seccomp: add elevateprivileges argument to command line

This patch introduces the new argument
[,elevateprivileges=allow|deny|children] to the `-sandbox on'. It allows
or denies Qemu process to elevate its privileges by blacklisting all
set*uid|gid system calls. The 'children' option will let forks and
execves run unprivileged.

Signed-off-by: Eduardo Otubo <otubo@redhat.com>
diff --git a/qemu-options.hx b/qemu-options.hx
index 72150c6..5c1b163 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4017,20 +4017,26 @@
 ETEXI
 
 DEF("sandbox", HAS_ARG, QEMU_OPTION_sandbox, \
-    "-sandbox on[,obsolete=allow|deny]\n" \
+    "-sandbox on[,obsolete=allow|deny][,elevateprivileges=allow|deny|children]\n" \
     "                Enable seccomp mode 2 system call filter (default 'off').\n" \
     "                use 'obsolete' to allow obsolete system calls that are provided\n" \
     "                    by the kernel, but typically no longer used by modern\n" \
-    "                    C library implementations.\n",
+    "                    C library implementations.\n" \
+    "                use 'elevateprivileges' to allow or deny QEMU process to elevate\n" \
+    "                    its privileges by blacklisting all set*uid|gid system calls.\n" \
+    "                    The value 'children' will deny set*uid|gid system calls for\n" \
+    "                    main QEMU process but will allow forks and execves to run unprivileged\n",
     QEMU_ARCH_ALL)
 STEXI
-@item -sandbox @var{arg}[,obsolete=@var{string}]
+@item -sandbox @var{arg}[,obsolete=@var{string}][,elevateprivileges=@var{string}]
 @findex -sandbox
 Enable Seccomp mode 2 system call filter. 'on' will enable syscall filtering and 'off' will
 disable it.  The default is 'off'.
 @table @option
 @item obsolete=@var{string}
 Enable Obsolete system calls
+@item elevateprivileges=@var{string}
+Disable set*uid|gid system calls
 @end table
 ETEXI