the value.

   Because of this, if a pointer may validly be null, you should
   check for null before attempting to authenticate it with one
   of these intrinsics.  This is not necessary when using the
   __ptrauth qualifier; the compiler will perform this check
   automatically. */

#if __has_feature(ptrauth_intrinsics)

/* Strip the signature from a value without authenticating it.

   If the value is a function pointer, the result will not be a
   legal function pointer because of the missing signature, and
   attempting to call it will result in an authentication failure.

   The value must be an expression of pointer type.
   The key must be a constant expression of type ptrauth_key.
   The result will have the same type as the original value. */
#define ptrauth_strip(__value, __key) __builtin_ptrauth_strip(__value, __key)

/* Blend a constant discriminator into the given pointer-like value
   to form a new discriminator.  Not all bits of the inputs are
   guaranteed to contribute to the result.

   On arm64e, the integer must fall within the range of a uint16_t;
   other bits may be ignored.

   For the purposes of ptrauth_sign_constant, the result of calling
   this function is considered a constant expression if the arguments
   are constant.  Some restrictions may be imposed on the pointer.

   The first argument must be an expression of pointer type.
   The second argument must be an expression of integer type.
   The result will have type uintptr_t. */
#define ptrauth_blend_discriminator(__pointer, __integer)                      \
  __builtin_ptrauth_blend_discriminator(__pointer, __integer)

/* Return a signed pointer for a constant address in a manner which guarantees
   a non-attackable sequence.

   The value must be a constant expression of pointer type which evaluates to
   a non-null pointer.
   The key must be a constant expression of type ptrauth_key.
   The extra data must be a constant expression of pointer or integer type;
   if an integer, it will be coerced to ptrauth_extra_data_t.
   The result will have the same type as the original value.

   This can be used in constant expressions.  */
#define ptrauth_sign_constant(__value, __key, __data)                          \
  __builtin_ptrauth_sign_constant(__value, __key, __data)

/* Add a signature to the given pointer value using a specific key,
   using the given extra data as a salt to the signing process.

   This operation does not authenticate the original value and is
   therefore potentially insecure if an attacker could possibly
   control that value.

   The value must be an expression of pointer type.
   The key must be a constant expression of type ptrauth_key.
   The extra data must be an expression of pointer or integer type;
   if an integer, it will be coerced to ptrauth_extra_data_t.
   The result will have the same type as the original value. */
#define ptrauth_sign_unauthenticated(__value, __key, __data)                   \
  __builtin_ptrauth_sign_unauthenticated(__value, __key, __data)

/* Authenticate a pointer using one scheme and resign it using another.

   If the result is subsequently authenticated using the new scheme, that
   authentication is guaranteed to fail if and only if the initial
   authentication failed.

   The value must be an expression of pointer type.
   The key must be a constant expression of type ptrauth_key.
   The extra data must be an expression of pointer or integer type;
   if an integer, it will be coerced to ptrauth_extra_data_t.
   The result will have the same type as the original value.

   This operation is guaranteed to not leave the intermediate value
   available for attack before it is re-signed.

   Do not pass a null pointer to this function. A null pointer
   will not successfully authenticate.

   This operation traps if the authentication fails. */
#define ptrauth_auth_and_resign(__value, __old_key, __old_data, __new_key,     \
                                __new_data)                                    \
  __builtin_ptrauth_auth_and_resign(__value, __old_key, __old_data, __new_key, \
                                    __new_data)

/* Authenticate a pointer using one scheme and resign it as a C
   function pointer.

   If the result is subsequently authenticated using the new scheme, that
   authentication is guaranteed to fail if and only if the initial
   authentication failed.

   The value must be an expression of function pointer type.
   The key must be a constant expression of type ptrauth_key.
   The extra data must be an expression of pointer or integer type;
   if an integer, it will be coerced to ptrauth_extra_data_t.
   The result will have the same type as the original value.

   This operation is guaranteed to not leave the intermediate value
   available for attack before it is re-signed. Additionally, if this
   expression is used syntactically as the function expression in a
   call, only a single authentication will be performed. */
#define ptrauth_auth_function(__value, __old_key, __old_data)                  \
  ptrauth_auth_and_resign(__value, __old_key, __old_data,                      \
                          ptrauth_key_function_pointer, 0)

/* Authenticate a data pointer.

   The value must be an expression of non-function pointer type.
   The key must be a constant expression of type ptrauth_key.
   The extra data must be an expression of pointer or integer type;
   if an integer, it will be coerced to ptrauth_extra_data_t.
   The result will have the same type as the original value.

