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gcc-plugins: randstruct: Only warn about true flexible arrays

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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 df8fc4e934 ("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: df8fc4e934 ("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>
This commit is contained in:
Kees Cook 2023-11-04 13:43:37 -07:00
parent 65120498aa
commit 1ee60356c2
1 changed files with 0 additions and 10 deletions
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10
scripts/gcc-plugins/randomize_layout_plugin.c
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@ -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;
}