linux-kernel - [PATCH] gcc-plugins: randstruct: Remove cast exception handling

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Date:   Tue, 10 May 2022 17:04:56 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Kees Cook <keescook@...omium.org>, linux-hardening@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] gcc-plugins: randstruct: Remove cast exception handling

With all randstruct exceptions removed, remove all the exception
handling code. Any future warnings are likely to be shared between
this plugin and Clang randstruct, and will need to be addressed in a
more wholistic fashion.

Cc: Christoph Hellwig <hch@...radead.org>
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
This depends on the other patches that remove the exception entries:
https://lore.kernel.org/linux-hardening/20220510235817.3627784-1-keescook@chromium.org/
https://lore.kernel.org/linux-hardening/20220510205729.3574400-1-keescook@chromium.org/
https://lore.kernel.org/linux-hardening/20220511000109.3628404-1-keescook@chromium.org/
---
 scripts/gcc-plugins/randomize_layout_plugin.c | 79 +------------------
 1 file changed, 3 insertions(+), 76 deletions(-)

diff --git a/scripts/gcc-plugins/randomize_layout_plugin.c b/scripts/gcc-plugins/randomize_layout_plugin.c
index 2ca768d88a68..ea2aea570404 100644
--- a/scripts/gcc-plugins/randomize_layout_plugin.c
+++ b/scripts/gcc-plugins/randomize_layout_plugin.c
@@ -39,16 +39,6 @@ static struct plugin_info randomize_layout_plugin_info = {
 			  "performance-mode\tenable cacheline-aware layout randomization\n"
 };
 
-struct whitelist_entry {
-	const char *pathname;
-	const char *lhs;
-	const char *rhs;
-};
-
-static const struct whitelist_entry whitelist[] = {
-	{ }
-};
-
 /* from old Linux dcache.h */
 static inline unsigned long
 partial_name_hash(unsigned long c, unsigned long prevhash)
@@ -734,60 +724,6 @@ static void handle_local_var_initializers(void)
 	}
 }
 
-static bool type_name_eq(gimple stmt, const_tree type_tree, const char *wanted_name)
-{
-	const char *type_name;
-
-	if (type_tree == NULL_TREE)
-		return false;
-
-	switch (TREE_CODE(type_tree)) {
-	case RECORD_TYPE:
-		type_name = TYPE_NAME_POINTER(type_tree);
-		break;
-	case INTEGER_TYPE:
-		if (TYPE_PRECISION(type_tree) == CHAR_TYPE_SIZE)
-			type_name = "char";
-		else {
-			INFORM(gimple_location(stmt), "found non-char INTEGER_TYPE cast comparison: %qT\n", type_tree);
-			debug_tree(type_tree);
-			return false;
-		}
-		break;
-	case POINTER_TYPE:
-		if (TREE_CODE(TREE_TYPE(type_tree)) == VOID_TYPE) {
-			type_name = "void *";
-			break;
-		} else {
-			INFORM(gimple_location(stmt), "found non-void POINTER_TYPE cast comparison %qT\n", type_tree);
-			debug_tree(type_tree);
-			return false;
-		}
-	default:
-		INFORM(gimple_location(stmt), "unhandled cast comparison: %qT\n", type_tree);
-		debug_tree(type_tree);
-		return false;
-	}
-
-	return strcmp(type_name, wanted_name) == 0;
-}
-
-static bool whitelisted_cast(gimple stmt, const_tree lhs_tree, const_tree rhs_tree)
-{
-	const struct whitelist_entry *entry;
-	expanded_location xloc = expand_location(gimple_location(stmt));
-
-	for (entry = whitelist; entry->pathname; entry++) {
-		if (!strstr(xloc.file, entry->pathname))
-			continue;
-
-		if (type_name_eq(stmt, lhs_tree, entry->lhs) && type_name_eq(stmt, rhs_tree, entry->rhs))
-			return true;
-	}
-
-	return false;
-}
-
 /*
  * iterate over all statements to find "bad" casts:
  * those where the address of the start of a structure is cast
@@ -864,10 +800,7 @@ static unsigned int find_bad_casts_execute(void)
 #ifndef __DEBUG_PLUGIN
 				if (lookup_attribute("randomize_performed", TYPE_ATTRIBUTES(ptr_lhs_type)))
 #endif
-				{
-					if (!whitelisted_cast(stmt, ptr_lhs_type, ptr_rhs_type))
-						MISMATCH(gimple_location(stmt), "rhs", ptr_lhs_type, ptr_rhs_type);
-				}
+				MISMATCH(gimple_location(stmt), "rhs", ptr_lhs_type, ptr_rhs_type);
 				continue;
 			}
 
@@ -890,10 +823,7 @@ static unsigned int find_bad_casts_execute(void)
 #ifndef __DEBUG_PLUGIN
 				if (lookup_attribute("randomize_performed", TYPE_ATTRIBUTES(op0_type)))
 #endif
-				{
-					if (!whitelisted_cast(stmt, ptr_lhs_type, op0_type))
-						MISMATCH(gimple_location(stmt), "op0", ptr_lhs_type, op0_type);
-				}
+				MISMATCH(gimple_location(stmt), "op0", ptr_lhs_type, op0_type);
 			} else {
 				const_tree ssa_name_var = SSA_NAME_VAR(rhs1);
 				/* skip bogus type casts introduced by container_of */
@@ -903,10 +833,7 @@ static unsigned int find_bad_casts_execute(void)
 #ifndef __DEBUG_PLUGIN
 				if (lookup_attribute("randomize_performed", TYPE_ATTRIBUTES(ptr_rhs_type)))
 #endif
-				{
-					if (!whitelisted_cast(stmt, ptr_lhs_type, ptr_rhs_type))
-						MISMATCH(gimple_location(stmt), "ssa", ptr_lhs_type, ptr_rhs_type);
-				}
+				MISMATCH(gimple_location(stmt), "ssa", ptr_lhs_type, ptr_rhs_type);
 			}
 
 		}
-- 
2.32.0