* [for-linus][PATCH 1/4] tracing: Fix test_event_printk() to process entire print argument
[not found] <20241218013828.733621977@goodmis.org>
@ 2024-12-18 1:38 ` Steven Rostedt
2024-12-18 1:38 ` [for-linus][PATCH 2/4] tracing: Add missing helper functions in event pointer dereference check Steven Rostedt
` (2 subsequent siblings)
3 siblings, 0 replies; 4+ messages in thread
From: Steven Rostedt @ 2024-12-18 1:38 UTC (permalink / raw)
To: linux-kernel
Cc: Masami Hiramatsu, Mark Rutland, Mathieu Desnoyers, Andrew Morton,
stable, Al Viro, Linus Torvalds
From: Steven Rostedt <rostedt@goodmis.org>
The test_event_printk() analyzes print formats of trace events looking for
cases where it may dereference a pointer that is not in the ring buffer
which can possibly be a bug when the trace event is read from the ring
buffer and the content of that pointer no longer exists.
The function needs to accurately go from one print format argument to the
next. It handles quotes and parenthesis that may be included in an
argument. When it finds the start of the next argument, it uses a simple
"c = strstr(fmt + i, ',')" to find the end of that argument!
In order to include "%s" dereferencing, it needs to process the entire
content of the print format argument and not just the content of the first
',' it finds. As there may be content like:
({ const char *saved_ptr = trace_seq_buffer_ptr(p); static const char
*access_str[] = { "---", "--x", "w--", "w-x", "-u-", "-ux", "wu-", "wux"
}; union kvm_mmu_page_role role; role.word = REC->role;
trace_seq_printf(p, "sp gen %u gfn %llx l%u %u-byte q%u%s %s%s" " %snxe
%sad root %u %s%c", REC->mmu_valid_gen, REC->gfn, role.level,
role.has_4_byte_gpte ? 4 : 8, role.quadrant, role.direct ? " direct" : "",
access_str[role.access], role.invalid ? " invalid" : "", role.efer_nx ? ""
: "!", role.ad_disabled ? "!" : "", REC->root_count, REC->unsync ?
"unsync" : "sync", 0); saved_ptr; })
Which is an example of a full argument of an existing event. As the code
already handles finding the next print format argument, process the
argument at the end of it and not the start of it. This way it has both
the start of the argument as well as the end of it.
Add a helper function "process_pointer()" that will do the processing during
the loop as well as at the end. It also makes the code cleaner and easier
to read.
Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/20241217024720.362271189@goodmis.org
Fixes: 5013f454a352c ("tracing: Add check of trace event print fmts for dereferencing pointers")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
kernel/trace/trace_events.c | 82 ++++++++++++++++++++++++-------------
1 file changed, 53 insertions(+), 29 deletions(-)
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 77e68efbd43e..14e160a5b905 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -265,8 +265,7 @@ static bool test_field(const char *fmt, struct trace_event_call *call)
len = p - fmt;
for (; field->type; field++) {
- if (strncmp(field->name, fmt, len) ||
- field->name[len])
+ if (strncmp(field->name, fmt, len) || field->name[len])
continue;
array_descriptor = strchr(field->type, '[');
/* This is an array and is OK to dereference. */
@@ -275,6 +274,32 @@ static bool test_field(const char *fmt, struct trace_event_call *call)
return false;
}
+/* Return true if the argument pointer is safe */
+static bool process_pointer(const char *fmt, int len, struct trace_event_call *call)
+{
+ const char *r, *e, *a;
+
+ e = fmt + len;
+
+ /* Find the REC-> in the argument */
+ r = strstr(fmt, "REC->");
+ if (r && r < e) {
+ /*
+ * Addresses of events on the buffer, or an array on the buffer is
+ * OK to dereference. There's ways to fool this, but
+ * this is to catch common mistakes, not malicious code.
