From: Kristen Carlson Accardi <kristen@linux.intel.com>
To: keescook@chromium.org, tglx@linutronix.de, mingo@redhat.com,
bp@alien8.de
Cc: arjan@linux.intel.com, x86@kernel.org,
linux-kernel@vger.kernel.org,
kernel-hardening@lists.openwall.com, rick.p.edgecombe@intel.com,
Kristen Carlson Accardi <kristen@linux.intel.com>,
Tony Luck <tony.luck@intel.com>
Subject: [PATCH v4 09/10] kallsyms: Hide layout
Date: Fri, 17 Jul 2020 10:00:06 -0700 [thread overview]
Message-ID: <20200717170008.5949-10-kristen@linux.intel.com> (raw)
In-Reply-To: <20200717170008.5949-1-kristen@linux.intel.com>
This patch makes /proc/kallsyms display in a random order, rather
than sorted by address in order to hide the newly randomized address
layout.
Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Tested-by: Tony Luck <tony.luck@intel.com>
---
kernel/kallsyms.c | 163 +++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 162 insertions(+), 1 deletion(-)
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index bb14e64f62a4..45d147f7f10e 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -446,6 +446,12 @@ struct kallsym_iter {
int show_value;
};
+struct kallsyms_shuffled_iter {
+ struct kallsym_iter iter;
+ loff_t total_syms;
+ loff_t shuffled_index[];
+};
+
int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
char *type, char *name)
{
@@ -661,7 +667,7 @@ bool kallsyms_show_value(const struct cred *cred)
}
}
-static int kallsyms_open(struct inode *inode, struct file *file)
+static int __kallsyms_open(struct inode *inode, struct file *file)
{
/*
* We keep iterator in m->private, since normal case is to
@@ -682,6 +688,161 @@ static int kallsyms_open(struct inode *inode, struct file *file)
return 0;
}
+/*
+ * When function granular kaslr is enabled, we need to print out the symbols
+ * at random so we don't reveal the new layout.
+ */
+#if defined(CONFIG_FG_KASLR)
+static int update_random_pos(struct kallsyms_shuffled_iter *s_iter,
+ loff_t pos, loff_t *new_pos)
+{
+ loff_t new;
+
+ if (pos >= s_iter->total_syms)
+ return 0;
+
+ new = s_iter->shuffled_index[pos];
+
+ /*
+ * normally this would be done as part of update_iter, however,
+ * we want to avoid triggering this in the event that new is
+ * zero since we don't want to blow away our pos end indicators.
+ */
+ if (new == 0) {
+ s_iter->iter.name[0] = '\0';
+ s_iter->iter.nameoff = get_symbol_offset(new);
+ s_iter->iter.pos = new;
+ }
+
+ *new_pos = new;
+ return 1;
+}
+
+static void *shuffled_start(struct seq_file *m, loff_t *pos)
+{
+ struct kallsyms_shuffled_iter *s_iter = m->private;
+ loff_t new_pos;
+
+ if (!update_random_pos(s_iter, *pos, &new_pos))
+ return NULL;
+
+ return s_start(m, &new_pos);
+}
+
+static void *shuffled_next(struct seq_file *m, void *p, loff_t *pos)
+{
+ struct kallsyms_shuffled_iter *s_iter = m->private;
+ loff_t new_pos;
+
+ (*pos)++;
+
+ if (!update_random_pos(s_iter, *pos, &new_pos))
+ return NULL;
+
+ if (!update_iter(m->private, new_pos))
+ return NULL;
+
+ return p;
+}
+
+/*
+ * shuffle_index_list()
+ * Use a Fisher Yates algorithm to shuffle a list of text sections.
+ */
+static void shuffle_index_list(loff_t *indexes, loff_t size)
+{
+ int i;
+ unsigned int j;
+ loff_t temp;
+
+ for (i = size - 1; i > 0; i--) {
+ /* pick a random index from 0 to i */
+ get_random_bytes(&j, sizeof(j));
+ j = j % (i + 1);
+
+ temp = indexes[i];
+ indexes[i] = indexes[j];
+ indexes[j] = temp;
+ }
+}
+
+static const struct seq_operations kallsyms_shuffled_op = {
+ .start = shuffled_start,
+ .next = shuffled_next,
+ .stop = s_stop,
+ .show = s_show
+};
+
+static int kallsyms_random_open(struct inode *inode, struct file *file)
+{
+ loff_t pos;
+ struct kallsyms_shuffled_iter *shuffled_iter;
+ struct kallsym_iter iter;
+ bool show_value;
+
+ /*
+ * If privileged, go ahead and use the normal algorithm for
+ * displaying symbols
+ */
+ show_value = kallsyms_show_value(file->f_cred);
+ if (show_value)
+ return __kallsyms_open(inode, file);
+
+ /*
+ * we need to figure out how many extra symbols there are
+ * to print out past kallsyms_num_syms
+ */
+ pos = kallsyms_num_syms;
+ reset_iter(&iter, 0);
+ do {
+ if (!update_iter(&iter, pos))
+ break;
+ pos++;
+ } while (1);
+
+ /*
+ * add storage space for an array of loff_t equal to the size
+ * of the total number of symbols we need to print
+ */
+ shuffled_iter = __seq_open_private(file, &kallsyms_shuffled_op,
+ sizeof(*shuffled_iter) +
+ (sizeof(pos) * pos));
+ if (!shuffled_iter)
+ return -ENOMEM;
+
+ reset_iter(&shuffled_iter->iter, 0);
+ shuffled_iter->iter.show_value = show_value;
+ shuffled_iter->total_syms = pos;
+
+ /*
+ * the existing update_iter algorithm requires that we
+ * are either moving along increasing pos sequentially,
+ * or that these values are correct. Since these values
+ * were discovered above, initialize our new iter so we
+ * can use update_iter non-sequentially.
