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Date: Sat, 24 Mar 2012 10:17:04 +0400 From: Cyrill Gorcunov <gorcunov@...nvz.org> To: "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com> Cc: akpm@...ux-foundation.org, xemul@...allels.com, linux-man@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/2] prctl.2: Add PR_SET_MM option description On Sat, Mar 24, 2012 at 03:59:49PM +1300, Michael Kerrisk (man-pages) wrote: > > Hi Cyrill, > > I only just had a chance to look at this now and realize that this is > a patch on a patch. Could you just send me a complete patch with all > the changes? > Sure, here is it Cyrill --- From: Cyrill Gorcunov <gorcunov@...nvz.org> Date: Sat, 24 Mar 2012 10:15:28 +0400 Subject: [PATCH 2/2] prctl.2: Add PR_SET_MM option description CC: Pavel Emelyanov <xemul@...allels.com> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org> --- man2/prctl.2 | 174 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 files changed, 173 insertions(+), 1 deletions(-) diff --git a/man2/prctl.2 b/man2/prctl.2 index effad2a..de15426 100644 --- a/man2/prctl.2 +++ b/man2/prctl.2 @@ -378,6 +378,134 @@ Return the current per-process machine check kill policy. All unused .BR prctl () arguments must be zero. +.TP +.BR PR_SET_MM " (since Linux 3.3)" +Allows a user to modify certain kernel memory map descriptor fields +of the calling process. +Usually these fields are set by the kernel and dynamic loader (see +.BR ld.so (8) +for more information) and a regular application should not use this feature. +Still there are cases such as self-modifying programs, where a program might +find it useful to change its own memory map. +The kernel must be built with +.BR CONFIG_CHECKPOINT_RESTORE +option turned on, otherwise this feature will not be accessible +from a user space level. +The calling process must have +.BR CAP_SYS_RESOURCE +(see +.BR capabilities (7) +for details) capability granted. +The value in +.I arg2 +is one of the options below, while +.I arg3 +provides a new value for this option. + +.BR PR_SET_MM_START_CODE +to set the address above which program text can run. +The corresponding memory area must be readable and executable, +but not writable or shareable (see +.BR mprotect (2) +and +.BR mmap (2) +for more information). + +.BR PR_SET_MM_END_CODE +to set the address below which program text can run. +The corresponding memory area must be readable and executable, +but not writable or shareable. + +.BR PR_SET_MM_START_DATA +to set the address above which program data+bss is placed. +The corresponding memory area must be readable and writable, +but not executable or shareable. + +.B PR_SET_MM_END_DATA +to set the address below which program data+bss is placed. +The corresponding memory area must be readable and writable, +but not executable or shareable. + +.BR PR_SET_MM_START_STACK +to set the start address of the stack. +The corresponding memory area must be readable and writable. + +.BR PR_SET_MM_START_BRK +to set the address above which program heap can be expanded with +.BR brk (2) +call. +The address must not be greater than ending address of +the current program data segment, neither it may exceed +resource limit for data (see +.BR setrlimit (2) +for more information). + +.BR PR_SET_MM_BRK +to set the current +.BR brk (2) +value. +The requirements for address are the same as for +.BR PR_SET_MM_START_BRK +option. + +.BR PR_SET_MM_ARG_START +to set the address above which program command line is placed. + +.BR PR_SET_MM_ARG_END +to set the address below which program command line is placed. + +.BR PR_SET_MM_ENV_START +to set the address above which program environment is placed. + +.BR PR_SET_MM_ENV_END +to set the address below which program environment is placed. + +The address passed with +.BR PR_SET_MM_ARG_START , +.BR PR_SET_MM_ARG_END , +.BR PR_SET_MM_ENV_START , +.BR PR_SET_MM_ENV_END , +should belong to a process stack area, thus corresponding memory area +must be readable, writable and (depending on the kernel +configuration) has +.BR MAP_GROWSDOWN +attribute set (see +.BR mmap (2) +for details). + +.BR PR_SET_MM_AUXV +to set a new auxiliary vector. +The +.I arg3 +argument should provide the address of the vector. +The +.I arg4 +is the size of the vector. + +.BR PR_SET_MM_EXE_FILE +to supersede +.IR /proc/pid/exe +symbolic link with a new one pointing to a new executable file +which descriptor is provided provided in the +.I arg3 +argument. +The file descriptor should be obtaned with a regular +.BR open (2) +call. + +To change the symlink, one needs to unmap all existing +executable memory areas being created by the kernel itself +(for example the kernel usually creates at least one executable +memory area for Elf file +.IR \.text +section). + +The second limitation is that such transition can be done once +in a process life time. +Any furter attempts will be rejected. +This should help system administrators to monitor the unusual +symlinks transitions over all process running in a system. +.\" .SH "RETURN VALUE" On success, .BR PR_GET_DUMPABLE , @@ -411,7 +539,9 @@ is not recognized. is .BR PR_MCE_KILL or -.BR PR_MCE_KILL_GET , +.BR PR_MCE_KILL_GET +or +.BR PR_SET_MM , and unused .BR prctl () arguments were not specified as zero. @@ -459,6 +589,48 @@ is and the caller does not have the .B CAP_SETPCAP capability. +.TP +.B EPERM +.I option +is +.BR PR_SET_MM , +and the caller does not have the +.B CAP_SYS_RESOURCE +capability. +.TP +.B EACCES +.I option +is +.BR PR_SET_MM , +and the +.I arg3 +is +.BR PR_SET_MM_EXE_FILE , +the file is not executable one. +.TP +.B EBUSY +.I option +is +.BR PR_SET_MM , +and the +.I arg3 +is +.BR PR_SET_MM_EXE_FILE , +the second attempt to change +.I /proc/pid/exe +symlink is prohibited. +.TP +.B EBADF +.I option +is +.BR PR_SET_MM , +and the +.I arg3 +is +.BR PR_SET_MM_EXE_FILE , +the file descriptor passed in +.I arg4 +is not found. .\" The following can't actually happen, because prctl() in .\" seccomp mode will cause SIGKILL. .\" .TP -- 1.7.7.6 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at 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