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Commit 6933bc9a authored by Kees Cook's avatar Kees Cook Committed by Greg Kroah-Hartman
Browse files

randstruct: Fix gcc-plugin performance mode to stay in group 



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: default avatarLukas Loidolt <e1634039@student.tuwien.ac.at>
Closes: https://lore.kernel.org/all/f3ca77f0-e414-4065-83a5-ae4c4d25545d@student.tuwien.ac.at


Fixes: 313dd1b6 ("gcc-plugins: Add the randstruct plugin")
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent c94d05ac

scripts/gcc-plugins/randomize_layout_plugin.c

+8 −3
Original line number Diff line number Diff line
@@ -209,12 +209,14 @@ static void partition_struct(tree *fields, unsigned long length, struct partitio 


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);
@@ -224,11 +226,14 @@ static void performance_shuffle(tree *newtree, unsigned long length, ranctx *prn 
	}



	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;