mirror of https://github.com/mkerrisk/man-pages
prctl.2: Various edits and improvements to Cyrill's patch
* Wording improvements * Addition of some FIXMEs for suspicious points * Addition of various EINVAL cases Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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Michael Kerrisk
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man2/prctl.2
197
man2/prctl.2
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@ -380,131 +380,141 @@ All unused
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arguments must be zero.
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.TP
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.BR PR_SET_MM " (since Linux 3.3)"
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Allows a user to modify certain kernel memory map descriptor fields
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Modify certain kernel memory map descriptor fields
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of the calling process.
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Usually these fields are set by the kernel and dynamic loader (see
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.BR ld.so (8)
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for more information) and a regular application should not use this feature.
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Still there are cases such as self-modifying programs, where a program might
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find it useful to change its own memory map.
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The kernel must be built with
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However, there are cases, such as self-modifying programs,
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where a program might find it useful to change its own memory map.
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This feature is available only if the kernel is built with the
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.BR CONFIG_CHECKPOINT_RESTORE
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option turned on, otherwise this feature will not be accessible
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from a user space level.
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The calling process must have
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option enabled.
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The calling process must have the
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.BR CAP_SYS_RESOURCE
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(see
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.BR capabilities (7)
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for details) capability granted.
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capability.
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The value in
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.I arg2
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is one of the options below, while
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.I arg3
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provides a new value for this option.
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provides a new value for the option.
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.RS
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.TP
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.BR PR_SET_MM_START_CODE
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to set the address above which program text can run.
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Set the address above which the program text can run.
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The corresponding memory area must be readable and executable,
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but not writable or shareable (see
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but not writable or sharable (see
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.BR mprotect (2)
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and
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.BR mmap (2)
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for more information).
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.TP
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.BR PR_SET_MM_END_CODE
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to set the address below which program text can run.
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Set the address below which the program text can run.
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The corresponding memory area must be readable and executable,
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but not writable or shareable.
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but not writable or sharable.
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.TP
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.BR PR_SET_MM_START_DATA
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to set the address above which program data+bss is placed.
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Set the address above which initialized and
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uninitialized (bss) data are placed.
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The corresponding memory area must be readable and writable,
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but not executable or shareable.
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but not executable or sharable.
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.TP
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.B PR_SET_MM_END_DATA
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to set the address below which program data+bss is placed.
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Set the address below which initialized and
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uninitialized (bss) data are placed.
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The corresponding memory area must be readable and writable,
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but not executable or shareable.
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but not executable or sharable.
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.TP
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.BR PR_SET_MM_START_STACK
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to set the start address of the stack.
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Set the start address of the stack.
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The corresponding memory area must be readable and writable.
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.TP
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.BR PR_SET_MM_START_BRK
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to set the address above which program heap can be expanded with
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Set the address above which the program heap can be expanded with
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.BR brk (2)
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call.
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The address must not be greater than ending address of
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the current program data segment, neither it may exceed
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resource limit for data (see
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.BR setrlimit (2)
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for more information).
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.\" FIXME In the next sentence, shouldn't "not be greater" be "be greater"?
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The address must not be greater than the ending address of
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the current program data segment.
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.\" FIXME I completely rewrote the following sentence. Is it okay?
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.\" FIXME Is the following error documented in ERRORS?
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In addition, the combined size of the resulting heap and
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the size of the data segment can't exceed the
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.BR RLIMIT_DATA
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resource limit (see
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.BR setrlimit (2)).
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.TP
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.BR PR_SET_MM_BRK
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to set the current
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Set the current
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.BR brk (2)
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value.
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The requirements for address are the same as for
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The requirements for the address are the same as for the
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.BR PR_SET_MM_START_BRK
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option.
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.\" FIXME Delete or comment out the following? (until ========)
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.\" None of the following constants exist in current kernel source
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.\" What is the state of the kernel patches for these?
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.TP
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.BR PR_SET_MM_ARG_START
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to set the address above which program command line is placed.
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Set the address above which the program command line is placed.
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.TP
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.BR PR_SET_MM_ARG_END
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to set the address below which program command line is placed.
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Set the address below which the program command line is placed.
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.TP
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.BR PR_SET_MM_ENV_START
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to set the address above which program environment is placed.
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Set the address above which the program environment is placed.
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.TP
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.BR PR_SET_MM_ENV_END
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to set the address below which program environment is placed.
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Set the address below which the program environment is placed.
