[PATCH ftrace/core v6 2/5] ftrace, kprobes: Support IPMODIFY flag to find IP modify conflict

From: Masami Hiramatsu
Date: Thu Nov 20 2014 - 21:29:41 EST

Introduce FTRACE_OPS_FL_IPMODIFY to avoid conflict among
ftrace users who may modify regs->ip to change the execution
path. If two or more users modify the regs->ip on the same
function entry, one of them will be broken. So they must add
IPMODIFY flag and make sure that ftrace_set_filter_ip() succeeds.

Note that ftrace doesn't allow ftrace_ops which has IPMODIFY
flag to have notrace hash, and the ftrace_ops must have a
filter hash (so that the ftrace_ops can hook only specific
entries), because it strongly depends on the address and
must be allowed for only few selected functions.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Cc: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>

---
Changes in v6:
- Update to the latest ftrace tree (Trampoline).

Changes in v5:
- Update to the latest ftrace tree.

Changes in v4:
- Split kprobe's part from this patch.
- Add no-notrace hash check.
- Reject if the filter_hash is empty. Since IPMODIFY action
is very address sensitive, empty hash (means hooking all
functions) must not be allowed.

Changes in v3:
- Update for the latest ftrace/core.
- Add a comment about FTRACE_OPS_FL_* attribute flags.
- Don't check FTRACE_OPS_FL_SAVE_REGS in
__ftrace_hash_update_ipmodify().
- Fix comments.

Changes in v2:
- Add a description how __ftrace_hash_update_ipmodify() will
handle the given hashes (NULL and EMPTY_HASH cases).
- Clear FTRACE_OPS_FL_ENABLED after calling
__unregister_ftrace_function() in error path.
---
Documentation/trace/ftrace.txt | 5 +
include/linux/ftrace.h | 16 ++++-
kernel/trace/ftrace.c | 142 +++++++++++++++++++++++++++++++++++++++-
3 files changed, 159 insertions(+), 4 deletions(-)

diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
index 4da4261..f10f5f5 100644
--- a/Documentation/trace/ftrace.txt
+++ b/Documentation/trace/ftrace.txt
@@ -234,6 +234,11 @@ of ftrace. Here is a list of some of the key files:
will be displayed on the same line as the function that
is returning registers.

+ If the callback registered to be traced by a function with
+ the "ip modify" attribute (thus the regs->ip can be changed),
+ an 'I' will be displayed on the same line as the function that
+ can be overridden.
+
function_profile_enabled:

When set it will enable all functions with either the function
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 7b2616f..93cf047 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -61,6 +61,11 @@ ftrace_func_t ftrace_ops_get_func(struct ftrace_ops *ops);
/*
* FTRACE_OPS_FL_* bits denote the state of ftrace_ops struct and are
* set in the flags member.
+ * CONTROL, SAVE_REGS, SAVE_REGS_IF_SUPPORTED, RECURSION_SAFE, STUB and
+ * IPMODIFY are a kind of attribute flags which can be set only before
+ * registering the ftrace_ops, and can not be modified while registered.
+ * Changing those attribute flags after regsitering ftrace_ops will
+ * cause unexpected results.
*
* ENABLED - set/unset when ftrace_ops is registered/unregistered
* DYNAMIC - set when ftrace_ops is registered to denote dynamically
@@ -101,6 +106,10 @@ ftrace_func_t ftrace_ops_get_func(struct ftrace_ops *ops);
* The ftrace_ops trampoline can be set by the ftrace users, and
* in such cases the arch must not modify it. Only the arch ftrace
* core code should set this flag.
+ * IPMODIFY - The ops can modify the IP register. This can only be set with
+ * SAVE_REGS. If another ops is already registered for any of the
+ * functions that this ops will be registered for, then this ops
+ * will fail to register or set_filter_ip.
*/
enum {
FTRACE_OPS_FL_ENABLED = 1 << 0,
@@ -116,6 +125,7 @@ enum {
FTRACE_OPS_FL_REMOVING = 1 << 10,
FTRACE_OPS_FL_MODIFYING = 1 << 11,
FTRACE_OPS_FL_ALLOC_TRAMP = 1 << 12,
+ FTRACE_OPS_FL_IPMODIFY = 1 << 13,
};

