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prctl.2: update seccomp sections for mode 2 (BPF) 

This adds a short summary of the arguments used
for "mode 2" (BPF) seccomp.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Kees Cook 2012-10-22 06:28:15 +02:00 committed by Michael Kerrisk
parent d796c68d5a
commit 34447828c4
1 changed files with 30 additions and 10 deletions
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40
man2/prctl.2
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@ -41,11 +41,12 @@
.\" 2012-04 Cyrill Gorcunov, Document PR_SET_MM
.\" 2012-04-25 Michael Kerrisk, Document PR_TASK_PERF_EVENTS_DISABLE and
.\" PR_TASK_PERF_EVENTS_ENABLE
.\" 2012-09-20 Kees Cook, update PR_SET_SECCOMP for mode 2
.\"
.\" FIXME: Document PR_SET_TIMERSLACK and PR_GET_TIMERSLACK (new in 2.6.28)
.\" commit 6976675d94042fbd446231d1bd8b7de71a980ada
.\"
.TH PRCTL 2 2012-04-23 "Linux" "Linux Programmer's Manual"
.TH PRCTL 2 2012-10-22 "Linux" "Linux Programmer's Manual"
.SH NAME
prctl \- operations on a process
.SH SYNOPSIS
@ -235,11 +236,17 @@ in the location pointed to by
.\" See http://thread.gmane.org/gmane.linux.kernel/542632
.\" [PATCH 0 of 2] seccomp updates
.\" andrea@cpushare.com
Set the secure computing mode for the calling thread.
In the current implementation,
Set the secure computing mode for the calling thread, to limit
the available syscalls.
The seccomp mode is selected via
.IR arg2 .
(The seccomp constants are defined in
.IR <linux/seccomp.h> .)
With
.IR arg2
must be 1.
After the secure computing mode has been set to 1,
set to
.BR SECCOMP_MODE_STRICT
the only system calls that the thread is permitted to make are
.BR read (2),
.BR write (2),
@ -249,22 +256,35 @@ and
Other system calls result in the delivery of a
.BR SIGKILL
signal.
Secure computing mode is useful for number-crunching applications
Strict secure computing mode is useful for number-crunching applications
that may need to execute untrusted byte code,
perhaps obtained by reading from a pipe or socket.
This operation is only available
if the kernel is configured with CONFIG_SECCOMP enabled.
With
.IR arg2
set to
.BR SECCOMP_MODE_FILTER " (since Linux 3.5)"
the system calls allowed are
defined by a pointer passed in
.IR arg3
to a Berkeley Packet Filter, which can be designed to filter
arbitrary syscalls and syscall arguments.
This mode is only available if the kernel is configured with
CONFIG_SECCOMP_FILTER enabled.
.TP
.BR PR_GET_SECCOMP " (since Linux 2.6.23)"
Return the secure computing mode of the calling thread.
Not very useful for the current implementation (mode equals 1),
but may be useful for other possible future modes:
if the caller is not in secure computing mode, this operation returns 0;
if the caller is in secure computing mode, then the
If the caller is not in secure computing mode, this operation returns 0;
if the caller is in strict secure computing mode, then the
.BR prctl ()
call will cause a
.B SIGKILL
signal to be sent to the process.
If the caller is in filter mode, and this syscall is allowed by the
seccomp filters, it returns 2.
This operation is only available
if the kernel is configured with CONFIG_SECCOMP enabled.
.TP