+ */
+ shuffled_iter->iter.pos_arch_end = iter.pos_arch_end;
+ shuffled_iter->iter.pos_mod_end = iter.pos_mod_end;
+ shuffled_iter->iter.pos_ftrace_mod_end = iter.pos_ftrace_mod_end;
+
+ /*
+ * initialize the array with all possible pos values, then
+ * shuffle the array so that the values will display in a random
+ * order.
+ */
+ for (pos = 0; pos < shuffled_iter->total_syms; pos++)
+ shuffled_iter->shuffled_index[pos] = pos;
+
+ shuffle_index_list(shuffled_iter->shuffled_index, shuffled_iter->total_syms);
+
+ return 0;
+}
+
+#define kallsyms_open kallsyms_random_open
+#else
+#define kallsyms_open __kallsyms_open
+#endif /* CONFIG_FG_KASLR */
+
#ifdef CONFIG_KGDB_KDB
const char *kdb_walk_kallsyms(loff_t *pos)
{
--
2.20.1
next prev parent reply other threads:[~2020-07-17 17:02 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-17 16:59 [PATCH v4 00/10] Function Granular KASLR Kristen Carlson Accardi
2020-07-17 16:59 ` [PATCH v4 01/10] objtool: Do not assume order of parent/child functions Kristen Carlson Accardi
2020-07-17 16:59 ` [PATCH v4 02/10] x86: tools/relocs: Support >64K section headers Kristen Carlson Accardi
2020-07-17 17:00 ` [PATCH v4 03/10] x86/boot: Allow a "silent" kaslr random byte fetch Kristen Carlson Accardi
2020-07-17 17:00 ` [PATCH v4 04/10] x86: Makefile: Add build and config option for CONFIG_FG_KASLR Kristen Carlson Accardi
2020-07-17 17:00 ` [PATCH v4 05/10] x86: Make sure _etext includes function sections Kristen Carlson Accardi
2020-07-17 17:00 ` [PATCH v4 06/10] x86/tools: Add relative relocs for randomized functions Kristen Carlson Accardi
2020-07-17 17:00 ` [PATCH v4 07/10] x86/boot/compressed: Avoid duplicate malloc() implementations Kristen Carlson Accardi
2020-07-17 17:00 ` [PATCH v4 08/10] x86: Add support for function granular KASLR Kristen Carlson Accardi
2020-07-17 17:00 ` Kristen Carlson Accardi [this message]
2020-07-20 1:25 ` [PATCH v4 09/10] kallsyms: Hide layout Kees Cook
2020-07-20 16:59 ` Kristen Carlson Accardi
2020-07-17 17:00 ` [PATCH v4 10/10] module: Reorder functions Kristen Carlson Accardi
2020-07-28 17:29 ` Jessica Yu
2020-07-22 9:27 ` [PATCH v4 00/10] Function Granular KASLR Miroslav Benes
2020-07-22 14:39 ` Kees Cook
2020-07-22 14:51 ` Joe Lawrence
2020-07-22 14:56 ` Joe Lawrence
2020-07-22 18:24 ` Kristen Carlson Accardi
2020-07-22 16:07 ` Josh Poimboeuf
2020-07-22 19:42 ` Kees Cook
2020-07-22 19:56 ` Kristen Carlson Accardi
2020-07-22 21:33 ` Josh Poimboeuf
2020-08-21 23:02 ` Kristen Carlson Accardi
2020-08-25 16:16 ` Joe Lawrence
2020-08-28 10:21 ` Miroslav Benes
2020-08-28 19:24 ` Josh Poimboeuf
2021-01-23 22:59 ` Fangrui Song
2021-01-25 17:21 ` Josh Poimboeuf
2020-08-03 11:39 ` Evgenii Shatokhin
2020-08-03 17:45 ` Kees Cook
2020-08-03 18:17 ` Joe Lawrence
2020-08-03 19:38 ` Frank Ch. Eigler
2020-08-03 20:11 ` Kees Cook
2020-08-03 21:12 ` Frank Ch. Eigler
2020-08-03 21:41 ` Kees Cook
2020-08-04 0:48 ` Frank Ch. Eigler
2020-08-04 17:04 ` Jessica Yu
2020-08-04 18:23 ` Joe Lawrence
2020-08-07 16:38 ` Kristen Carlson Accardi
2020-08-07 17:20 ` Kees Cook
2020-08-10 16:10 ` Kristen Carlson Accardi
2020-08-12 17:18 ` Kristen Carlson Accardi
2020-08-06 15:32 ` Ingo Molnar
2020-08-06 19:24 ` Kristen Carlson Accardi
2020-08-06 19:27 ` Kees Cook
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