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putty-source/windows/plink.c
Simon Tatham 98200d1bfe Arm: turn on PSTATE.DIT if available and needed. 
DIT, for 'Data-Independent Timing', is a bit you can set in the
processor state on sufficiently new Arm CPUs, which promises that a
long list of instructions will deliberately avoid varying their timing
based on the input register values. Just what you want for keeping
your constant-time crypto primitives constant-time.

As far as I'm aware, no CPU has _yet_ implemented any data-dependent
optimisations, so DIT is a safety precaution against them doing so in
future. It would be embarrassing to be caught without it if a future
CPU does do that, so we now turn on DIT in the PuTTY process state.

I've put a call to the new enable_dit() function at the start of every
main() and WinMain() belonging to a program that might do
cryptography (even testcrypt, in case someone uses it for something!),
and in case I missed one there, also added a second call at the first
moment that any cryptography-using part of the code looks as if it
might become active: when an instance of the SSH protocol object is
configured, when the system PRNG is initialised, and when selecting
any cryptographic authentication protocol in an HTTP or SOCKS proxy
connection. With any luck those precautions between them should ensure
it's on whenever we need it.

Arm's own recommendation is that you should carefully choose the
granularity at which you enable and disable DIT: there's a potential
time cost to turning it on and off (I'm not sure what, but plausibly
something of the order of a pipeline flush), so it's a performance hit
to do it _inside_ each individual crypto function, but if CPUs start
supporting significant data-dependent optimisation in future, then it
will also become a noticeable performance hit to just leave it on
across the whole process. So you'd like to do it somewhere in the
middle: for example, you might turn on DIT once around the whole
process of verifying and decrypting an SSH packet, instead of once for
decryption and once for MAC.

With all respect to that recommendation as a strategy for maximum
performance, I'm not following it here. I turn on DIT at the start of
the PuTTY process, and then leave it on. Rationale:

 1. PuTTY is not otherwise a performance-critical application: it's
    not likely to max out your CPU for any purpose _other_ than
    cryptography. The most CPU-intensive non-cryptographic thing I can
    imagine a PuTTY process doing is the complicated computation of
    font rendering in the terminal, and that will normally be cached
    (you don't recompute each glyph from its outline and hints for
    every time you display it).

 2. I think a bigger risk lies in accidental side channels from having
    DIT turned off when it should have been on. I can imagine lots of
    causes for that. Missing a crypto operation in some unswept corner
    of the code; confusing control flow (like my coroutine macros)
    jumping with DIT clear into the middle of a region of code that
    expected DIT to have been set at the beginning; having a reference
    counter of DIT requests and getting it out of sync.

In a more sophisticated programming language, it might be possible to
avoid the risk in #2 by cleverness with the type system. For example,
in Rust, you could have a zero-sized type that acts as a proof token
for DIT being enabled (it would be constructed by a function that also
sets DIT, have a Drop implementation that clears DIT, and be !Send so
you couldn't use it in a thread other than the one where DIT was set),
and then you could require all the actual crypto functions to take a
DitToken as an extra parameter, at zero runtime cost. Then "oops I
forgot to set DIT around this piece of crypto" would become a compile
error. Even so, you'd have to take some care with coroutine-structured
code (what happens if a Rust async function yields while holding a DIT
token?) and with nesting (if you have two DIT tokens, you don't want
dropping the inner one to clear DIT while the outer one is still there
to wrongly convince callees that it's set). Maybe in Rust you could
get this all to work reliably. But not in C!

DIT is an optional feature of the Arm architecture, so we must first
test to see if it's supported. This is done the same way as we already
do for the various Arm crypto accelerators: on ELF-based systems,
check the appropriate bit in the 'hwcap' words in the ELF aux vector;
on Mac, look for an appropriate sysctl flag.

On Windows I don't know of a way to query the DIT feature, _or_ of a
way to write the necessary enabling instruction in an MSVC-compatible
way. I've _heard_ that it might not be necessary, because Windows
might just turn on DIT unconditionally and leave it on, in an even
more extreme version of my own strategy. I don't have a source for
that - I heard it by word of mouth - but I _hope_ it's true, because
that would suit me very well! Certainly I can't write code to enable
DIT without knowing (a) how to do it, (b) how to know if it's safe.