   This operation traps if the authentication fails. */
#define ptrauth_auth_data(__value, __old_key, __old_data)                      \
  __builtin_ptrauth_auth(__value, __old_key, __old_data)

/* Compute a constant discriminator from the given string.

   The argument must be a string literal of char character type.  The result
   has type ptrauth_extra_data_t.

   The result value is never zero and always within range for both the
   __ptrauth qualifier and ptrauth_blend_discriminator.

   This can be used in constant expressions.
*/
#define ptrauth_string_discriminator(__string)                                 \
  __builtin_ptrauth_string_discriminator(__string)

/* Compute a constant discriminator from the given type.

   The result can be used as the second argument to
   ptrauth_blend_discriminator or the third argument to the
   __ptrauth qualifier.  It has type size_t.

   If the type is a C++ member function pointer type, the result is
   the discriminator used to signed member function pointers of that
   type.  If the type is a function, function pointer, or function
   reference type, the result is the discriminator used to sign
   functions of that type.  It is ill-formed to use this macro with any
   other type.

   A call to this function is an integer constant expression. */
#define ptrauth_type_discriminator(__type)                                     \
  __builtin_ptrauth_type_discriminator(__type)

/* Compute a signature for the given pair of pointer-sized values.
   The order of the arguments is significant.

   Like a pointer signature, the resulting signature depends on
   private key data and therefore should not be reliably reproducible
   by attackers.  That means that this can be used to validate the
   integrity of arbitrary data by storing a signature for that data
   alongside it, then checking that the signature is still valid later.
   Data which exceeds two pointers in size can be signed by either
   computing a tree of generic signatures or just signing an ordinary
   cryptographic hash of the data.

   The result has type ptrauth_generic_signature_t.  However, it may
   not have as many bits of entropy as that type's width would suggest;
   some implementations are known to compute a compressed signature as
   if the arguments were a pointer and a discriminator.

   The arguments must be either pointers or integers; if integers, they
   will be coerce to uintptr_t. */
#define ptrauth_sign_generic_data(__value, __data)                             \
  __builtin_ptrauth_sign_generic_data(__value, __data)

/* C++ vtable pointer signing class attribute */
#define ptrauth_cxx_vtable_pointer(key, address_discrimination,                \
                                   extra_discrimination...)                    \
  [[clang::ptrauth_vtable_pointer(key, address_discrimination,                 \
                                  extra_discrimination)]]

#else

#define ptrauth_strip(__value, __key)                                          \
  ({                                                                           \
    (void)__key;                                                               \
    __value;                                                                   \
  })

#define ptrauth_blend_discriminator(__pointer, __integer)                      \
  ({                                                                           \
    (void)__pointer;                                                           \
    (void)__integer;                                                           \
    ((ptrauth_extra_data_t)0);                                                 \
  })

#define ptrauth_sign_constant(__value, __key, __data)                          \
  ({                                                                           \
    (void)__key;                                                               \
    (void)__data;                                                              \
    __value;                                                                   \
  })

#define ptrauth_sign_unauthenticated(__value, __key, __data)                   \
  ({                                                                           \
    (void)__key;                                                               \
    (void)__data;                                                              \
    __value;                                                                   \
  })

#define ptrauth_auth_and_resign(__value, __old_key, __old_data, __new_key,     \
                                __new_data)                                    \
  ({                                                                           \
    (void)__old_key;                                                           \
    (void)__old_data;                                                          \
    (void)__new_key;                                                           \
    (void)__new_data;                                                          \
    __value;                                                                   \
  })

#define ptrauth_auth_function(__value, __old_key, __old_data)                  \
  ({                                                                           \
    (void)__old_key;                                                           \
    (void)__old_data;                                                          \
    __value;                                                                   \
  })

#define ptrauth_auth_data(__value, __old_key, __old_data)                      \
  ({                                                                           \
    (void)__old_key;                                                           \
    (void)__old_data;                                                          \
    __value;                                                                   \
  })

#define ptrauth_string_discriminator(__string)                                 \
  ({                                                                           \
    (void)__string;                                                            \
    ((ptrauth_extra_data_t)0);                                                 \
  })

#define ptrauth_type_discriminator(__type) ((ptrauth_extra_data_t)0)

#define ptrauth_sign_generic_data(__value, __data)                             \
  ({                                                                           \
    (void)__value;                                                             \
    (void)__data;                                                              \
    ((ptrauth_generic_signature_t)0);                                          \
  })


#define ptrauth_cxx_vtable_pointer(key, address_discrimination,                \
                                   extra_discrimination...)

#endif /* __has_feature(ptrauth_intrinsics) */

#endif /* __PTRAUTH_H */