[PATCH 6.5 170/491] gcc-plugins: randstruct: Only warn about true flexible arrays

[PATCH 6.5 170/491] gcc-plugins: randstruct: Only warn about true flexible arrays

[Greg Kroah-Hartman]

6.5-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kees Cook <keescook@chromium.org>

[ Upstream commit 1ee60356c2dca938362528404af95b8ef3e49b6a ]

The randstruct GCC plugin tried to discover "fake" flexible arrays
to issue warnings about them in randomized structs. In the future
LSM overhead reduction series, it would be legal to have a randomized
struct with a 1-element array, and this should _not_ be treated as a
flexible array, especially since commit df8fc4e934c1 ("kbuild: Enable
-fstrict-flex-arrays=3"). Disable the 0-sized and 1-element array
discovery logic in the plugin, but keep the "true" flexible array check.

Cc: KP Singh <kpsingh@kernel.org>
Cc: linux-hardening@vger.kernel.org
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202311021532.iBwuZUZ0-lkp@intel.com/
Fixes: df8fc4e934c1 ("kbuild: Enable -fstrict-flex-arrays=3")
Reviewed-by: Bill Wendling <morbo@google.com>
Acked-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20231104204334.work.160-kees@kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 scripts/gcc-plugins/randomize_layout_plugin.c | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/scripts/gcc-plugins/randomize_layout_plugin.c b/scripts/gcc-plugins/randomize_layout_plugin.c
index 951b74ba1b242..5e5744b65f8a9 100644
--- a/scripts/gcc-plugins/randomize_layout_plugin.c
+++ b/scripts/gcc-plugins/randomize_layout_plugin.c
@@ -273,8 +273,6 @@ static bool is_flexible_array(const_tree field)
 {
 	const_tree fieldtype;
 	const_tree typesize;
-	const_tree elemtype;
-	const_tree elemsize;
 
 	fieldtype = TREE_TYPE(field);
 	typesize = TYPE_SIZE(fieldtype);
@@ -282,20 +280,12 @@ static bool is_flexible_array(const_tree field)
 	if (TREE_CODE(fieldtype) != ARRAY_TYPE)
 		return false;
 
-	elemtype = TREE_TYPE(fieldtype);
-	elemsize = TYPE_SIZE(elemtype);
-
 	/* size of type is represented in bits */
 
 	if (typesize == NULL_TREE && TYPE_DOMAIN(fieldtype) != NULL_TREE &&
 	    TYPE_MAX_VALUE(TYPE_DOMAIN(fieldtype)) == NULL_TREE)
 		return true;
 
-	if (typesize != NULL_TREE &&
-	    (TREE_CONSTANT(typesize) && (!tree_to_uhwi(typesize) ||
-	     tree_to_uhwi(typesize) == tree_to_uhwi(elemsize))))
-		return true;
-
 	return false;
 }
 
-- 
2.42.0

[PATCH 6.5 230/491] randstruct: Fix gcc-plugin performance mode to stay in group

[Greg Kroah-Hartman]

6.5-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kees Cook <keescook@chromium.org>

commit 381fdb73d1e2a48244de7260550e453d1003bb8e upstream.

The performance mode of the gcc-plugin randstruct was shuffling struct
members outside of the cache-line groups. Limit the range to the
specified group indexes.

Cc: linux-hardening@vger.kernel.org
Cc: stable@vger.kernel.org
Reported-by: Lukas Loidolt <e1634039@student.tuwien.ac.at>
Closes: https://lore.kernel.org/all/f3ca77f0-e414-4065-83a5-ae4c4d25545d@student.tuwien.ac.at
Fixes: 313dd1b62921 ("gcc-plugins: Add the randstruct plugin")
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 scripts/gcc-plugins/randomize_layout_plugin.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- a/scripts/gcc-plugins/randomize_layout_plugin.c
+++ b/scripts/gcc-plugins/randomize_layout_plugin.c
@@ -191,12 +191,14 @@ static void partition_struct(tree *field
 
 static void performance_shuffle(tree *newtree, unsigned long length, ranctx *prng_state)
 {
-	unsigned long i, x;
+	unsigned long i, x, index;
 	struct partition_group size_group[length];
 	unsigned long num_groups = 0;
 	unsigned long randnum;
 
 	partition_struct(newtree, length, (struct partition_group *)&size_group, &num_groups);
+
+	/* FIXME: this group shuffle is currently a no-op. */
 	for (i = num_groups - 1; i > 0; i--) {
 		struct partition_group tmp;
 		randnum = ranval(prng_state) % (i + 1);
@@ -206,11 +208,14 @@ static void performance_shuffle(tree *ne
 	}
 
 	for (x = 0; x < num_groups; x++) {
-		for (i = size_group[x].start + size_group[x].length - 1; i > size_group[x].start; i--) {
+		for (index = size_group[x].length - 1; index > 0; index--) {
 			tree tmp;
+
+			i = size_group[x].start + index;
 			if (DECL_BIT_FIELD_TYPE(newtree[i]))
 				continue;
-			randnum = ranval(prng_state) % (i + 1);
+			randnum = ranval(prng_state) % (index + 1);
+			randnum += size_group[x].start;
 			// we could handle this case differently if desired
 			if (DECL_BIT_FIELD_TYPE(newtree[randnum]))
 				continue;