Nonetheless, I've put the enable_dit() call in all the right places in
the Windows main programs as well as the Unix and cross-platform code,
so that if I later find out that I _can_ put in an explicit enable of
DIT in some way, I'll only have to arrange to set HAVE_ARM_DIT and
compile the enable_dit() function appropriately.
2024-12-19 08:52:47 +00:00

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/*
* PLink - a Windows command-line (stdin/stdout) variant of PuTTY.
*/
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <stdarg.h>
#include "putty.h"
#include "ssh.h"
#include "storage.h"
#include "tree234.h"
#include "security-api.h"
void cmdline_error(const char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
console_print_error_msg_fmt_v("plink", fmt, ap);
va_end(ap);
exit(1);
}
static HANDLE inhandle, outhandle, errhandle;
static struct handle *stdin_handle, *stdout_handle, *stderr_handle;
static handle_sink stdout_hs, stderr_hs;
static StripCtrlChars *stdout_scc, *stderr_scc;
static BinarySink *stdout_bs, *stderr_bs;
static DWORD orig_console_mode;
static Backend *backend;
static LogContext *logctx;
static Conf *conf;
static void plink_echoedit_update(Seat *seat, bool echo, bool edit)
{
/* Update stdin read mode to reflect changes in line discipline. */
DWORD mode;
mode = ENABLE_PROCESSED_INPUT;
if (echo)
mode = mode | ENABLE_ECHO_INPUT;
else
mode = mode & ~ENABLE_ECHO_INPUT;
if (edit)
mode = mode | ENABLE_LINE_INPUT;
else
mode = mode & ~ENABLE_LINE_INPUT;
SetConsoleMode(inhandle, mode);
}
static size_t plink_output(
Seat *seat, SeatOutputType type, const void *data, size_t len)
{
bool is_stderr = type != SEAT_OUTPUT_STDOUT;
BinarySink *bs = is_stderr ? stderr_bs : stdout_bs;
put_data(bs, data, len);
return handle_backlog(stdout_handle) + handle_backlog(stderr_handle);
}
static bool plink_eof(Seat *seat)
{
handle_write_eof(stdout_handle);
return false; /* do not respond to incoming EOF with outgoing */
}
static SeatPromptResult plink_get_userpass_input(Seat *seat, prompts_t *p)
{
/* Plink doesn't support Restart Session, so we can just have a
* single static cmdline_get_passwd_input_state that's never reset */
static cmdline_get_passwd_input_state cmdline_state =
CMDLINE_GET_PASSWD_INPUT_STATE_INIT;
SeatPromptResult spr;
spr = cmdline_get_passwd_input(p, &cmdline_state, false);
if (spr.kind == SPRK_INCOMPLETE)
spr = console_get_userpass_input(p);
return spr;
}
static bool plink_seat_interactive(Seat *seat)
{
return (!*conf_get_str_ambi(conf, CONF_remote_cmd, NULL) &&
!*conf_get_str_ambi(conf, CONF_remote_cmd2, NULL) &&
!*conf_get_str(conf, CONF_ssh_nc_host));
}
static const SeatVtable plink_seat_vt = {
.output = plink_output,
.eof = plink_eof,
.sent = nullseat_sent,
.banner = nullseat_banner_to_stderr,
.get_userpass_input = plink_get_userpass_input,
.notify_session_started = nullseat_notify_session_started,
.notify_remote_exit = nullseat_notify_remote_exit,
.notify_remote_disconnect = nullseat_notify_remote_disconnect,
.connection_fatal = console_connection_fatal,
.nonfatal = console_nonfatal,
.update_specials_menu = nullseat_update_specials_menu,
.get_ttymode = nullseat_get_ttymode,
.set_busy_status = nullseat_set_busy_status,
.confirm_ssh_host_key = console_confirm_ssh_host_key,
.confirm_weak_crypto_primitive = console_confirm_weak_crypto_primitive,
.confirm_weak_cached_hostkey = console_confirm_weak_cached_hostkey,
.prompt_descriptions = console_prompt_descriptions,
.is_utf8 = nullseat_is_never_utf8,
.echoedit_update = plink_echoedit_update,
.get_x_display = nullseat_get_x_display,
.get_windowid = nullseat_get_windowid,
.get_window_pixel_size = nullseat_get_window_pixel_size,
.stripctrl_new = console_stripctrl_new,
.set_trust_status = console_set_trust_status,
.can_set_trust_status = console_can_set_trust_status,
.has_mixed_input_stream = console_has_mixed_input_stream,
.verbose = cmdline_seat_verbose,
.interactive = plink_seat_interactive,
.get_cursor_position = nullseat_get_cursor_position,
};
static Seat plink_seat[1] = {{ &plink_seat_vt }};
static DWORD main_thread_id;
/*
* Short description of parameters.
