[signal] Handle corner case: setting up user stack faults

vvaltchev · Jun 12, 2022 · 0a3159d · 0a3159d
1 parent e7df2c4
commit 0a3159d
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Showing 3 changed files with 26 additions and 17 deletions.
diff --git a/include/tilck/kernel/process.h b/include/tilck/kernel/process.h
@@ -149,9 +149,9 @@ void process_set_cwd2_nolock(struct vfs_path *tp);
 void process_set_cwd2_nolock_raw(struct process *pi, struct vfs_path *tp);
 void terminate_process(int exit_code, int term_sig);
 void close_cloexec_handles(struct process *pi);
-void setup_sig_handler(struct task *ti,
-                       enum sig_state sig_state,
-                       regs_t *r,
-                       ulong user_func,
-                       int signum);
+int setup_sig_handler(struct task *ti,
+                      enum sig_state sig_state,
+                      regs_t *r,
+                      ulong user_func,
+                      int signum);
 void setup_pause_trampoline(regs_t *r);
diff --git a/kernel/arch/i386/process32.c b/kernel/arch/i386/process32.c
@@ -140,7 +140,7 @@ push_args_on_user_stack(regs_t *r,
    return 0;
 }
 
-static void save_regs_on_user_stack(regs_t *r)
+static int save_regs_on_user_stack(regs_t *r)
 {
    ulong new_useresp = r->useresp;
    int rc;
@@ -155,14 +155,13 @@ static void save_regs_on_user_stack(regs_t *r)
    rc = copy_to_user(TO_PTR(new_useresp), r, sizeof(*r));
 
    if (rc) {
-      /* Oops, stack overflow: terminate the process */
-      enable_preemption();
-      terminate_process(0, SIGSEGV);
-      NOT_REACHED();
+      /* Oops, stack overflow */
+      return -EFAULT;
    }
 
    /* Now, after we saved the registers, update r->useresp */
    r->useresp = new_useresp;
+   return 0;
 }
 
 static void restore_regs_from_user_stack(regs_t *r)
@@ -200,18 +199,21 @@ void setup_pause_trampoline(regs_t *r)
       ) % USERMODE_STACK_ALIGN                          \
    )
 
-void setup_sig_handler(struct task *ti,
-                       enum sig_state sig_state,
-                       regs_t *r,
-                       ulong user_func,
-                       int signum)
+int setup_sig_handler(struct task *ti,
+                      enum sig_state sig_state,
+                      regs_t *r,
+                      ulong user_func,
+                      int signum)
 {
    if (ti->nested_sig_handlers == 0) {
 
+      int rc;
+
       if (sig_state == sig_pre_syscall)
          r->eax = (ulong) -EINTR;
 
-      save_regs_on_user_stack(r);
+      if ((rc = save_regs_on_user_stack(r)) < 0)
+         return rc;
    }
 
    r->eip = user_func;
@@ -233,6 +235,7 @@ void setup_sig_handler(struct task *ti,
     *    0xbfffce20             # it's already aligned at 16
     */
    ASSERT(((r->useresp + sizeof(ulong)) & (USERMODE_STACK_ALIGN - 1)) == 0);
+   return 0;
 }
 
 ulong sys_rt_sigreturn(void)

diff --git a/kernel/signal.c b/kernel/signal.c
@@ -194,7 +194,13 @@ bool process_signals(void *__ti, enum sig_state sig_state, void *regs)
                    handler, ti->tid, get_signal_name(sig), sig);
 
       del_pending_sig(ti, sig);
-      setup_sig_handler(ti, sig_state, regs, (ulong)handler, sig);
+
+      if (setup_sig_handler(ti, sig_state, regs, (ulong)handler, sig) < 0) {
+
+         /* We got a FAULT while trying to setup the user stack */
+         printk("WARNING: can't setup stack for task %d: kill\n", ti->tid);
+         kill_task_now_or_later(ti, regs, SIGKILL, sig_state);
+      }
 
    } else {