+ */
+ a = strchr(fmt, '&');
+ if ((a && (a < r)) || test_field(r, call))
+ return true;
+ } else if ((r = strstr(fmt, "__get_dynamic_array(")) && r < e) {
+ return true;
+ } else if ((r = strstr(fmt, "__get_sockaddr(")) && r < e) {
+ return true;
+ }
+ return false;
+}
+
/*
* Examine the print fmt of the event looking for unsafe dereference
* pointers using %p* that could be recorded in the trace event and
@@ -285,12 +310,12 @@ static void test_event_printk(struct trace_event_call *call)
{
u64 dereference_flags = 0;
bool first = true;
- const char *fmt, *c, *r, *a;
+ const char *fmt;
int parens = 0;
char in_quote = 0;
int start_arg = 0;
int arg = 0;
- int i;
+ int i, e;
fmt = call->print_fmt;
@@ -403,42 +428,41 @@ static void test_event_printk(struct trace_event_call *call)
case ',':
if (in_quote || parens)
continue;
+ e = i;
i++;
while (isspace(fmt[i]))
i++;
- start_arg = i;
- if (!(dereference_flags & (1ULL << arg)))
- goto next_arg;
- /* Find the REC-> in the argument */
- c = strchr(fmt + i, ',');
- r = strstr(fmt + i, "REC->");
- if (r && (!c || r < c)) {
- /*
- * Addresses of events on the buffer,
- * or an array on the buffer is
- * OK to dereference.
- * There's ways to fool this, but
- * this is to catch common mistakes,
- * not malicious code.
- */
- a = strchr(fmt + i, '&');
- if ((a && (a < r)) || test_field(r, call))
+ /*
+ * If start_arg is zero, then this is the start of the
+ * first argument. The processing of the argument happens
+ * when the end of the argument is found, as it needs to
+ * handle paranthesis and such.
+ */
+ if (!start_arg) {
+ start_arg = i;
+ /* Balance out the i++ in the for loop */
+ i--;
+ continue;
+ }
+
+ if (dereference_flags & (1ULL << arg)) {
+ if (process_pointer(fmt + start_arg, e - start_arg, call))
dereference_flags &= ~(1ULL << arg);
- } else if ((r = strstr(fmt + i, "__get_dynamic_array(")) &&
- (!c || r < c)) {
- dereference_flags &= ~(1ULL << arg);
- } else if ((r = strstr(fmt + i, "__get_sockaddr(")) &&
- (!c || r < c)) {
- dereference_flags &= ~(1ULL << arg);
}
- next_arg:
- i--;
+ start_arg = i;
arg++;
+ /* Balance out the i++ in the for loop */
+ i--;
}
}
+ if (dereference_flags & (1ULL << arg)) {
+ if (process_pointer(fmt + start_arg, i - start_arg, call))
+ dereference_flags &= ~(1ULL << arg);
+ }
+
/*
* If you triggered the below warning, the trace event reported
* uses an unsafe dereference pointer %p*. As the data stored
--
2.45.2
^ permalink raw reply related [flat|nested] 4+ messages in thread* [for-linus][PATCH 3/4] tracing: Add "%s" check in test_event_printk()
[not found] <20241218013828.733621977@goodmis.org>
2024-12-18 1:38 ` [for-linus][PATCH 1/4] tracing: Fix test_event_printk() to process entire print argument Steven Rostedt
2024-12-18 1:38 ` [for-linus][PATCH 2/4] tracing: Add missing helper functions in event pointer dereference check Steven Rostedt
@ 2024-12-18 1:38 ` Steven Rostedt
2024-12-18 1:38 ` [for-linus][PATCH 4/4] tracing: Check "%s" dereference via the field and not the TP_printk format Steven Rostedt
3 siblings, 0 replies; 4+ messages in thread
From: Steven Rostedt @ 2024-12-18 1:38 UTC (permalink / raw)
To: linux-kernel
Cc: Masami Hiramatsu, Mark Rutland, Mathieu Desnoyers, Andrew Morton,
stable, Al Viro, Linus Torvalds
From: Steven Rostedt <rostedt@goodmis.org>
The test_event_printk() code makes sure that when a trace event is
registered, any dereferenced pointers in from the event's TP_printk() are
pointing to content in the ring buffer. But currently it does not handle
"%s", as there's cases where the string pointer saved in the ring buffer
points to a static string in the kernel that will never be freed. As that
is a valid case, the pointer needs to be checked at runtime.
Currently the runtime check is done via trace_check_vprintf(), but to not
have to replicate everything in vsnprintf() it does some logic with the
va_list that may not be reliable across architectures. In order to get rid
of that logic, more work in the test_event_printk() needs to be done. Some
of the strings can be validated at this time when it is obvious the string
is valid because the string will be saved in the ring buffer content.
Do all the validation of strings in the ring buffer at boot in
test_event_printk(), and make sure that the field of the strings that
point into the kernel are accessible. This will allow adding checks at
runtime that will validate the fields themselves and not rely on paring
the TP_printk() format at runtime.
Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/20241217024720.685917008@goodmis.org
Fixes: 5013f454a352c ("tracing: Add check of trace event print fmts for dereferencing pointers")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
kernel/trace/trace_events.c | 104 ++++++++++++++++++++++++++++++------
1 file changed, 89 insertions(+), 15 deletions(-)
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index df75c06bb23f..521ad2fd1fe7 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -244,19 +244,16 @@ int trace_event_get_offsets(struct trace_event_call *call)
return tail->offset + tail->size;
}
-/*
- * Check if the referenced field is an array and return true,
- * as arrays are OK to dereference.
- */
-static bool test_field(const char *fmt, struct trace_event_call *call)
+
+static struct trace_event_fields *find_event_field(const char *fmt,
+ struct trace_event_call *call)
{
struct trace_event_fields *field = call->class->fields_array;
- const char *array_descriptor;
const char *p = fmt;
int len;
if (!(len = str_has_prefix(fmt, "REC->")))
- return false;
+ return NULL;
fmt += len;
for (p = fmt; *p; p++) {
if (!isalnum(*p) && *p != '_')
@@ -267,11 +264,26 @@ static bool test_field(const char *fmt, struct trace_event_call *call)
for (; field->type; field++) {
if (strncmp(field->name, fmt, len) || field->name[len])
continue;
- array_descriptor = strchr(field->type, '[');
- /* This is an array and is OK to dereference. */
- return array_descriptor != NULL;
+
+ return field;
}
- return false;
+ return NULL;
+}
+
+/*
+ * Check if the referenced field is an array and return true,
+ * as arrays are OK to dereference.
+ */
+static bool test_field(const char *fmt, struct trace_event_call *call)
+{
+ struct trace_event_fields *field;
+
+ field = find_event_field(fmt, call);
+ if (!field)
+ return false;
+
+ /* This is an array and is OK to dereference. */
+ return strchr(field->type, '[') != NULL;
}
/* Look for a string within an argument */
@@ -317,6 +329,53 @@ static bool process_pointer(const char *fmt, int len, struct trace_event_call *c
return false;
}
+/* Return true if the string is safe */
+static bool process_string(const char *fmt, int len, struct trace_event_call *call)
+{
+ const char *r, *e, *s;
+
+ e = fmt + len;
+
+ /*
+ * There are several helper functions that return strings.
+ * If the argument contains a function, then assume its field is valid.
+ * It is considered that the argument has a function if it has:
+ * alphanumeric or '_' before a parenthesis.
+ */
+ s = fmt;
+ do {
+ r = strstr(s, "(");
+ if (!r || r >= e)
+ break;
+ for (int i = 1; r - i >= s; i++) {
+ char ch = *(r - i);
+ if (isspace(ch))
+ continue;
+ if (isalnum(ch) || ch == '_')
+ return true;
+ /* Anything else, this isn't a function */
+ break;
+ }
+ /* A function could be wrapped in parethesis, try the next one */
+ s = r + 1;
+ } while (s < e);
+
+ /*
+ * If there's any strings in the argument consider this arg OK as it
+ * could be: REC->field ? "foo" : "bar" and we don't want to get into
+ * verifying that logic here.
