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tracing: Have system call events record user array data

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For system call events that have a length field, add a "user_arg_size"
parameter to the system call meta data that denotes the index of the args
array that holds the size of arg that the user_mask field has a bit set
for.

The "user_mask" has a bit set that denotes the arg that points to an array
in the user space address space and if a system call event has the
user_mask field set and the user_arg_size set, it will then record the
content of that address into the trace event, up to the size defined by
SYSCALL_FAULT_BUF_SZ - 1.

This allows the output to look like:

  sys_write(fd: 0xa, buf: 0x5646978d13c0 (01:00:05:00:00:00:00:00:01:87:55:89:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00), count: 0x20)

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: Peter Zijlstra <peterz@infradead.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Takaya Saeki <takayas@google.com>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ian Rogers <irogers@google.com>
Cc: Douglas Raillard <douglas.raillard@arm.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Link: https://lore.kernel.org/20251028231147.763528474@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2025-10-28 19:11:19 -04:00 committed by Steven Rostedt (Google)
parent 2e82e256df
commit b4f7624cfc
2 changed files with 90 additions and 35 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/trace/syscall.h
View File

@ -16,6 +16,7 @@
* @name: name of the syscall
* @syscall_nr: number of the syscall
* @nb_args: number of parameters it takes
* @user_arg_size: holds @arg that has size of the user space to read
* @user_mask: mask of @args that will read user space
* @types: list of types as strings
* @args: list of args as strings (args[i] matches types[i])
@ -26,7 +27,8 @@
struct syscall_metadata {
const char *name;
int syscall_nr;
short nb_args;
u8 nb_args;
s8 user_arg_size;
short user_mask;
const char **types;
const char **args;

