[PATCH] Add sicode to /proc/<PID>/stat.

From: Florian Mayer
Date: Thu Aug 11 2022 - 13:43:54 EST

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In order to enable additional debugging features, Android init needs a
way to distinguish MTE-related SEGVs (with si_code of SEGV_MTEAERR)
from other SEGVs. This is not possible with current APIs, neither by
the existing information in /proc/<pid>/stat, nor via waitpid.

Tested with the following program

int main(int argc, char** argv) {
int pid = fork();
if (!pid) {
if (strcmp(argv[1], "sigqueue") == 0) {
union sigval value;
value.sival_int = 0;
sigqueue(getpid(), SIGSEGV, value);
} else if (strcmp(argv[1], "raise") == 0) {
raise(SIGSEGV);
} else if (strcmp(argv[1], "kill") == 0) {
kill(getpid(), SIGSEGV);
} else if (strcmp(argv[1], "raisestop") == 0) {
raise(SIGSTOP);
} else if (strcmp(argv[1], "crash") == 0) {
volatile int* x = (int*)(0x23);
*x = 1;
} else if (strcmp(argv[1], "mte") == 0) {
volatile char* y = malloc(1);
y += 100;
*y = 1;
}
} else {
printf("%d\n", pid);
sleep(5);
char buf[1024];
sprintf(buf, "/proc/%d/stat", pid);
int fd = open(buf, O_RDONLY);
char statb[1024];
read(fd, statb, sizeof(statb));
printf("%s\n", statb);
}
}

Signed-off-by: Florian Mayer <fmayer@xxxxxxxxxx>
---
Documentation/filesystems/proc.rst | 2 ++
fs/coredump.c | 17 ++++++++++-------
fs/proc/array.c | 12 ++++++++----
include/linux/sched/signal.h | 1 +
include/linux/sched/task.h | 2 +-
kernel/exit.c | 5 +++--
kernel/pid_namespace.c | 4 +++-
kernel/signal.c | 29 +++++++++++++++++++----------
8 files changed, 47 insertions(+), 25 deletions(-)

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index e7aafc82be99..12ad5ecd7434 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -381,6 +381,8 @@ It's slow but very precise.
env_end address below which program environment is placed
exit_code the thread's exit_code in the form reported by the waitpid
system call
+ exit_sicode if the process was stopped or terminated by a signal, the
+ signal's si_code. 0 otherwise
============= ===============================================================

The /proc/PID/maps file contains the currently mapped memory regions and
diff --git a/fs/coredump.c b/fs/coredump.c
index 9f4aae202109..61e9f27d2bf8 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -349,7 +349,7 @@ static int format_corename(struct core_name *cn, struct coredump_params *cprm,
return ispipe;
}

-static int zap_process(struct task_struct *start, int exit_code)
+static int zap_process(struct task_struct *start, int exit_code, int sicode)
{
struct task_struct *t;
int nr = 0;
@@ -357,6 +357,7 @@ static int zap_process(struct task_struct *start, int exit_code)
/* ignore all signals except SIGKILL, see prepare_signal() */
start->signal->flags = SIGNAL_GROUP_EXIT;
start->signal->group_exit_code = exit_code;
+ start->signal->group_exit_sicode = sicode;
start->signal->group_stop_count = 0;

for_each_thread(start, t) {
@@ -371,8 +372,8 @@ static int zap_process(struct task_struct *start, int exit_code)
return nr;
}

-static int zap_threads(struct task_struct *tsk,
- struct core_state *core_state, int exit_code)
+static int zap_threads(struct task_struct *tsk, struct core_state *core_state,
+ int exit_code, int sicode)
{
struct signal_struct *signal = tsk->signal;
int nr = -EAGAIN;
@@ -380,7 +381,7 @@ static int zap_threads(struct task_struct *tsk,
spin_lock_irq(&tsk->sighand->siglock);
if (!(signal->flags & SIGNAL_GROUP_EXIT) && !signal->group_exec_task) {
signal->core_state = core_state;
- nr = zap_process(tsk, exit_code);
+ nr = zap_process(tsk, exit_code, sicode);
clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
tsk->flags |= PF_DUMPCORE;
atomic_set(&core_state->nr_threads, nr);
@@ -389,7 +390,8 @@ static int zap_threads(struct task_struct *tsk,
return nr;
}

-static int coredump_wait(int exit_code, struct core_state *core_state)
+static int coredump_wait(int exit_code, int sicode,
+ struct core_state *core_state)
{
struct task_struct *tsk = current;
int core_waiters = -EBUSY;
@@ -398,7 +400,7 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
core_state->dumper.task = tsk;
core_state->dumper.next = NULL;