#ifdef CONFIG_DYNAMIC_FTRACE
@@ -310,6 +320,7 @@ bool is_ftrace_trampoline(unsigned long addr);
* ENABLED - the function is being traced
* REGS - the record wants the function to save regs
* REGS_EN - the function is set up to save regs.
+ * IPMODIFY - the record allows for the IP address to be changed.
*
* When a new ftrace_ops is registered and wants a function to save
* pt_regs, the rec->flag REGS is set. When the function has been
@@ -323,10 +334,11 @@ enum {
FTRACE_FL_REGS_EN = (1UL << 29),
FTRACE_FL_TRAMP = (1UL << 28),
FTRACE_FL_TRAMP_EN = (1UL << 27),
+ FTRACE_FL_IPMODIFY = (1UL << 26),
};

-#define FTRACE_REF_MAX_SHIFT 27
-#define FTRACE_FL_BITS 5
+#define FTRACE_REF_MAX_SHIFT 26
+#define FTRACE_FL_BITS 6
#define FTRACE_FL_MASKED_BITS ((1UL << FTRACE_FL_BITS) - 1)
#define FTRACE_FL_MASK (FTRACE_FL_MASKED_BITS << FTRACE_REF_MAX_SHIFT)
#define FTRACE_REF_MAX ((1UL << FTRACE_REF_MAX_SHIFT) - 1)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index fa0f36b..baa2c4d 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1358,6 +1358,9 @@ ftrace_hash_rec_disable_modify(struct ftrace_ops *ops, int filter_hash);
static void
ftrace_hash_rec_enable_modify(struct ftrace_ops *ops, int filter_hash);

+static int ftrace_hash_ipmodify_update(struct ftrace_ops *ops,
+ struct ftrace_hash *new_hash);
+
static int
ftrace_hash_move(struct ftrace_ops *ops, int enable,
struct ftrace_hash **dst, struct ftrace_hash *src)
@@ -1368,8 +1371,13 @@ ftrace_hash_move(struct ftrace_ops *ops, int enable,
struct ftrace_hash *new_hash;
int size = src->count;
int bits = 0;
+ int ret;
int i;

+ /* Reject setting notrace hash on IPMODIFY ftrace_ops */
+ if (ops->flags & FTRACE_OPS_FL_IPMODIFY && !enable)
+ return -EINVAL;
+
/*
* If the new source is empty, just free dst and assign it
* the empty_hash.
@@ -1403,6 +1411,16 @@ ftrace_hash_move(struct ftrace_ops *ops, int enable,
}

update:
+ /* Make sure this can be applied if it is IPMODIFY ftrace_ops */
+ if (enable) {
+ /* IPMODIFY should be updated only when filter_hash updating */
+ ret = ftrace_hash_ipmodify_update(ops, new_hash);
+ if (ret < 0) {
+ free_ftrace_hash(new_hash);
+ return ret;
+ }
+ }
+
/*
* Remove the current set, update the hash and add
* them back.
@@ -1767,6 +1785,114 @@ static void ftrace_hash_rec_enable_modify(struct ftrace_ops *ops,
ftrace_hash_rec_update_modify(ops, filter_hash, 1);
}