+ */
+ if (find_print_string(fmt, "\"", e))
+ return true;
+
+ /* Dereferenced strings are also valid like any other pointer */
+ if (process_pointer(fmt, len, call))
+ return true;
+
+ /* Make sure the field is found, and consider it OK for now if it is */
+ return find_event_field(fmt, call) != NULL;
+}
+
/*
* Examine the print fmt of the event looking for unsafe dereference
* pointers using %p* that could be recorded in the trace event and
@@ -326,6 +385,7 @@ static bool process_pointer(const char *fmt, int len, struct trace_event_call *c
static void test_event_printk(struct trace_event_call *call)
{
u64 dereference_flags = 0;
+ u64 string_flags = 0;
bool first = true;
const char *fmt;
int parens = 0;
@@ -416,8 +476,16 @@ static void test_event_printk(struct trace_event_call *call)
star = true;
continue;
}
- if ((fmt[i + j] == 's') && star)
- arg++;
+ if ((fmt[i + j] == 's')) {
+ if (star)
+ arg++;
+ if (WARN_ONCE(arg == 63,
+ "Too many args for event: %s",
+ trace_event_name(call)))
+ return;
+ dereference_flags |= 1ULL << arg;
+ string_flags |= 1ULL << arg;
+ }
break;
}
break;
@@ -464,7 +532,10 @@ static void test_event_printk(struct trace_event_call *call)
}
if (dereference_flags & (1ULL << arg)) {
- if (process_pointer(fmt + start_arg, e - start_arg, call))
+ if (string_flags & (1ULL << arg)) {
+ if (process_string(fmt + start_arg, e - start_arg, call))
+ dereference_flags &= ~(1ULL << arg);
+ } else if (process_pointer(fmt + start_arg, e - start_arg, call))
dereference_flags &= ~(1ULL << arg);
}
@@ -476,7 +547,10 @@ static void test_event_printk(struct trace_event_call *call)
}
if (dereference_flags & (1ULL << arg)) {
- if (process_pointer(fmt + start_arg, i - start_arg, call))
+ if (string_flags & (1ULL << arg)) {
+ if (process_string(fmt + start_arg, i - start_arg, call))
+ dereference_flags &= ~(1ULL << arg);
+ } else if (process_pointer(fmt + start_arg, i - start_arg, call))
dereference_flags &= ~(1ULL << arg);
}
--
2.45.2
^ permalink raw reply related [flat|nested] 4+ messages in thread* [for-linus][PATCH 4/4] tracing: Check "%s" dereference via the field and not the TP_printk format
[not found] <20241218013828.733621977@goodmis.org>
` (2 preceding siblings ...)
2024-12-18 1:38 ` [for-linus][PATCH 3/4] tracing: Add "%s" check in test_event_printk() Steven Rostedt
@ 2024-12-18 1:38 ` Steven Rostedt
3 siblings, 0 replies; 4+ messages in thread
From: Steven Rostedt @ 2024-12-18 1:38 UTC (permalink / raw)
To: linux-kernel
Cc: Masami Hiramatsu, Mark Rutland, Mathieu Desnoyers, Andrew Morton,
stable, Al Viro, Linus Torvalds
From: Steven Rostedt <rostedt@goodmis.org>
The TP_printk() portion of a trace event is executed at the time a event
is read from the trace. This can happen seconds, minutes, hours, days,
months, years possibly later since the event was recorded. If the print
format contains a dereference to a string via "%s", and that string was
allocated, there's a chance that string could be freed before it is read
by the trace file.
To protect against such bugs, there are two functions that verify the
event. The first one is test_event_printk(), which is called when the
event is created. It reads the TP_printk() format as well as its arguments
to make sure nothing may be dereferencing a pointer that was not copied
into the ring buffer along with the event. If it is, it will trigger a
WARN_ON().
For strings that use "%s", it is not so easy. The string may not reside in
the ring buffer but may still be valid. Strings that are static and part
of the kernel proper which will not be freed for the life of the running
system, are safe to dereference. But to know if it is a pointer to a
static string or to something on the heap can not be determined until the
event is triggered.
This brings us to the second function that tests for the bad dereferencing
of strings, trace_check_vprintf(). It would walk through the printf format
looking for "%s", and when it finds it, it would validate that the pointer
is safe to read. If not, it would produces a WARN_ON() as well and write
into the ring buffer "[UNSAFE-MEMORY]".
The problem with this is how it used va_list to have vsnprintf() handle
all the cases that it didn't need to check. Instead of re-implementing
vsnprintf(), it would make a copy of the format up to the %s part, and
call vsnprintf() with the current va_list ap variable, where the ap would
then be ready to point at the string in question.
For architectures that passed va_list by reference this was possible. For
architectures that passed it by copy it was not. A test_can_verify()
function was used to differentiate between the two, and if it wasn't
possible, it would disable it.
Even for architectures where this was feasible, it was a stretch to rely
on such a method that is undocumented, and could cause issues later on
with new optimizations of the compiler.
Instead, the first function test_event_printk() was updated to look at
"%s" as well. If the "%s" argument is a pointer outside the event in the
ring buffer, it would find the field type of the event that is the problem
and mark the structure with a new flag called "needs_test". The event
itself will be marked by TRACE_EVENT_FL_TEST_STR to let it be known that
this event has a field that needs to be verified before the event can be
printed using the printf format.
When the event fields are created from the field type structure, the
fields would copy the field type's "needs_test" value.
Finally, before being printed, a new function ignore_event() is called
which will check if the event has the TEST_STR flag set (if not, it
returns false). If the flag is set, it then iterates through the events
fields looking for the ones that have the "needs_test" flag set.
