x86/unwind/orc: Fix error handling in __unwind_start()

The unwind_state 'error' field is used to inform the reliable unwinding
code that the stack trace can't be trusted.  Set this field for all
errors in __unwind_start().

Also, move the zeroing out of the unwind_state struct to before the ORC
table initialization check, to prevent the caller from reading
uninitialized data if the ORC table is corrupted.

Fixes: af085d9084b4 ("stacktrace/x86: add function for detecting reliable stack traces")
Fixes: d3a09104018c ("x86/unwinder/orc: Dont bail on stack overflow")
Fixes: 98d0c8ebf77e ("x86/unwind/orc: Prevent unwinding before ORC initialization")
Reported-by: Pavel Machek <pavel@denx.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/d6ac7215a84ca92b895fdd2e1aa546729417e6e6.1589487277.git.jpoimboe@redhat.com

diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index 5b0bd85..fa79e42 100644 (file)
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -617,23 +617,23 @@ EXPORT_SYMBOL_GPL(unwind_next_frame);
 void __unwind_start(struct unwind_state *state, struct task_struct *task,
                    struct pt_regs *regs, unsigned long *first_frame)
 {
-       if (!orc_init)
-               goto done;
-
        memset(state, 0, sizeof(*state));
        state->task = task;
 
+       if (!orc_init)
+               goto err;
+
        /*
         * Refuse to unwind the stack of a task while it's executing on another
         * CPU.  This check is racy, but that's ok: the unwinder has other
         * checks to prevent it from going off the rails.
         */
        if (task_on_another_cpu(task))
-               goto done;
+               goto err;
 
        if (regs) {
                if (user_mode(regs))
-                       goto done;
+                       goto the_end;
 
                state->ip = regs->ip;
                state->sp = regs->sp;
@@ -666,6 +666,7 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
                 * generate some kind of backtrace if this happens.
                 */
                void *next_page = (void *)PAGE_ALIGN((unsigned long)state->sp);
+               state->error = true;
                if (get_stack_info(next_page, state->task, &state->stack_info,
                                   &state->stack_mask))
                        return;
@@ -691,8 +692,9 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
 
        return;
 
-done:
+err:
+       state->error = true;
+the_end:
        state->stack_info.type = STACK_TYPE_UNKNOWN;
-       return;
 }
 EXPORT_SYMBOL_GPL(__unwind_start);