On Wed, Apr 03, 2019 at 09:12:16PM -0700, Andy Lutomirski wrote:
> On Wed, Apr 3, 2019 at 6:42 PM Tycho Andersen <ty...@tycho.ws> wrote:
> >
> > On Wed, Apr 03, 2019 at 05:12:56PM -0700, Andy Lutomirski wrote:
> > > On Wed, Apr 3, 2019 at 10:36 AM Khalid Aziz <khalid.a...@oracle.com>
> > > wrote:
> > > >
> > > > From: Tycho Andersen <ty...@tycho.ws>
> > > >
> > > > Oopsing might kill the task, via rewind_stack_do_exit() at the bottom,
> > > > and
> > > > that might sleep:
> > > >
> > >
> > >
> > > > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> > > > index 9d5c75f02295..7891add0913f 100644
> > > > --- a/arch/x86/mm/fault.c
> > > > +++ b/arch/x86/mm/fault.c
> > > > @@ -858,6 +858,12 @@ no_context(struct pt_regs *regs, unsigned long
> > > > error_code,
> > > > /* Executive summary in case the body of the oops scrolled away
> > > > */
> > > > printk(KERN_DEFAULT "CR2: %016lx\n", address);
> > > >
> > > > + /*
> > > > + * We're about to oops, which might kill the task. Make sure
> > > > we're
> > > > + * allowed to sleep.
> > > > + */
> > > > + flags |= X86_EFLAGS_IF;
> > > > +
> > > > oops_end(flags, regs, sig);
> > > > }
> > > >
> > >
> > >
> > > NAK. If there's a bug in rewind_stack_do_exit(), please fix it in
> > > rewind_stack_do_exit().
> >
> > [I trimmed the CC list since google rejected it with E2BIG :)]
> >
> > I guess the problem is really that do_exit() (or really
> > exit_signals()) might sleep. Maybe we should put an irq_enable() at
> > the beginning of do_exit() instead and fix this problem for all
> > arches?
> >
>
> Hmm. do_exit() isn't really meant to be "try your best to leave the
> system somewhat usable without returning" -- it's a function that,
> other than in OOPSes, is called from a well-defined state. So I think
> rewind_stack_do_exit() is probably a better spot. But we need to
> rewind the stack and *then* turn on IRQs, since we otherwise risk
> exploding quite badly.
Ok, sounds good. I guess we can include something like this patch in
the next series.
Thanks,
Tycho
>From 34dce229a4f43f90db823671eb0b8da7c4906045 Mon Sep 17 00:00:00 2001
From: Tycho Andersen <ty...@tycho.ws>
Date: Thu, 4 Apr 2019 09:41:32 -0600
Subject: [PATCH] x86/entry: re-enable interrupts before exiting
If the kernel oopses in an interrupt, nothing re-enables interrupts:
Aug 23 19:30:27 xpfo kernel: [ 38.302714] BUG: sleeping function called from
invalid context at
./include/linux/percpu-rwsem.h:33
Aug 23 19:30:27 xpfo kernel: [ 38.303837] in_atomic(): 0, irqs_disabled(): 1,
pid: 1970, name:
lkdtm_xpfo_test
Aug 23 19:30:27 xpfo kernel: [ 38.304758] CPU: 3 PID: 1970 Comm:
lkdtm_xpfo_test Tainted: G D
4.13.0-rc5+ #228
Aug 23 19:30:27 xpfo kernel: [ 38.305813] Hardware name: QEMU Standard PC
(i440FX + PIIX, 1996), BIOS
1.10.1-1ubuntu1 04/01/2014
Aug 23 19:30:27 xpfo kernel: [ 38.306926] Call Trace:
Aug 23 19:30:27 xpfo kernel: [ 38.307243] dump_stack+0x63/0x8b
Aug 23 19:30:27 xpfo kernel: [ 38.307665] ___might_sleep+0xec/0x110
Aug 23 19:30:27 xpfo kernel: [ 38.308139] __might_sleep+0x45/0x80
Aug 23 19:30:27 xpfo kernel: [ 38.308593] exit_signals+0x21/0x1c0
Aug 23 19:30:27 xpfo kernel: [ 38.309046] ?
blocking_notifier_call_chain+0x11/0x20
Aug 23 19:30:27 xpfo kernel: [ 38.309677] do_exit+0x98/0xbf0
Aug 23 19:30:27 xpfo kernel: [ 38.310078] ? smp_reader+0x27/0x40 [lkdtm]
Aug 23 19:30:27 xpfo kernel: [ 38.310604] ? kthread+0x10f/0x150
Aug 23 19:30:27 xpfo kernel: [ 38.311045] ? read_user_with_flags+0x60/0x60
[lkdtm]
Aug 23 19:30:27 xpfo kernel: [ 38.311680] rewind_stack_do_exit+0x17/0x20
do_exit() expects to be called in a well-defined environment, so let's
re-enable interrupts after unwinding the stack, in case they were disabled.
Signed-off-by: Tycho Andersen <ty...@tycho.ws>
---
arch/x86/entry/entry_32.S | 6 ++++++
arch/x86/entry/entry_64.S | 6 ++++++
2 files changed, 12 insertions(+)
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index d309f30cf7af..8ddb7b41669d 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -1507,6 +1507,12 @@ ENTRY(rewind_stack_do_exit)
movl PER_CPU_VAR(cpu_current_top_of_stack), %esi
leal -TOP_OF_KERNEL_STACK_PADDING-PTREGS_SIZE(%esi), %esp
+ /*
+ * If we oopsed in an interrupt handler, interrupts may be off. Let's
turn
+ * them back on before going back to "normal" code.
+ */
+ sti
+
call do_exit
1: jmp 1b
END(rewind_stack_do_exit)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 1f0efdb7b629..c0759f3e3ad2 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1672,5 +1672,11 @@ ENTRY(rewind_stack_do_exit)
leaq -PTREGS_SIZE(%rax), %rsp
UNWIND_HINT_FUNC sp_offset=PTREGS_SIZE
+ /*
+ * If we oopsed in an interrupt handler, interrupts may be off. Let's
turn
+ * them back on before going back to "normal" code.
+ */
+ sti
+
call do_exit
END(rewind_stack_do_exit)
--
2.19.1
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