Then it uses the offset field from the field structure to find the pointer
in the ring buffer event. It runs the tests to make sure that pointer is
safe to print and if not, it triggers the WARN_ON() and also adds to the
trace output that the event in question has an unsafe memory access.
The ignore_event() makes the trace_check_vprintf() obsolete so it is
removed.
Link: https://lore.kernel.org/all/CAHk-=wh3uOnqnZPpR0PeLZZtyWbZLboZ7cHLCKRWsocvs9Y7hQ@mail.gmail.com/
Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/20241217024720.848621576@goodmis.org
Fixes: 5013f454a352c ("tracing: Add check of trace event print fmts for dereferencing pointers")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
include/linux/trace_events.h | 6 +-
kernel/trace/trace.c | 255 ++++++++---------------------------
kernel/trace/trace.h | 6 +-
kernel/trace/trace_events.c | 32 +++--
kernel/trace/trace_output.c | 6 +-
5 files changed, 88 insertions(+), 217 deletions(-)
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 2a5df5b62cfc..91b8ffbdfa8c 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -273,7 +273,8 @@ struct trace_event_fields {
const char *name;
const int size;
const int align;
- const int is_signed;
+ const unsigned int is_signed:1;
+ unsigned int needs_test:1;
const int filter_type;
const int len;
};
@@ -324,6 +325,7 @@ enum {
TRACE_EVENT_FL_EPROBE_BIT,
TRACE_EVENT_FL_FPROBE_BIT,
TRACE_EVENT_FL_CUSTOM_BIT,
+ TRACE_EVENT_FL_TEST_STR_BIT,
};
/*
@@ -340,6 +342,7 @@ enum {
* CUSTOM - Event is a custom event (to be attached to an exsiting tracepoint)
* This is set when the custom event has not been attached
* to a tracepoint yet, then it is cleared when it is.
+ * TEST_STR - The event has a "%s" that points to a string outside the event
*/
enum {
TRACE_EVENT_FL_CAP_ANY = (1 << TRACE_EVENT_FL_CAP_ANY_BIT),
@@ -352,6 +355,7 @@ enum {
TRACE_EVENT_FL_EPROBE = (1 << TRACE_EVENT_FL_EPROBE_BIT),
TRACE_EVENT_FL_FPROBE = (1 << TRACE_EVENT_FL_FPROBE_BIT),
TRACE_EVENT_FL_CUSTOM = (1 << TRACE_EVENT_FL_CUSTOM_BIT),
+ TRACE_EVENT_FL_TEST_STR = (1 << TRACE_EVENT_FL_TEST_STR_BIT),
};
#define TRACE_EVENT_FL_UKPROBE (TRACE_EVENT_FL_KPROBE | TRACE_EVENT_FL_UPROBE)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index be62f0ea1814..7cc18b9bce27 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3611,17 +3611,12 @@ char *trace_iter_expand_format(struct trace_iterator *iter)
}
/* Returns true if the string is safe to dereference from an event */
-static bool trace_safe_str(struct trace_iterator *iter, const char *str,
- bool star, int len)
+static bool trace_safe_str(struct trace_iterator *iter, const char *str)
{
unsigned long addr = (unsigned long)str;
struct trace_event *trace_event;
struct trace_event_call *event;
- /* Ignore strings with no length */
- if (star && !len)
- return true;
-
/* OK if part of the event data */
if ((addr >= (unsigned long)iter->ent) &&
(addr < (unsigned long)iter->ent + iter->ent_size))
@@ -3661,181 +3656,69 @@ static bool trace_safe_str(struct trace_iterator *iter, const char *str,
return false;
}
-static DEFINE_STATIC_KEY_FALSE(trace_no_verify);
-
-static int test_can_verify_check(const char *fmt, ...)
-{
- char buf[16];
- va_list ap;
- int ret;
-
- /*
- * The verifier is dependent on vsnprintf() modifies the va_list
- * passed to it, where it is sent as a reference. Some architectures
- * (like x86_32) passes it by value, which means that vsnprintf()
- * does not modify the va_list passed to it, and the verifier
- * would then need to be able to understand all the values that
- * vsnprintf can use. If it is passed by value, then the verifier
- * is disabled.