*/
static void usage(void)
{
printf("Plink: command-line connection utility\n");
printf("%s\n", ver);
printf("Usage: plink [options] [user@]host [command]\n");
printf(" (\"host\" can also be a PuTTY saved session name)\n");
printf("Options:\n");
printf(" -V print version information and exit\n");
printf(" -pgpfp print PGP key fingerprints and exit\n");
printf(" -v show verbose messages\n");
printf(" -load sessname Load settings from saved session\n");
printf(" -ssh -telnet -rlogin -raw -serial\n");
printf(" force use of a particular protocol\n");
printf(" -ssh-connection\n");
printf(" force use of the bare ssh-connection protocol\n");
printf(" -P port connect to specified port\n");
printf(" -l user connect with specified username\n");
printf(" -batch disable all interactive prompts\n");
printf(" -proxycmd command\n");
printf(" use 'command' as local proxy\n");
printf(" -sercfg configuration-string (e.g. 19200,8,n,1,X)\n");
printf(" Specify the serial configuration (serial only)\n");
printf("The following options only apply to SSH connections:\n");
printf(" -pwfile file login with password read from specified file\n");
printf(" -D [listen-IP:]listen-port\n");
printf(" Dynamic SOCKS-based port forwarding\n");
printf(" -L [listen-IP:]listen-port:host:port\n");
printf(" Forward local port to remote address\n");
printf(" -R [listen-IP:]listen-port:host:port\n");
printf(" Forward remote port to local address\n");
printf(" -X -x enable / disable X11 forwarding\n");
printf(" -A -a enable / disable agent forwarding\n");
printf(" -t -T enable / disable pty allocation\n");
printf(" -1 -2 force use of particular SSH protocol version\n");
printf(" -4 -6 force use of IPv4 or IPv6\n");
printf(" -C enable compression\n");
printf(" -i key private key file for user authentication\n");
printf(" -noagent disable use of Pageant\n");
printf(" -agent enable use of Pageant\n");
printf(" -no-trivial-auth\n");
printf(" disconnect if SSH authentication succeeds trivially\n");
printf(" -noshare disable use of connection sharing\n");
printf(" -share enable use of connection sharing\n");
printf(" -hostkey keyid\n");
printf(" manually specify a host key (may be repeated)\n");
printf(" -sanitise-stderr, -sanitise-stdout, "
"-no-sanitise-stderr, -no-sanitise-stdout\n");
printf(" do/don't strip control chars from standard "
"output/error\n");
printf(" -no-antispoof omit anti-spoofing prompt after "
"authentication\n");
printf(" -m file read remote command(s) from file\n");
printf(" -s remote command is an SSH subsystem (SSH-2 only)\n");
printf(" -N don't start a shell/command (SSH-2 only)\n");
printf(" -nc host:port\n");
printf(" open tunnel in place of session (SSH-2 only)\n");
printf(" -sshlog file\n");
printf(" -sshrawlog file\n");
printf(" log protocol details to a file\n");
printf(" -logoverwrite\n");
printf(" -logappend\n");
printf(" control what happens when a log file already exists\n");
printf(" -shareexists\n");
printf(" test whether a connection-sharing upstream exists\n");