+/*
+ * Try to update IPMODIFY flag on each ftrace_rec. Return 0 if it is OK
+ * or no-needed to update, -EBUSY if it detects a conflict of the flag
+ * on a ftrace_rec, and -EINVAL if the new_hash tries to trace all recs.
+ * Note that old_hash and new_hash has below meanings
+ * - If the hash is NULL, it hits all recs (if IPMODIFY is set, this is rejected)
+ * - If the hash is EMPTY_HASH, it hits nothing
+ * - Anything else hits the recs which match the hash entries.
+ */
+static int __ftrace_hash_update_ipmodify(struct ftrace_ops *ops,
+ struct ftrace_hash *old_hash,
+ struct ftrace_hash *new_hash)
+{
+ struct ftrace_page *pg;
+ struct dyn_ftrace *rec, *end = NULL;
+ int in_old, in_new;
+
+ /* Only update if the ops has been registered */
+ if (!(ops->flags & FTRACE_OPS_FL_ENABLED))
+ return 0;
+
+ if (!(ops->flags & FTRACE_OPS_FL_IPMODIFY))
+ return 0;
+
+ /*
+ * Since the IPMODIFY is very address sensitive action, we do not allow
+ * ftrace_ops to set all functions to new hash.
+ */
+ if (!new_hash || !old_hash)
+ return -EINVAL;
+
+ /* Update rec->flags */
+ do_for_each_ftrace_rec(pg, rec) {
+ /* We need to update only differences of filter_hash */
+ in_old = !!ftrace_lookup_ip(old_hash, rec->ip);
+ in_new = !!ftrace_lookup_ip(new_hash, rec->ip);
+ if (in_old == in_new)
+ continue;
+
+ if (in_new) {
+ /* New entries must ensure no others are using it */
+ if (rec->flags & FTRACE_FL_IPMODIFY)
+ goto rollback;
+ rec->flags |= FTRACE_FL_IPMODIFY;
+ } else /* Removed entry */
+ rec->flags &= ~FTRACE_FL_IPMODIFY;
+ } while_for_each_ftrace_rec();
+
+ return 0;
+
+rollback:
+ end = rec;
+
+ /* Roll back what we did above */
+ do_for_each_ftrace_rec(pg, rec) {
+ if (rec == end)
+ goto err_out;
+
+ in_old = !!ftrace_lookup_ip(old_hash, rec->ip);
+ in_new = !!ftrace_lookup_ip(new_hash, rec->ip);
+ if (in_old == in_new)
+ continue;
+
+ if (in_new)
+ rec->flags &= ~FTRACE_FL_IPMODIFY;
+ else
+ rec->flags |= FTRACE_FL_IPMODIFY;
+ } while_for_each_ftrace_rec();
+
+err_out:
+ return -EBUSY;
+}
+
+static int ftrace_hash_ipmodify_enable(struct ftrace_ops *ops)
+{
+ struct ftrace_hash *hash = ops->func_hash->filter_hash;
+
+ if (ftrace_hash_empty(hash))
+ hash = NULL;
+
+ return __ftrace_hash_update_ipmodify(ops, EMPTY_HASH, hash);
+}
+
+/* Disabling always succeeds */
+static void ftrace_hash_ipmodify_disable(struct ftrace_ops *ops)
+{
+ struct ftrace_hash *hash = ops->func_hash->filter_hash;
+
+ if (ftrace_hash_empty(hash))
+ hash = NULL;
+
+ __ftrace_hash_update_ipmodify(ops, hash, EMPTY_HASH);
+}
+
+static int ftrace_hash_ipmodify_update(struct ftrace_ops *ops,
+ struct ftrace_hash *new_hash)
+{
+ struct ftrace_hash *old_hash = ops->func_hash->filter_hash;
+
+ if (ftrace_hash_empty(old_hash))
+ old_hash = NULL;
+
+ if (ftrace_hash_empty(new_hash))
+ new_hash = NULL;
+
+ return __ftrace_hash_update_ipmodify(ops, old_hash, new_hash);
+}
+
static void print_ip_ins(const char *fmt, unsigned char *p)
{
int i;
@@ -2436,6 +2562,15 @@ static int ftrace_startup(struct ftrace_ops *ops, int command)
*/
ops->flags |= FTRACE_OPS_FL_ENABLED | FTRACE_OPS_FL_ADDING;

+ ret = ftrace_hash_ipmodify_enable(ops);
+ if (ret < 0) {
+ /* Rollback registration process */
+ __unregister_ftrace_function(ops);
+ ftrace_start_up--;
+ ops->flags &= ~FTRACE_OPS_FL_ENABLED;
+ return ret;
+ }
+
ftrace_hash_rec_enable(ops, 1);

ftrace_startup_enable(command);
@@ -2464,6 +2599,8 @@ static int ftrace_shutdown(struct ftrace_ops *ops, int command)
*/
WARN_ON_ONCE(ftrace_start_up < 0);

+ /* Disabling ipmodify never fails */
+ ftrace_hash_ipmodify_disable(ops);
ftrace_hash_rec_disable(ops, 1);

ops->flags &= ~FTRACE_OPS_FL_ENABLED;
@@ -3058,9 +3195,10 @@ static int t_show(struct seq_file *m, void *v)
if (iter->flags & FTRACE_ITER_ENABLED) {
struct ftrace_ops *ops = NULL;

- seq_printf(m, " (%ld)%s",
+ seq_printf(m, " (%ld)%s%s",
ftrace_rec_count(rec),
- rec->flags & FTRACE_FL_REGS ? " R" : " ");
+ rec->flags & FTRACE_FL_REGS ? " R" : " ",
+ rec->flags & FTRACE_FL_IPMODIFY ? " I" : " ");
if (rec->flags & FTRACE_FL_TRAMP_EN) {
ops = ftrace_find_tramp_ops_any(rec);
if (ops)


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