[PATCH AUTOSEL 4.19 08/10] x86/unwind/orc: Fix ORC for newly forked tasks

From: Sasha Levin
Date: Mon Jul 27 2020 - 19:27:13 EST

From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

[ Upstream commit 372a8eaa05998cd45b3417d0e0ffd3a70978211a ]

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

Fix it by forcing 'ret_from_fork' frames to be signal frames.

Reported-by: Wang ShaoBo <bobo.shaobowang@xxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Wang ShaoBo <bobo.shaobowang@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/f91a8778dde8aae7f71884b5df2b16d552040441.1594994374.git.jpoimboe@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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 2701b370e58fe..1d264ba1e56d1 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -420,8 +420,11 @@ 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)
@@ -634,6 +637,7 @@ 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,