}
static void version(void)
{
char *buildinfo_text = buildinfo("\n");
printf("plink: %s\n%s\n", ver, buildinfo_text);
sfree(buildinfo_text);
exit(0);
}
size_t stdin_gotdata(struct handle *h, const void *data, size_t len, int err)
{
if (err) {
char buf[4096];
FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, NULL, err, 0,
buf, lenof(buf), NULL);
buf[lenof(buf)-1] = '\0';
if (buf[strlen(buf)-1] == '\n')
buf[strlen(buf)-1] = '\0';
fprintf(stderr, "Unable to read from standard input: %s\n", buf);
cleanup_exit(0);
}
noise_ultralight(NOISE_SOURCE_IOLEN, len);
if (backend_connected(backend)) {
if (len > 0) {
backend_send(backend, data, len);
return backend_sendbuffer(backend);
} else {
backend_special(backend, SS_EOF, 0);
return 0;
}
} else
return 0;
}
void stdouterr_sent(struct handle *h, size_t new_backlog, int err, bool close)
{
if (close) {
CloseHandle(outhandle);
CloseHandle(errhandle);
outhandle = errhandle = INVALID_HANDLE_VALUE;
}
if (err) {
char buf[4096];
FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, NULL, err, 0,
buf, lenof(buf), NULL);
buf[lenof(buf)-1] = '\0';
if (buf[strlen(buf)-1] == '\n')
buf[strlen(buf)-1] = '\0';
fprintf(stderr, "Unable to write to standard %s: %s\n",
(h == stdout_handle ? "output" : "error"), buf);
cleanup_exit(0);
}
if (backend_connected(backend)) {
backend_unthrottle(backend, (handle_backlog(stdout_handle) +
handle_backlog(stderr_handle)));
}
}
const bool share_can_be_downstream = true;
const bool share_can_be_upstream = true;
const unsigned cmdline_tooltype =
TOOLTYPE_HOST_ARG |
TOOLTYPE_HOST_ARG_CAN_BE_SESSION |
TOOLTYPE_HOST_ARG_PROTOCOL_PREFIX |
TOOLTYPE_HOST_ARG_FROM_LAUNCHABLE_LOAD;
static bool sending;
static bool plink_mainloop_pre(void *vctx, const HANDLE **extra_handles,
size_t *n_extra_handles)
{
if (!sending && backend_sendok(backend)) {
stdin_handle = handle_input_new(inhandle, stdin_gotdata, NULL,
0);
sending = true;
}
return true;
}
static bool plink_mainloop_post(void *vctx, size_t extra_handle_index)
{
if (sending)
handle_unthrottle(stdin_handle, backend_sendbuffer(backend));
if (!backend_connected(backend) &&
handle_backlog(stdout_handle) + handle_backlog(stderr_handle) == 0)
return false; /* we closed the connection */
return true;
}
int main(int argc, char **argv)
{
int exitcode;
bool errors;
bool use_subsystem = false;
bool just_test_share_exists = false;
enum TriState sanitise_stdout = AUTO, sanitise_stderr = AUTO;
const struct BackendVtable *vt;
dll_hijacking_protection();
enable_dit();
/*
* Initialise port and protocol to sensible defaults. (These
* will be overridden by more or less anything.)
*/
settings_set_default_protocol(PROT_SSH);
settings_set_default_port(22);
/*
* Process the command line.
*/
conf = conf_new();
do_defaults(NULL, conf);
settings_set_default_protocol(conf_get_int(conf, CONF_protocol));
settings_set_default_port(conf_get_int(conf, CONF_port));
errors = false;
{
/*
* Override the default protocol if PLINK_PROTOCOL is set.
