From 1ee60356c2dca938362528404af95b8ef3e49b6a Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Sat, 4 Nov 2023 13:43:37 -0700 Subject: gcc-plugins: randstruct: Only warn about true flexible arrays 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 Cc: linux-hardening@vger.kernel.org Reported-by: kernel test robot 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 Acked-by: "Gustavo A. R. Silva" Link: https://lore.kernel.org/r/20231104204334.work.160-kees@kernel.org Signed-off-by: Kees Cook --- scripts/gcc-plugins/randomize_layout_plugin.c | 10 ---------- 1 file changed, 10 deletions(-) (limited to 'scripts/gcc-plugins/randomize_layout_plugin.c') diff --git a/scripts/gcc-plugins/randomize_layout_plugin.c b/scripts/gcc-plugins/randomize_layout_plugin.c index 366395cab490..910bd21d08f4 100644 --- a/scripts/gcc-plugins/randomize_layout_plugin.c +++ b/scripts/gcc-plugins/randomize_layout_plugin.c @@ -278,8 +278,6 @@ 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); @@ -287,20 +285,12 @@ 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; } -- cgit v1.2.3 From d71f22365a9caca82d424f3a33445de46567e198 Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Sat, 25 Nov 2023 15:49:12 -0600 Subject: gcc-plugins: randstruct: Update code comment in relayout_struct() Update code comment to clarify that the only element whose layout is not randomized is a proper C99 flexible-array member. This update is complementary to commit 1ee60356c2dc ("gcc-plugins: randstruct: Only warn about true flexible arrays") Signed-off-by: "Gustavo A. R. Silva" Link: https://lore.kernel.org/r/ZWJr2MWDjXLHE8ap@work Fixes: 1ee60356c2dc ("gcc-plugins: randstruct: Only warn about true flexible arrays") Signed-off-by: Kees Cook --- scripts/gcc-plugins/randomize_layout_plugin.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'scripts/gcc-plugins/randomize_layout_plugin.c') diff --git a/scripts/gcc-plugins/randomize_layout_plugin.c b/scripts/gcc-plugins/randomize_layout_plugin.c index 910bd21d08f4..746ff2d272f2 100644 --- a/scripts/gcc-plugins/randomize_layout_plugin.c +++ b/scripts/gcc-plugins/randomize_layout_plugin.c @@ -339,8 +339,7 @@ static int relayout_struct(tree type) /* * enforce that we don't randomize the layout of the last - * element of a struct if it's a 0 or 1-length array - * or a proper flexible array + * element of a struct if it's a proper flexible array */ if (is_flexible_array(newtree[num_fields - 1])) { has_flexarray = true; -- cgit v1.2.3