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Diffstat (limited to '')
| -rw-r--r-- | Documentation/arm64/tagged-address-abi.rst | 32 |
1 files changed, 24 insertions, 8 deletions
diff --git a/Documentation/arm64/tagged-address-abi.rst b/Documentation/arm64/tagged-address-abi.rst index 4a9d9c794ee5..540a1d4fc6c9 100644 --- a/Documentation/arm64/tagged-address-abi.rst +++ b/Documentation/arm64/tagged-address-abi.rst @@ -40,19 +40,29 @@ space obtained in one of the following ways: during creation and with the same restrictions as for ``mmap()`` above (e.g. data, bss, stack). -The AArch64 Tagged Address ABI has two stages of relaxation depending +The AArch64 Tagged Address ABI has two stages of relaxation depending on how the user addresses are used by the kernel: 1. User addresses not accessed by the kernel but used for address space management (e.g. ``mprotect()``, ``madvise()``). The use of valid - tagged pointers in this context is allowed with the exception of - ``brk()``, ``mmap()`` and the ``new_address`` argument to - ``mremap()`` as these have the potential to alias with existing - user addresses. + tagged pointers in this context is allowed with these exceptions: - NOTE: This behaviour changed in v5.6 and so some earlier kernels may - incorrectly accept valid tagged pointers for the ``brk()``, - ``mmap()`` and ``mremap()`` system calls. + - ``brk()``, ``mmap()`` and the ``new_address`` argument to + ``mremap()`` as these have the potential to alias with existing + user addresses. + + NOTE: This behaviour changed in v5.6 and so some earlier kernels may + incorrectly accept valid tagged pointers for the ``brk()``, + ``mmap()`` and ``mremap()`` system calls. + + - The ``range.start``, ``start`` and ``dst`` arguments to the + ``UFFDIO_*`` ``ioctl()``s used on a file descriptor obtained from + ``userfaultfd()``, as fault addresses subsequently obtained by reading + the file descriptor will be untagged, which may otherwise confuse + tag-unaware programs. + + NOTE: This behaviour changed in v5.14 and so some earlier kernels may + incorrectly accept valid tagged pointers for this system call. 2. User addresses accessed by the kernel (e.g. ``write()``). This ABI relaxation is disabled by default and the application thread needs to @@ -113,6 +123,12 @@ ABI relaxation: - ``shmat()`` and ``shmdt()``. +- ``brk()`` (since kernel v5.6). + +- ``mmap()`` (since kernel v5.6). + +- ``mremap()``, the ``new_address`` argument (since kernel v5.6). + Any attempt to use non-zero tagged pointers may result in an error code being returned, a (fatal) signal being raised, or other modes of failure. |