- */
- va_start(ap, fmt);
- vsnprintf(buf, 16, "%d", ap);
- ret = va_arg(ap, int);
- va_end(ap);
-
- return ret;
-}
-
-static void test_can_verify(void)
-{
- if (!test_can_verify_check("%d %d", 0, 1)) {
- pr_info("trace event string verifier disabled\n");
- static_branch_inc(&trace_no_verify);
- }
-}
-
/**
- * trace_check_vprintf - Check dereferenced strings while writing to the seq buffer
+ * ignore_event - Check dereferenced fields while writing to the seq buffer
* @iter: The iterator that holds the seq buffer and the event being printed
- * @fmt: The format used to print the event
- * @ap: The va_list holding the data to print from @fmt.
*
- * This writes the data into the @iter->seq buffer using the data from
- * @fmt and @ap. If the format has a %s, then the source of the string
- * is examined to make sure it is safe to print, otherwise it will
- * warn and print "[UNSAFE MEMORY]" in place of the dereferenced string
- * pointer.
+ * At boot up, test_event_printk() will flag any event that dereferences
+ * a string with "%s" that does exist in the ring buffer. It may still
+ * be valid, as the string may point to a static string in the kernel
+ * rodata that never gets freed. But if the string pointer is pointing
+ * to something that was allocated, there's a chance that it can be freed
+ * by the time the user reads the trace. This would cause a bad memory
+ * access by the kernel and possibly crash the system.
+ *
+ * This function will check if the event has any fields flagged as needing
+ * to be checked at runtime and perform those checks.
+ *
+ * If it is found that a field is unsafe, it will write into the @iter->seq
+ * a message stating what was found to be unsafe.
+ *
+ * @return: true if the event is unsafe and should be ignored,
+ * false otherwise.
*/
-void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
- va_list ap)
+bool ignore_event(struct trace_iterator *iter)
{
- long text_delta = 0;
- long data_delta = 0;
- const char *p = fmt;
- const char *str;
- bool good;
- int i, j;
+ struct ftrace_event_field *field;
+ struct trace_event *trace_event;
+ struct trace_event_call *event;
+ struct list_head *head;
+ struct trace_seq *seq;
+ const void *ptr;
- if (WARN_ON_ONCE(!fmt))
- return;
+ trace_event = ftrace_find_event(iter->ent->type);
- if (static_branch_unlikely(&trace_no_verify))
- goto print;
+ seq = &iter->seq;
- /*
- * When the kernel is booted with the tp_printk command line
- * parameter, trace events go directly through to printk().
- * It also is checked by this function, but it does not
- * have an associated trace_array (tr) for it.
- */
- if (iter->tr) {
- text_delta = iter->tr->text_delta;
- data_delta = iter->tr->data_delta;
+ if (!trace_event) {
+ trace_seq_printf(seq, "EVENT ID %d NOT FOUND?\n", iter->ent->type);
+ return true;
}
- /* Don't bother checking when doing a ftrace_dump() */
- if (iter->fmt == static_fmt_buf)
- goto print;
-
- while (*p) {
- bool star = false;
- int len = 0;
-
- j = 0;
-
- /*
- * We only care about %s and variants
- * as well as %p[sS] if delta is non-zero
- */
- for (i = 0; p[i]; i++) {
- if (i + 1 >= iter->fmt_size) {
- /*
- * If we can't expand the copy buffer,
- * just print it.
- */
- if (!trace_iter_expand_format(iter))
- goto print;
- }
-
- if (p[i] == '\\' && p[i+1]) {
- i++;
- continue;
- }
- if (p[i] == '%') {
- /* Need to test cases like %08.*s */
- for (j = 1; p[i+j]; j++) {
- if (isdigit(p[i+j]) ||
- p[i+j] == '.')
