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:

       •  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.)

       •  ‘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 6.9.1                              2024-06-01                    PR_SET_TAGGED_ADDR_CTRL(2const)