From: Josh Poimboeuf <jpoimboe@redhat.com>
To: x86@kernel.org
Cc: linux-kernel@vger.kernel.org, live-patching@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Wang ShaoBo <bobo.shaobowang@huawei.com>
Subject: [PATCH 1/2] x86/unwind/orc: Fix ORC for newly forked tasks
Date: Fri, 17 Jul 2020 09:04:25 -0500 [thread overview]
Message-ID: <f91a8778dde8aae7f71884b5df2b16d552040441.1594994374.git.jpoimboe@redhat.com> (raw)
In-Reply-To: <cover.1594994374.git.jpoimboe@redhat.com>
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 <bobo.shaobowang@huawei.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
arch/x86/kernel/unwind_orc.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index 7f969b2d240f..ec88bbe08a32 100644
--- 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,
--
2.25.4
next prev parent reply other threads:[~2020-07-17 14:04 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-17 14:04 [PATCH 0/2] x86/unwind: A couple of fixes for newly forked tasks Josh Poimboeuf
2020-07-17 14:04 ` Josh Poimboeuf [this message]
2020-07-17 14:04 ` [PATCH 2/2] x86/stacktrace: Fix reliable check for empty user task stacks Josh Poimboeuf
2020-07-20 11:06 ` [PATCH 0/2] x86/unwind: A couple of fixes for newly forked tasks Wangshaobo (bobo)
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