- continue;
- if (p[i+j] == '*') {
- star = true;
- continue;
- }
- break;
- }
- if (p[i+j] == 's')
- break;
-
- if (text_delta && p[i+1] == 'p' &&
- ((p[i+2] == 's' || p[i+2] == 'S')))
- break;
-
- star = false;
- }
- j = 0;
- }
- /* If no %s found then just print normally */
- if (!p[i])
- break;
-
- /* Copy up to the %s, and print that */
- strncpy(iter->fmt, p, i);
- iter->fmt[i] = '\0';
- trace_seq_vprintf(&iter->seq, iter->fmt, ap);
+ event = container_of(trace_event, struct trace_event_call, event);
+ if (!(event->flags & TRACE_EVENT_FL_TEST_STR))
+ return false;
- /* Add delta to %pS pointers */
- if (p[i+1] == 'p') {
- unsigned long addr;
- char fmt[4];
+ head = trace_get_fields(event);
+ if (!head) {
+ trace_seq_printf(seq, "FIELDS FOR EVENT '%s' NOT FOUND?\n",
+ trace_event_name(event));
+ return true;
+ }
- fmt[0] = '%';
- fmt[1] = 'p';
- fmt[2] = p[i+2]; /* Either %ps or %pS */
- fmt[3] = '\0';
+ /* Offsets are from the iter->ent that points to the raw event */
+ ptr = iter->ent;
- addr = va_arg(ap, unsigned long);
- addr += text_delta;
- trace_seq_printf(&iter->seq, fmt, (void *)addr);
+ list_for_each_entry(field, head, link) {
+ const char *str;
+ bool good;
- p += i + 3;
+ if (!field->needs_test)
continue;
- }
- /*
- * If iter->seq is full, the above call no longer guarantees
- * that ap is in sync with fmt processing, and further calls
- * to va_arg() can return wrong positional arguments.
- *
- * Ensure that ap is no longer used in this case.
- */
- if (iter->seq.full) {
- p = "";
- break;
- }
-
- if (star)
- len = va_arg(ap, int);
-
- /* The ap now points to the string data of the %s */
- str = va_arg(ap, const char *);
+ str = *(const char **)(ptr + field->offset);
- good = trace_safe_str(iter, str, star, len);
-
- /* Could be from the last boot */
- if (data_delta && !good) {
- str += data_delta;
- good = trace_safe_str(iter, str, star, len);
- }
+ good = trace_safe_str(iter, str);
/*
* If you hit this warning, it is likely that the
@@ -3846,44 +3729,14 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
* instead. See samples/trace_events/trace-events-sample.h
* for reference.
*/
- if (WARN_ONCE(!good, "fmt: '%s' current_buffer: '%s'",
- fmt, seq_buf_str(&iter->seq.seq))) {
- int ret;
-
- /* Try to safely read the string */
- if (star) {
- if (len + 1 > iter->fmt_size)
- len = iter->fmt_size - 1;
- if (len < 0)
- len = 0;
- ret = copy_from_kernel_nofault(iter->fmt, str, len);
- iter->fmt[len] = 0;
- star = false;
- } else {
- ret = strncpy_from_kernel_nofault(iter->fmt, str,
- iter->fmt_size);
- }
- if (ret < 0)
- trace_seq_printf(&iter->seq, "(0x%px)", str);
- else
- trace_seq_printf(&iter->seq, "(0x%px:%s)",
- str, iter->fmt);
- str = "[UNSAFE-MEMORY]";
- strcpy(iter->fmt, "%s");
- } else {
- strncpy(iter->fmt, p + i, j + 1);
- iter->fmt[j+1] = '\0';
+ if (WARN_ONCE(!good, "event '%s' has unsafe pointer field '%s'",
+ trace_event_name(event), field->name)) {
+ trace_seq_printf(seq, "EVENT %s: HAS UNSAFE POINTER FIELD '%s'\n",
+ trace_event_name(event), field->name);
+ return true;
}
- if (star)
- trace_seq_printf(&iter->seq, iter->fmt, len, str);
- else
- trace_seq_printf(&iter->seq, iter->fmt, str);
-
- p += i + j + 1;
}
- print:
- if (*p)
- trace_seq_vprintf(&iter->seq, p, ap);
+ return false;
}
const char *trace_event_format(struct trace_iterator *iter, const char *fmt)
@@ -10777,8 +10630,6 @@ __init static int tracer_alloc_buffers(void)
register_snapshot_cmd();
- test_can_verify();
-
return 0;
out_free_pipe_cpumask:
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 266740b4e121..9691b47b5f3d 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -667,9 +667,8 @@ void trace_buffer_unlock_commit_nostack(struct trace_buffer *buffer,
bool trace_is_tracepoint_string(const char *str);
const char *trace_event_format(struct trace_iterator *iter, const char *fmt);
-void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
- va_list ap) __printf(2, 0);
char *trace_iter_expand_format(struct trace_iterator *iter);
+bool ignore_event(struct trace_iterator *iter);
int trace_empty(struct trace_iterator *iter);
@@ -1413,7 +1412,8 @@ struct ftrace_event_field {
int filter_type;