*/
char *p = getenv("PLINK_PROTOCOL");
if (p) {
const struct BackendVtable *vt = backend_vt_from_name(p);
if (vt) {
settings_set_default_protocol(vt->protocol);
settings_set_default_port(vt->default_port);
conf_set_int(conf, CONF_protocol, vt->protocol);
conf_set_int(conf, CONF_port, vt->default_port);
}
}
}
CmdlineArgList *arglist = cmdline_arg_list_from_GetCommandLineW();
size_t arglistpos = 0;
while (arglist->args[arglistpos]) {
CmdlineArg *arg = arglist->args[arglistpos++];
CmdlineArg *nextarg = arglist->args[arglistpos];
const char *p = cmdline_arg_to_str(arg);
int ret = cmdline_process_param(arg, nextarg, 1, conf);
if (ret == -2) {
fprintf(stderr,
"plink: option \"%s\" requires an argument\n", p);
errors = true;
} else if (ret == 2) {
arglistpos++;
} else if (ret == 1) {
continue;
} else if (!strcmp(p, "-s")) {
/* Save status to write to conf later. */
use_subsystem = true;
} else if (!strcmp(p, "-V") || !strcmp(p, "--version")) {
version();
} else if (!strcmp(p, "--help")) {
usage();
exit(0);
} else if (!strcmp(p, "-pgpfp")) {
pgp_fingerprints();
exit(0);
} else if (!strcmp(p, "-shareexists")) {
just_test_share_exists = true;
} else if (!strcmp(p, "-sanitise-stdout") ||
!strcmp(p, "-sanitize-stdout")) {
sanitise_stdout = FORCE_ON;
} else if (!strcmp(p, "-no-sanitise-stdout") ||
!strcmp(p, "-no-sanitize-stdout")) {
sanitise_stdout = FORCE_OFF;
} else if (!strcmp(p, "-sanitise-stderr") ||
!strcmp(p, "-sanitize-stderr")) {
sanitise_stderr = FORCE_ON;
} else if (!strcmp(p, "-no-sanitise-stderr") ||
!strcmp(p, "-no-sanitize-stderr")) {
sanitise_stderr = FORCE_OFF;
} else if (!strcmp(p, "-no-antispoof")) {
console_antispoof_prompt = false;
} else if (*p != '-') {
strbuf *cmdbuf = strbuf_new();
while (arg) {
if (cmdbuf->len > 0)
put_byte(cmdbuf, ' '); /* add space separator */
put_dataz(cmdbuf, cmdline_arg_to_utf8(arg));
arg = arglist->args[arglistpos++];
}
conf_set_str(conf, CONF_remote_cmd, cmdbuf->s);
conf_set_str(conf, CONF_remote_cmd2, "");
conf_set_bool(conf, CONF_nopty, true); /* command => no tty */
strbuf_free(cmdbuf);
break; /* done with cmdline */
} else {
fprintf(stderr, "plink: unknown option \"%s\"\n", p);
errors = true;
}
}
if (errors)
return 1;
if (!cmdline_host_ok(conf)) {
fprintf(stderr, "plink: no valid host name provided\n"
"try \"plink --help\" for help\n");
cmdline_arg_list_free(arglist);
return 1;
}
prepare_session(conf);
/*
* Perform command-line overrides on session configuration.
*/
cmdline_run_saved(conf);
/*
* Apply subsystem status.
*/
if (use_subsystem)
conf_set_bool(conf, CONF_ssh_subsys, true);
/*
* Select protocol. This is farmed out into a table in a
* separate file to enable an ssh-free variant.
*/
vt = backend_vt_from_proto(conf_get_int(conf, CONF_protocol));
if (vt == NULL) {
fprintf(stderr,
"Internal fault: Unsupported protocol found\n");
return 1;
}
if (vt->flags & BACKEND_NEEDS_TERMINAL) {
fprintf(stderr,
"Plink doesn't support %s, which needs terminal emulation\n",
vt->displayname_lc);
return 1;
}
sk_init();
if (p_WSAEventSelect == NULL) {
fprintf(stderr, "Plink requires WinSock 2\n");
return 1;
}
/*
* Plink doesn't provide any way to add forwardings after the
* connection is set up, so if there are none now, we can safely set
* the "simple" flag.
