From:   Alexander Lobakin <alexandr.lobakin@intel.com>
To:     linux-hardening@vger.kernel.org, x86@kernel.org
Cc:     Alexander Lobakin <alexandr.lobakin@intel.com>,
        Jesse Brandeburg <jesse.brandeburg@intel.com>,
        Kristen Carlson Accardi <kristen@linux.intel.com>,
        Kees Cook <keescook@chromium.org>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Ard Biesheuvel <ardb@kernel.org>,
        Tony Luck <tony.luck@intel.com>,
        Bruce Schlobohm <bruce.schlobohm@intel.com>,
        Jessica Yu <jeyu@kernel.org>,
        kernel test robot <lkp@intel.com>,
        Miroslav Benes <mbenes@suse.cz>,
        Evgenii Shatokhin <eshatokhin@virtuozzo.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will@kernel.org>, Ingo Molnar <mingo@redhat.com>,
        Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Marios Pomonis <pomonis@google.com>,
        Sami Tolvanen <samitolvanen@google.com>,
        linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org,
        linux-arch@vger.kernel.org, live-patching@vger.kernel.org,
        llvm@lists.linux.dev
Subject: [PATCH v8 07/14] kallsyms: Hide layout
Date:   Thu,  2 Dec 2021 23:32:07 +0100
Message-Id: <20211202223214.72888-8-alexandr.lobakin@intel.com>
In-Reply-To: <20211202223214.72888-1-alexandr.lobakin@intel.com>
References: <20211202223214.72888-1-alexandr.lobakin@intel.com>
MIME-Version: 1.0
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From: Kristen Carlson Accardi <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>
Reported-by: kernel test robot <lkp@intel.com> # swap.cocci
Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com>
---
 kernel/kallsyms.c | 158 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 157 insertions(+), 1 deletion(-)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 3011bc33a5ba..ff9d8b651966 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -583,6 +583,12 @@ 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)
 {
@@ -830,7 +836,7 @@ 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
@@ -851,6 +857,156 @@ 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.
+ */
+#ifdef 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)
+{
+	u32 i, j;
+
+	for (i = size - 1; i > 0; i--) {
+		/* pick a random index from 0 to i */
+		j = get_random_u32() % (i + 1);
+
+		swap(indexes[i], indexes[j]);
+	}
+}
+
+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)
 {
-- 
2.33.1