Add C define to remove taint support from perl

By defining NO_TAINT_SUPPORT, all the various checks that perl does for
tainting become no-ops. It's not an entirely complete change: it doesn't
attempt to remove the taint-related interpreter variables, but instead
virtually eliminates access to it.

Why, you ask? Because it appears to speed up perl's run-time
significantly by avoiding various "are we running under taint" checks
and the like.

This change is not in a state to go into blead yet. The actual way I
implemented it might raise some (valid) objections. Basically, I
replaced all uses of the global taint variables (but not PL_taint_warn!)
with an extra layer of get/set macros (TAINT_get/TAINTING_get).
Furthermore, the change is not complete:

- PL_taint_warn would likely deserve the same treatment.
- Obviously, tests fail. We have tests for -t/-T
- Right now, I added a Perl warn() on startup when -t/-T are detected
  but the perl was not compiled support it. It might be argued that it
  should be silently ignored! Needs some thinking.
- Code quality concerns - needs review.
- Configure support required.
- Needs thinking: How does this tie in with CPAN XS modules that use
  PL_taint and friends? It's easy to backport the new macros via PPPort,
  but that doesn't magically change all code out there. Might be
  harmless, though, because whenever you're running under
  NO_TAINT_SUPPORT, any check of PL_taint/etc is going to come up false.
  Thus, the only CPAN code that SHOULD be adversely affected is code
  that changes taint state.

1 files changed, 45 insertions, 5 deletions

diff --git a/perl.h b/perl.h
index ae84dba59b..f187ebac60 100644
--- a/perl.h
+++ b/perl.h
@@ -528,11 +528,51 @@ register struct op *Perl_op asm(stringify(OP_IN_REGISTER));
 #   define VOL
 #endif
 
-#define TAINT		(PL_tainted = TRUE)
-#define TAINT_NOT	(PL_tainted = FALSE)
-#define TAINT_IF(c)	if (c) { PL_tainted = TRUE; }
-#define TAINT_ENV()	if (PL_tainting) { taint_env(); }
-#define TAINT_PROPER(s)	if (PL_tainting) { taint_proper(NULL, s); }
+/* By compiling a perl with -DNO_TAINT_SUPPORT or -DSILENT_NO_TAINT_SUPPORT,
+ * you get a perl without taint support, but doubtlessly with a lesser
+ * degree of support. Do not do so unless you know exactly what it means
+ * technically, have a good reason to do so, and know exactly how the
+ * perl will be used. perls with -DSILENT_NO_TAINT_SUPPORT are considered
+ * a potential security risk due to flat out ignoring the security-relevant
+ * taint flags. This being said, a perl without taint support compiled in
+ * has marginal run-time performance benefits.
+ * SILENT_NO_TAINT_SUPPORT implies NO_TAINT_SUPPORT.
+ * SILENT_NO_TAINT_SUPPORT is the same as NO_TAINT_SUPPORT except it
+ * silently ignores -t/-T instead of throwing an exception.
+ */
+#if SILENT_NO_TAINT_SUPPORT && !defined(NO_TAINT_SUPPORT)
+#  define NO_TAINT_SUPPORT 1
+#endif
+
+/* NO_TAINT_SUPPORT can be set to transform virtually all taint-related
+ * operations into no-ops for a very modest speed-up. Enable only if you
+ * know what you're doing: tests and CPAN modules' tests are bound to fail.
+ */
+#if NO_TAINT_SUPPORT
+#   define TAINT		NOOP
+#   define TAINT_NOT		NOOP
+#   define TAINT_IF(c)		NOOP
+#   define TAINT_ENV()		NOOP
+#   define TAINT_PROPER(s)	NOOP
+#   define TAINT_set(s)		NOOP
+#   define TAINT_get		0
+#   define TAINTING_get		0
+#   define TAINTING_set(s)	NOOP
+#   define TAINT_WARN_get       0
+#   define TAINT_WARN_set(s)    NOOP
+#else
+#   define TAINT		(PL_tainted = TRUE)
+#   define TAINT_NOT	(PL_tainted = FALSE)
+#   define TAINT_IF(c)	if (c) { PL_tainted = TRUE; }
+#   define TAINT_ENV()	if (PL_tainting) { taint_env(); }
+#   define TAINT_PROPER(s)	if (PL_tainting) { taint_proper(NULL, s); }
+#   define TAINT_set(s)		(PL_tainted = (s))
+#   define TAINT_get		(PL_tainted)
+#   define TAINTING_get		(PL_tainting)
+#   define TAINTING_set(s)	(PL_tainting = (s))
+#   define TAINT_WARN_get       (PL_taint_warn)
+#   define TAINT_WARN_set(s)    (PL_taint_warn = (s))
+#endif
 
 /* flags used internally only within pp_subst and pp_substcont */
 #ifdef PERL_CORE