*/
if (conf_get_int(conf, CONF_protocol) == PROT_SSH &&
!conf_get_bool(conf, CONF_x11_forward) &&
!conf_get_bool(conf, CONF_agentfwd) &&
!conf_get_str_nthstrkey(conf, CONF_portfwd, 0))
conf_set_bool(conf, CONF_ssh_simple, true);
logctx = log_init(console_cli_logpolicy, conf);
if (just_test_share_exists) {
if (!vt->test_for_upstream) {
fprintf(stderr, "Connection sharing not supported for this "
"connection type (%s)'\n", vt->displayname_lc);
return 1;
}
if (vt->test_for_upstream(conf_get_str(conf, CONF_host),
conf_get_int(conf, CONF_port), conf))
return 0;
else
return 1;
}
if (restricted_acl()) {
lp_eventlog(console_cli_logpolicy,
"Running with restricted process ACL");
}
inhandle = GetStdHandle(STD_INPUT_HANDLE);
outhandle = GetStdHandle(STD_OUTPUT_HANDLE);
errhandle = GetStdHandle(STD_ERROR_HANDLE);
/*
* Turn off ECHO and LINE input modes. We don't care if this
* call fails, because we know we aren't necessarily running in
* a console.
*/
GetConsoleMode(inhandle, &orig_console_mode);
SetConsoleMode(inhandle, ENABLE_PROCESSED_INPUT);
/*
* Pass the output handles to the handle-handling subsystem.
* (The input one we leave until we're through the
* authentication process.)
*/
stdout_handle = handle_output_new(outhandle, stdouterr_sent, NULL, 0);
stderr_handle = handle_output_new(errhandle, stdouterr_sent, NULL, 0);
handle_sink_init(&stdout_hs, stdout_handle);
handle_sink_init(&stderr_hs, stderr_handle);
stdout_bs = BinarySink_UPCAST(&stdout_hs);
stderr_bs = BinarySink_UPCAST(&stderr_hs);
/*
* Decide whether to sanitise control sequences out of standard
* output and standard error.
*
* If we weren't given a command-line override, we do this if (a)
* the fd in question is pointing at a console, and (b) we aren't
* trying to allocate a terminal as part of the session.
*
* (Rationale: the risk of control sequences is that they cause
* confusion when sent to a local console, so if there isn't one,
* no problem. Also, if we allocate a remote terminal, then we
* sent a terminal type, i.e. we told it what kind of escape
* sequences we _like_, i.e. we were expecting to receive some.)
*/
if (sanitise_stdout == FORCE_ON ||
(sanitise_stdout == AUTO && is_console_handle(outhandle) &&
conf_get_bool(conf, CONF_nopty))) {
stdout_scc = stripctrl_new(stdout_bs, true, L'\0');
stdout_bs = BinarySink_UPCAST(stdout_scc);
}
if (sanitise_stderr == FORCE_ON ||
(sanitise_stderr == AUTO && is_console_handle(errhandle) &&
conf_get_bool(conf, CONF_nopty))) {
stderr_scc = stripctrl_new(stderr_bs, true, L'\0');
stderr_bs = BinarySink_UPCAST(stderr_scc);
}
/*
* Start up the connection.
*/
winselcli_setup(); /* ensure event object exists */
{
char *error, *realhost;
/* nodelay is only useful if stdin is a character device (console) */
bool nodelay = conf_get_bool(conf, CONF_tcp_nodelay) &&
(GetFileType(GetStdHandle(STD_INPUT_HANDLE)) == FILE_TYPE_CHAR);
error = backend_init(vt, plink_seat, &backend, logctx, conf,
conf_get_str(conf, CONF_host),
conf_get_int(conf, CONF_port),
&realhost, nodelay,
conf_get_bool(conf, CONF_tcp_keepalives));
if (error) {
fprintf(stderr, "Unable to open connection:\n%s", error);
sfree(error);
return 1;
}
ldisc_create(conf, NULL, backend, plink_seat);
sfree(realhost);
}
main_thread_id = GetCurrentThreadId();
sending = false;
cli_main_loop(plink_mainloop_pre, plink_mainloop_post, NULL);
exitcode = backend_exitcode(backend);
if (exitcode < 0) {
fprintf(stderr, "Remote process exit code unavailable\n");
exitcode = 1; /* this is an error condition */
}
cleanup_exit(exitcode);
return 0; /* placate compiler warning */
}
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