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ftrace, kprobes: Support IPMODIFY flag to find IP modify conflict
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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.

Link: http://lkml.kernel.org/r/20141121102516.11844.27829.stgit@localhost.localdomain

Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Petr Mladek <pmladek@suse.cz>
Cc: Vojtech Pavlik <vojtech@suse.cz>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
[ fixed up some of the comments ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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@mhiramathitachi @rostedt
mhiramathitachi authored and rostedt committed Nov 21, 2014
1 parent a017784 commit f8b8be8
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Showing 3 changed files with 159 additions and 4 deletions.
5 changes: 5 additions & 0 deletions Documentation/trace/ftrace.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down
16 changes: 14 additions & 2 deletions include/linux/ftrace.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -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 with this flag set 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,
Expand All @@ -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
Expand Down Expand Up @@ -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
Expand All @@ -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)
Expand Down
142 changes: 140 additions & 2 deletions kernel/trace/ftrace.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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)
Expand All @@ -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.
Expand Down Expand Up @@ -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.
Expand Down Expand Up @@ -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 a 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;
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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)
Expand Down

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