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Message-ID: <202310062111.809AB4E56@keescook>
Date: Fri, 6 Oct 2023 21:12:06 -0700
From: Kees Cook <keescook@...omium.org>
To: Lukas Loidolt <e1634039@...dent.tuwien.ac.at>
Cc: linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
Daniel Marth <daniel.marth@...o.tuwien.ac.at>
Subject: Re: Missing cache considerations in randstruct performance feature
On Sat, Oct 07, 2023 at 12:30:01AM +0200, Lukas Loidolt wrote:
> In my tests, however, the performance version behaves more or less like the
> full version of randstruct.
Can you try this patch?
commit d73a3244700d3c945cedea7e1fb7042243c41e08
Author: Kees Cook <keescook@...omium.org>
AuthorDate: Fri Oct 6 21:09:28 2023 -0700
Commit: Kees Cook <keescook@...omium.org>
CommitDate: Fri Oct 6 21:09:28 2023 -0700
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>
diff --git a/scripts/gcc-plugins/randomize_layout_plugin.c b/scripts/gcc-plugins/randomize_layout_plugin.c
index 951b74ba1b24..178831917f01 100644
--- a/scripts/gcc-plugins/randomize_layout_plugin.c
+++ b/scripts/gcc-plugins/randomize_layout_plugin.c
@@ -191,7 +191,7 @@ 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;
@@ -206,11 +206,14 @@ 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 += size_group[x].start;
// we could handle this case differently if desired
if (DECL_BIT_FIELD_TYPE(newtree[randnum]))
continue;
--
Kees Cook
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