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.IP
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The address passed with
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.BR PR_SET_MM_ARG_START ,
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.BR PR_SET_MM_ARG_END ,
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.BR PR_SET_MM_ENV_START ,
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.BR PR_SET_MM_ENV_END ,
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should belong to a process stack area, thus corresponding memory area
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must be readable, writable and (depending on the kernel
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configuration) has
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and
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.BR PR_SET_MM_ENV_END
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should belong to a process stack area.
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Thus, the corresponding memory area must be readable, writable, and
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(depending on the kernel configuration) have the
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.BR MAP_GROWSDOWN
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attribute set (see
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.BR mmap (2)
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for details).
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.BR mmap (2)).
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.TP
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.BR PR_SET_MM_AUXV
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to set a new auxiliary vector.
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Set a new auxiliary vector.
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The
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.I arg3
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argument should provide the address of the vector.
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The
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.I arg4
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is the size of the vector.
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.TP
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.BR PR_SET_MM_EXE_FILE
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to supersede
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Supersede the
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.IR /proc/pid/exe
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symbolic link with a new one pointing to a new executable file
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which descriptor is provided provided in the
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identified by the file descriptor provided in
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.I arg3
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argument.
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The file descriptor should be obtaned with a regular
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The file descriptor should be obtained with a regular
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.BR open (2)
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call.
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To change the symlink, one needs to unmap all existing
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executable memory areas being created by the kernel itself
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.IP
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To change the symbolic link, one needs to unmap all existing
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executable memory areas, including those created by the kernel itself
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(for example the kernel usually creates at least one executable
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memory area for Elf file
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memory area for the ELF
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.IR \.text
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section).
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The second limitation is that such transition can be done once
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.IP
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The second limitation is that such transitions can be done only once
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in a process life time.
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Any furter attempts will be rejected.
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Any further attempts will be rejected.
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This should help system administrators to monitor the unusual
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symlinks transitions over all process running in a system.
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symbolic-link transitions over all process running in a system.
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.\" ========== END FIXME
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.RE
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.\"
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.SH "RETURN VALUE"
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On success,
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@ -559,6 +569,48 @@ or
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.BR PR_SET_SECCOMP ,
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and the kernel was not configured with
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.BR CONFIG_SECCOMP .
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.\" FIXME I added the following lengthy EINVAL entry. Is it correct?
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.TP
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.B EINVAL
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.I option
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is
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.BR PR_SET_MM ,
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and one of the following is true
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.RS
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.IP * 3
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.I arg4
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or
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.I arg5
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is nonzero;
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.IP *
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.I arg3
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is greater than
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.B TASK_SIZE
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(the limit on the size of the user address space for this architecture);
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.IP *
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.I arg2
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is
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.BR PR_SET_MM_START_CODE ,
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.BR PR_SET_MM_END_CODE ,
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.BR PR_SET_MM_START_DATA ,
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.BR PR_SET_MM_END_DATA ,
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or
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.BR PR_SET_MM_START_STACK,
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and the permissions of the corresponding memory area are not as required;
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.IP *
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.I arg2
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is
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.BR PR_SET_MM_START_BRK
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or
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.BR PR_SET_MM_BRK ,
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and
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.I arg3
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.\" FIXME Is the following correct (see earlier comment)
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is less than or equal to the end of the data segment
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or specifies a value that would cause the
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.B RLIMIT_DATA
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resource limit to be exceeded.
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.RE
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.TP
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.B EPERM
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.I option
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@ -602,35 +654,36 @@ capability.
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.I option
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is
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.BR PR_SET_MM ,
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and the
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and
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.I arg3
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is
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.\" FIXME PR_SET_MM_EXE_FILE is not in the kernel sources
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.BR PR_SET_MM_EXE_FILE ,
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the file is not executable one.
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the file is not executable.
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.TP
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.B EBUSY
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.I option
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is
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.BR PR_SET_MM ,
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and the
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.I arg3
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is
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.\" FIXME PR_SET_MM_EXE_FILE is not in the kernel sources
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.BR PR_SET_MM_EXE_FILE ,
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the second attempt to change
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and this the second attempt to change the
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.I /proc/pid/exe
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symlink is prohibited.
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symbolic link, which is prohibited.
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.TP
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.B EBADF
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.I option
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is
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.BR PR_SET_MM ,
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and the
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.I arg3
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is
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.\" FIXME PR_SET_MM_EXE_FILE is not in the kernel sources
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.BR PR_SET_MM_EXE_FILE ,
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the file descriptor passed in
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and the file descriptor passed in
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.I arg4
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is not found.
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is not valid.
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.\" The following can't actually happen, because prctl() in
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.\" seccomp mode will cause SIGKILL.
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.\" .TP
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