[PATCH 5.6 159/194] x86/unwind/orc: Fix error handling in __unwind_start()

Greg Kroah-Hartman
2020-05-18T18:06:35Z

From: Josh Poimboeuf <jpoimboe@redhat.com>

commit 71c95825289f585014fe9741b051d32a7a916680 upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kernel/unwind_orc.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)

--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -611,23 +611,23 @@ 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;
@@ -660,6 +660,7 @@ void __unwind_start(struct unwind_state
* 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;
@@ -685,8 +686,9 @@ void __unwind_start(struct unwind_state

return;

-done:
+err:
+ state->error = true;
+the_end:
state->stack_info.type = STACK_TYPE_UNKNOWN;
- return;
}
EXPORT_SYMBOL_GPL(__unwind_start);