PR_SET_TAGGED_ADDR_CTRL(2const)                PR_SET_TAGGED_ADDR_CTRL(2const)

NAME
       PR_SET_TAGGED_ADDR_CTRL - control support for passing tagged user-space
       addresses to the kernel

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <linux/prctl.h>  /* Definition of PR_* constants */
       #include <sys/prctl.h>

       int prctl(PR_SET_TAGGED_ADDR_CTRL, long mode, 0L, 0L, 0L);

DESCRIPTION
       Controls support for passing tagged user-space addresses to the kernel
       (i.e., addresses where bits 56--63 are not all zero).

       The level of support is selected by support, which can be one of the
       following:

       0L     Addresses that are passed for the purpose of being dereferenced
              by the kernel must be untagged.

       PR_TAGGED_ADDR_ENABLE
              Addresses that are passed for the purpose of being dereferenced
              by the kernel may be tagged, with the exceptions summarized
              below.

       On success, the mode specified in mode is set for the calling thread.

       If prctl(PR_SET_TAGGED_ADDR_CTRL, 0L, 0L, 0L, 0L) fails with EINVAL,
       then all addresses passed to the kernel must be untagged.

       Irrespective of which mode is set, addresses passed to certain
       interfaces must always be untagged:

       o  brk(2), mmap(2), shmat(2), shmdt(2), and the new_address argument of
          mremap(2).

          (Prior to Linux 5.6 these accepted tagged addresses, but the
          behaviour may not be what you expect.  Don't rely on it.)

       o  `polymorphic' interfaces that accept pointers to arbitrary types
          cast to a void * or other generic type, specifically prctl(),
          ioctl(2), and in general setsockopt(2) (only certain specific
          setsockopt(2) options allow tagged addresses).

       This list of exclusions may shrink when moving from one kernel version
       to a later kernel version.  While the kernel may make some guarantees
       for backwards compatibility reasons, for the purposes of new software
       the effect of passing tagged addresses to these interfaces is
       unspecified.

       The mode set by this call is inherited across fork(2) and clone(2).
       The mode is reset by execve(2) to 0 (i.e., tagged addresses not
       permitted in the user/kernel ABI).

RETURN VALUE
       On success, 0 is returned.  On error, -1 is returned, and errno is set
       to indicate the error.

ERRORS
       EINVAL mode is invalid or unsupported.

       EINVAL This feature is disabled via /proc/sys/abi/tagged_addr_disabled.

FILES
       /proc/sys/abi/tagged_addr_disabled

STANDARDS
       Linux.  arm64 only.

HISTORY
       Linux 5.4 (arm64).

CAVEATS
       This call is primarily intended for use by the run-time environment.  A
       successful PR_SET_TAGGED_ADDR_CTRL call elsewhere may crash the calling
       process.  The conditions for using it safely are complex and system-
       dependent.  Don't use it unless you know what you are doing.

SEE ALSO
       prctl(2), PR_SET_TAGGED_ADDR_CTRL(2const)

       For more information, see the kernel source file
       Documentation/arm64/tagged-address-abi.rst.

Linux man-pages 6.10              2024-07-23   PR_SET_TAGGED_ADDR_CTRL(2const)