121
kernel/trace/trace_syscalls.c
View File

@ -124,7 +124,7 @@ const char *get_syscall_name(int syscall)
return entry->name;
}
/* Added to user strings when max limit is reached */
/* Added to user strings or arrays when max limit is reached */
#define EXTRA "..."
static enum print_line_t
@ -136,9 +136,8 @@ print_syscall_enter(struct trace_iterator *iter, int flags,
struct trace_entry *ent = iter->ent;
struct syscall_trace_enter *trace;
struct syscall_metadata *entry;
int i, syscall, val;
int i, syscall, val, len;
unsigned char *ptr;
int len;
trace = (typeof(trace))ent;
syscall = trace->nr;
@ -185,7 +184,23 @@ print_syscall_enter(struct trace_iterator *iter, int flags,
ptr = (void *)ent + (val & 0xffff);
len = val >> 16;
trace_seq_printf(s, " \"%.*s\"", len, ptr);
if (entry->user_arg_size < 0) {
trace_seq_printf(s, " \"%.*s\"", len, ptr);
continue;
}
val = trace->args[entry->user_arg_size];
trace_seq_puts(s, " (");
for (int x = 0; x < len; x++, ptr++) {
if (x)
trace_seq_putc(s, ':');
trace_seq_printf(s, "%02x", *ptr);
}
if (len < val)
trace_seq_printf(s, ", %s", EXTRA);
trace_seq_putc(s, ')');
}
trace_seq_putc(s, ')');
@ -250,8 +265,11 @@ __set_enter_print_fmt(struct syscall_metadata *entry, char *buf, int len)
if (!(BIT(i) & entry->user_mask))
continue;
/* Add the format for the user space string */
pos += snprintf(buf + pos, LEN_OR_ZERO, " \\\"%%s\\\"");
/* Add the format for the user space string or array */
if (entry->user_arg_size < 0)
pos += snprintf(buf + pos, LEN_OR_ZERO, " \\\"%%s\\\"");
else
pos += snprintf(buf + pos, LEN_OR_ZERO, " (%%s)");
}
pos += snprintf(buf + pos, LEN_OR_ZERO, "\"");
@ -260,9 +278,14 @@ __set_enter_print_fmt(struct syscall_metadata *entry, char *buf, int len)
", ((unsigned long)(REC->%s))", entry->args[i]);
if (!(BIT(i) & entry->user_mask))
continue;
/* The user space string for arg has name __<arg>_val */
pos += snprintf(buf + pos, LEN_OR_ZERO, ", __get_str(__%s_val)",
entry->args[i]);
/* The user space data for arg has name __<arg>_val */
if (entry->user_arg_size < 0) {
pos += snprintf(buf + pos, LEN_OR_ZERO, ", __get_str(__%s_val)",
entry->args[i]);
} else {
pos += snprintf(buf + pos, LEN_OR_ZERO, ", __print_dynamic_array(__%s_val, 1)",
entry->args[i]);
}
}
#undef LEN_OR_ZERO
@ -333,9 +356,9 @@ static int __init syscall_enter_define_fields(struct trace_event_call *call)
idx = ffs(mask) - 1;
/*
* User space strings are faulted into a temporary buffer and then
* added as a dynamic string to the end of the event.
* The user space string name for the arg pointer is "__<arg>_val".
* User space data is faulted into a temporary buffer and then
* added as a dynamic string or array to the end of the event.
* The user space data name for the arg pointer is "__<arg>_val".
*/
len = strlen(meta->args[idx]) + sizeof("___val");
arg = kmalloc(len, GFP_KERNEL);
@ -431,9 +454,11 @@ static char *sys_fault_user(struct syscall_metadata *sys_data,
struct syscall_user_buffer *sbuf,
unsigned long *args, unsigned int *data_size)
{
trace_user_buf_copy syscall_copy = syscall_copy_user;
unsigned long size = SYSCALL_FAULT_BUF_SZ - 1;
unsigned long mask = sys_data->user_mask;
int idx = ffs(mask) - 1;
bool array = false;
char *ptr;
char *buf;
@ -441,27 +466,43 @@ static char *sys_fault_user(struct syscall_metadata *sys_data,
ptr = (char *)args[idx];
*data_size = 0;
/*
* If this system call event has a size argument, use
* it to define how much of user space memory to read,
* and read it as an array and not a string.
*/
if (sys_data->user_arg_size >= 0) {
array = true;
size = args[sys_data->user_arg_size];
if (size > SYSCALL_FAULT_BUF_SZ - 1)
size = SYSCALL_FAULT_BUF_SZ - 1;
/* use normal copy_from_user() */
syscall_copy = NULL;
}
buf = trace_user_fault_read(&sbuf->buf, ptr, size,
syscall_copy_user, &size);
syscall_copy, &size);
if (!buf)
return NULL;
/* Replace any non-printable characters with '.' */
for (int i = 0; i < size; i++) {
if (!isprint(buf[i]))
buf[i] = '.';
}
/* For strings, replace any non-printable characters with '.' */
if (!array) {
for (int i = 0; i < size; i++) {
if (!isprint(buf[i]))
buf[i] = '.';
}
/*
* If the text was truncated due to our max limit, add "..." to
* the string.
*/
if (size > SYSCALL_FAULT_BUF_SZ - sizeof(EXTRA)) {
strscpy(buf + SYSCALL_FAULT_BUF_SZ - sizeof(EXTRA),
EXTRA, sizeof(EXTRA));
size = SYSCALL_FAULT_BUF_SZ;
} else {
buf[size++] = '\0';
/*
* If the text was truncated due to our max limit, add "..." to
* the string.
*/
if (size > SYSCALL_FAULT_BUF_SZ - sizeof(EXTRA)) {
strscpy(buf + SYSCALL_FAULT_BUF_SZ - sizeof(EXTRA),
EXTRA, sizeof(EXTRA));
size = SYSCALL_FAULT_BUF_SZ;
} else {
buf[size++] = '\0';
}
}
*data_size = size;
@ -492,7 +533,7 @@ syscall_get_data(struct syscall_metadata *sys_data, unsigned long *args,
static void syscall_put_data(struct syscall_metadata *sys_data,
struct syscall_trace_enter *entry,
char *buffer, int size)
char *buffer, int size, int user_size)
{
void *ptr;
int val;
@ -510,13 +551,16 @@ static void syscall_put_data(struct syscall_metadata *sys_data,
val = (ptr - (void *)entry) + 4;
/* Store the offset and the size into the meta data */
*(int *)ptr = val | (size << 16);
*(int *)ptr = val | (user_size << 16);
if (WARN_ON_ONCE((ptr - (void *)entry + user_size) > size))
user_size = 0;
/* Nothing to do if the user space was empty or faulted */
if (size) {
if (user_size) {
/* Now store the user space data into the event */
ptr += 4;
memcpy(ptr, buffer, size);
memcpy(ptr, buffer, user_size);
}
}
@ -580,7 +624,7 @@ static void ftrace_syscall_enter(void *data, struct pt_regs *regs, long id)
memcpy(entry->args, args, sizeof(unsigned long) * sys_data->nb_args);
if (mayfault)
syscall_put_data(sys_data, entry, user_ptr, user_size);
syscall_put_data(sys_data, entry, user_ptr, size, user_size);
trace_event_buffer_commit(&fbuffer);
}
@ -727,7 +771,16 @@ static void check_faultable_syscall(struct trace_event_call *call, int nr)
if (sys_data->enter_event != call)
return;
sys_data->user_arg_size = -1;
switch (nr) {
/* user arg 1 with size arg at 2 */
case __NR_write:
case __NR_mq_timedsend:
case __NR_pwrite64:
sys_data->user_mask = BIT(1);
sys_data->user_arg_size = 2;
break;
/* user arg at position 0 */
#ifdef __NR_access
case __NR_access:
@ -1065,7 +1118,7 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
memcpy(&rec->args, args, sizeof(unsigned long) * sys_data->nb_args);
if (mayfault)
syscall_put_data(sys_data, rec, user_ptr, user_size);
syscall_put_data(sys_data, rec, user_ptr, size, user_size);
if ((valid_prog_array &&
!perf_call_bpf_enter(sys_data->enter_event, fake_regs, sys_data, rec)) ||