x86/unwind/orc: Fix ORC for newly forked tasks

The ORC unwinder fails to unwind newly forked tasks which haven't yet run on the CPU. It correctly reads the 'ret_from_fork' instruction pointer from the stack, but it incorrectly interprets that value as a call stack address rather than a "signal" one, so the address gets incorrectly decremented in the call to orc_find(), resulting in bad ORC data. Fix it by forcing 'ret_from_fork' frames to be signal frames. Reported-by: Wang ShaoBo <[email protected]> Signed-off-by: Josh Poimboeuf <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Tested-by: Wang ShaoBo <[email protected]> Link: https://lkml.kernel.org/r/f91a8778dde8aae7f71884b5df2b16d552040441.1594994374.git.jpoimboe@redhat.com
devinus · Jul 22, 2020 · 372a8ea · 372a8ea
1 parent de2b41b
commit 372a8ea
Showing 1 changed file with 6 additions and 2 deletions.
diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
@@ -440,8 +440,11 @@ bool unwind_next_frame(struct unwind_state *state)
 	/*
 	 * Find the orc_entry associated with the text address.
 	 *
-	 * Decrement call return addresses by one so they work for sibling
-	 * calls and calls to noreturn functions.
+	 * For a call frame (as opposed to a signal frame), state->ip points to
+	 * the instruction after the call.  That instruction's stack layout
+	 * could be different from the call instruction's layout, for example
+	 * if the call was to a noreturn function.  So get the ORC data for the
+	 * call instruction itself.
 	 */
 	orc = orc_find(state->signal ? state->ip : state->ip - 1);
 	if (!orc) {
@@ -662,6 +665,7 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
 		state->sp = task->thread.sp;
 		state->bp = READ_ONCE_NOCHECK(frame->bp);
 		state->ip = READ_ONCE_NOCHECK(frame->ret_addr);
+		state->signal = (void *)state->ip == ret_from_fork;
 	}
 
 	if (get_stack_info((unsigned long *)state->sp, state->task,