- core_waiters = zap_threads(tsk, core_state, exit_code);
+ core_waiters = zap_threads(tsk, core_state, exit_code, sicode);
if (core_waiters > 0) {
struct core_thread *ptr;

@@ -560,7 +562,8 @@ void do_coredump(const kernel_siginfo_t *siginfo)
need_suid_safe = true;
}

- retval = coredump_wait(siginfo->si_signo, &core_state);
+ retval =
+ coredump_wait(siginfo->si_signo, siginfo->si_code, &core_state);
if (retval < 0)
goto fail_creds;

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 99fcbfda8e25..23553460627c 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -474,6 +474,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
unsigned long rsslim = 0;
unsigned long flags;
int exit_code = task->exit_code;
+ int exit_sicode = 0;

state = *get_task_state(task);
vsize = eip = esp = 0;
@@ -538,8 +539,10 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
thread_group_cputime_adjusted(task, &utime, &stime);
gtime += sig->gtime;

- if (sig->flags & (SIGNAL_GROUP_EXIT | SIGNAL_STOP_STOPPED))
+ if (sig->flags & (SIGNAL_GROUP_EXIT | SIGNAL_STOP_STOPPED)) {
exit_code = sig->group_exit_code;
+ exit_sicode = sig->group_exit_sicode;
+ }
}

sid = task_session_nr_ns(task, ns);
@@ -638,10 +641,11 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
} else
seq_puts(m, " 0 0 0 0 0 0 0");

- if (permitted)
+ if (permitted) {
seq_put_decimal_ll(m, " ", exit_code);
- else
- seq_puts(m, " 0");
+ seq_put_decimal_ll(m, " ", exit_sicode);
+ } else
+ seq_puts(m, " 0 0");

seq_putc(m, '\n');
if (mm)
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index cafbe03eed01..1631dba7a7db 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -109,6 +109,7 @@ struct signal_struct {

/* thread group exit support */
int group_exit_code;
+ int group_exit_sicode;
/* notify group_exec_task when notify_count is less or equal to 0 */
int notify_count;
struct task_struct *group_exec_task;
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 81cab4b01edc..6ff4825fc88a 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -82,7 +82,7 @@ static inline void exit_thread(struct task_struct *tsk)
{
}
#endif
-extern __noreturn void do_group_exit(int);
+extern __noreturn void do_group_exit(int,int);

extern void exit_files(struct task_struct *);
extern void exit_itimers(struct task_struct *);
diff --git a/kernel/exit.c b/kernel/exit.c
index 84021b24f79e..278469d13433 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -897,7 +897,7 @@ SYSCALL_DEFINE1(exit, int, error_code)
* as well as by sys_exit_group (below).
*/
void __noreturn
-do_group_exit(int exit_code)
+do_group_exit(int exit_code, int sicode)
{
struct signal_struct *sig = current->signal;

@@ -916,6 +916,7 @@ do_group_exit(int exit_code)
exit_code = 0;
else {
sig->group_exit_code = exit_code;
+ sig->group_exit_sicode = sicode;
sig->flags = SIGNAL_GROUP_EXIT;
zap_other_threads(current);
}
@@ -933,7 +934,7 @@ do_group_exit(int exit_code)
*/
SYSCALL_DEFINE1(exit_group, int, error_code)
{
- do_group_exit((error_code & 0xff) << 8);
+ do_group_exit((error_code & 0xff) << 8, 0);
/* NOTREACHED */
return 0;
}
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index f4f8cb0435b4..c80db136726d 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -248,8 +248,10 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
}
__set_current_state(TASK_RUNNING);

- if (pid_ns->reboot)
+ if (pid_ns->reboot) {
current->signal->group_exit_code = pid_ns->reboot;
+ current->signal->group_exit_sicode = 0;
+ }

acct_exit_ns(pid_ns);
return;
diff --git a/kernel/signal.c b/kernel/signal.c
index 6f86fda5e432..180310a9171c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -963,6 +963,7 @@ static bool prepare_signal(int sig, struct task_struct *p, bool force)
signal_set_stop_flags(signal, why | SIGNAL_STOP_CONTINUED);
signal->group_stop_count = 0;
signal->group_exit_code = 0;
+ signal->group_exit_sicode = 0;
}
}

@@ -994,7 +995,8 @@ static inline bool wants_signal(int sig, struct task_struct *p)
return task_curr(p) || !task_sigpending(p);
}

