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Message-Id: <20231008170552.work.766-kees@kernel.org> Date: Sun, 8 Oct 2023 10:05:56 -0700 From: Kees Cook <keescook@...omium.org> To: linux-hardening@...r.kernel.org Cc: Kees Cook <keescook@...omium.org>, Lukas Loidolt <e1634039@...dent.tuwien.ac.at>, linux-kernel@...r.kernel.org Subject: [PATCH] randstruct: Fix gcc-plugin performance mode to stay in group 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@...r.kernel.org Reported-by: Lukas Loidolt <e1634039@...dent.tuwien.ac.at> Closes: https://lore.kernel.org/all/f3ca77f0-e414-4065-83a5-ae4c4d25545d@student.tuwien.ac.at Signed-off-by: Kees Cook <keescook@...omium.org> --- scripts/gcc-plugins/randomize_layout_plugin.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/scripts/gcc-plugins/randomize_layout_plugin.c b/scripts/gcc-plugins/randomize_layout_plugin.c index 951b74ba1b24..366395cab490 100644 --- 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 *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); @@ -206,11 +208,14 @@ 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; -- 2.34.1
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