int offset;
int size;
- int is_signed;
+ unsigned int is_signed:1;
+ unsigned int needs_test:1;
int len;
};
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 521ad2fd1fe7..1545cc8b49d0 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -82,7 +82,7 @@ static int system_refcount_dec(struct event_subsystem *system)
}
static struct ftrace_event_field *
-__find_event_field(struct list_head *head, char *name)
+__find_event_field(struct list_head *head, const char *name)
{
struct ftrace_event_field *field;
@@ -114,7 +114,8 @@ trace_find_event_field(struct trace_event_call *call, char *name)
static int __trace_define_field(struct list_head *head, const char *type,
const char *name, int offset, int size,
- int is_signed, int filter_type, int len)
+ int is_signed, int filter_type, int len,
+ int need_test)
{
struct ftrace_event_field *field;
@@ -133,6 +134,7 @@ static int __trace_define_field(struct list_head *head, const char *type,
field->offset = offset;
field->size = size;
field->is_signed = is_signed;
+ field->needs_test = need_test;
field->len = len;
list_add(&field->link, head);
@@ -151,13 +153,13 @@ int trace_define_field(struct trace_event_call *call, const char *type,
head = trace_get_fields(call);
return __trace_define_field(head, type, name, offset, size,
- is_signed, filter_type, 0);
+ is_signed, filter_type, 0, 0);
}
EXPORT_SYMBOL_GPL(trace_define_field);
static int trace_define_field_ext(struct trace_event_call *call, const char *type,
const char *name, int offset, int size, int is_signed,
- int filter_type, int len)
+ int filter_type, int len, int need_test)
{
struct list_head *head;
@@ -166,13 +168,13 @@ static int trace_define_field_ext(struct trace_event_call *call, const char *typ
head = trace_get_fields(call);
return __trace_define_field(head, type, name, offset, size,
- is_signed, filter_type, len);
+ is_signed, filter_type, len, need_test);
}
#define __generic_field(type, item, filter_type) \
ret = __trace_define_field(&ftrace_generic_fields, #type, \
#item, 0, 0, is_signed_type(type), \
- filter_type, 0); \
+ filter_type, 0, 0); \
if (ret) \
return ret;
@@ -181,7 +183,8 @@ static int trace_define_field_ext(struct trace_event_call *call, const char *typ
"common_" #item, \
offsetof(typeof(ent), item), \
sizeof(ent.item), \
- is_signed_type(type), FILTER_OTHER, 0); \
+ is_signed_type(type), FILTER_OTHER, \
+ 0, 0); \
if (ret) \
return ret;
@@ -332,6 +335,7 @@ static bool process_pointer(const char *fmt, int len, struct trace_event_call *c
/* Return true if the string is safe */
static bool process_string(const char *fmt, int len, struct trace_event_call *call)
{
+ struct trace_event_fields *field;
const char *r, *e, *s;
e = fmt + len;
@@ -372,8 +376,16 @@ static bool process_string(const char *fmt, int len, struct trace_event_call *ca
if (process_pointer(fmt, len, call))
return true;
- /* Make sure the field is found, and consider it OK for now if it is */
- return find_event_field(fmt, call) != NULL;
+ /* Make sure the field is found */
+ field = find_event_field(fmt, call);
+ if (!field)
+ return false;
+
+ /* Test this field's string before printing the event */
+ call->flags |= TRACE_EVENT_FL_TEST_STR;
+ field->needs_test = 1;
+
+ return true;
}
/*
@@ -2586,7 +2598,7 @@ event_define_fields(struct trace_event_call *call)
ret = trace_define_field_ext(call, field->type, field->name,
offset, field->size,
field->is_signed, field->filter_type,
- field->len);
+ field->len, field->needs_test);
if (WARN_ON_ONCE(ret)) {
pr_err("error code is %d\n", ret);
break;
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index da748b7cbc4d..03d56f711ad1 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -317,10 +317,14 @@ EXPORT_SYMBOL(trace_raw_output_prep);
void trace_event_printf(struct trace_iterator *iter, const char *fmt, ...)
{
+ struct trace_seq *s = &iter->seq;
va_list ap;
+ if (ignore_event(iter))
+ return;
+
va_start(ap, fmt);
- trace_check_vprintf(iter, trace_event_format(iter, fmt), ap);
+ trace_seq_vprintf(s, trace_event_format(iter, fmt), ap);
va_end(ap);
}
EXPORT_SYMBOL(trace_event_printf);
--
2.45.2
^ permalink raw reply related [flat|nested] 4+ messages in thread