-static void complete_signal(int sig, struct task_struct *p, enum pid_type type)
+static void complete_signal(int sig, int code, struct task_struct *p,
+ enum pid_type type)
{
struct signal_struct *signal = p->signal;
struct task_struct *t;
@@ -1051,6 +1053,7 @@ static void complete_signal(int sig, struct task_struct *p, enum pid_type type)
*/
signal->flags = SIGNAL_GROUP_EXIT;
signal->group_exit_code = sig;
+ signal->group_exit_sicode = code;
signal->group_stop_count = 0;
t = p;
do {
@@ -1082,6 +1085,7 @@ static int __send_signal_locked(int sig, struct kernel_siginfo *info,
struct sigqueue *q;
int override_rlimit;
int ret = 0, result;
+ int code = 0;

lockdep_assert_held(&t->sighand->siglock);

@@ -1129,7 +1133,7 @@ static int __send_signal_locked(int sig, struct kernel_siginfo *info,
clear_siginfo(&q->info);
q->info.si_signo = sig;
q->info.si_errno = 0;
- q->info.si_code = SI_USER;
+ code = q->info.si_code = SI_USER;
q->info.si_pid = task_tgid_nr_ns(current,
task_active_pid_ns(t));
rcu_read_lock();
@@ -1142,12 +1146,13 @@ static int __send_signal_locked(int sig, struct kernel_siginfo *info,
clear_siginfo(&q->info);
q->info.si_signo = sig;
q->info.si_errno = 0;
- q->info.si_code = SI_KERNEL;
+ code = q->info.si_code = SI_KERNEL;
q->info.si_pid = 0;
q->info.si_uid = 0;
break;
default:
copy_siginfo(&q->info, info);
+ code = info->si_code;
break;
}
} else if (!is_si_special(info) &&
@@ -1186,7 +1191,7 @@ static int __send_signal_locked(int sig, struct kernel_siginfo *info,
}
}

- complete_signal(sig, t, type);
+ complete_signal(sig, code, t, type);
ret:
trace_signal_generate(sig, info, t, type != PIDTYPE_PID, result);
return ret;
@@ -1960,6 +1965,7 @@ void sigqueue_free(struct sigqueue *q)
int send_sigqueue(struct sigqueue *q, struct pid *pid, enum pid_type type)
{
int sig = q->info.si_signo;
+ int code = q->info.si_code;
struct sigpending *pending;
struct task_struct *t;
unsigned long flags;
@@ -1995,7 +2001,7 @@ int send_sigqueue(struct sigqueue *q, struct pid *pid, enum pid_type type)
pending = (type != PIDTYPE_PID) ? &t->signal->shared_pending : &t->pending;
list_add_tail(&q->list, &pending->list);
sigaddset(&pending->signal, sig);
- complete_signal(sig, t, type);
+ complete_signal(sig, code, t, type);
result = TRACE_SIGNAL_DELIVERED;
out:
trace_signal_generate(sig, &q->info, t, type != PIDTYPE_PID, result);
@@ -2380,7 +2386,7 @@ int ptrace_notify(int exit_code, unsigned long message)
* %false if group stop is already cancelled or ptrace trap is scheduled.
* %true if participated in group stop.
*/
-static bool do_signal_stop(int signr)
+static bool do_signal_stop(int signr, int sicode)
__releases(&current->sighand->siglock)
{
struct signal_struct *sig = current->signal;
@@ -2415,8 +2421,10 @@ static bool do_signal_stop(int signr)
* an intervening stop signal is required to cause two
* continued events regardless of ptrace.
*/
- if (!(sig->flags & SIGNAL_STOP_STOPPED))
+ if (!(sig->flags & SIGNAL_STOP_STOPPED)) {
sig->group_exit_code = signr;
+ sig->group_exit_sicode = sicode;
+ }

sig->group_stop_count = 0;

@@ -2701,7 +2709,7 @@ bool get_signal(struct ksignal *ksig)
}

if (unlikely(current->jobctl & JOBCTL_STOP_PENDING) &&
- do_signal_stop(0))
+ do_signal_stop(0, 0))
goto relock;

if (unlikely(current->jobctl &
@@ -2806,7 +2814,8 @@ bool get_signal(struct ksignal *ksig)
spin_lock_irq(&sighand->siglock);
}

- if (likely(do_signal_stop(ksig->info.si_signo))) {
+ if (likely(do_signal_stop(ksig->info.si_signo,
+ ksig->info.si_code))) {
/* It released the siglock. */
goto relock;
}
@@ -2854,7 +2863,7 @@ bool get_signal(struct ksignal *ksig)
/*
* Death signals, no core dump.
*/
- do_group_exit(ksig->info.si_signo);
+ do_group_exit(ksig->info.si_signo, ksig->info.si_code);
/* NOTREACHED */
}
spin_unlock_irq(&sighand->siglock);
--
2.37.1.559.g78731f0fdb-goog

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