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Date:   Sat, 25 Nov 2017 22:48:50 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>,
        Borislav Petkov <bpetkov@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86/orc: Don't bail on stack overflow

On Sat, Nov 25, 2017 at 10:41:15PM -0600, Josh Poimboeuf wrote:
> On Sat, Nov 25, 2017 at 08:25:12PM -0800, Andy Lutomirski wrote:
> > On Sat, Nov 25, 2017 at 6:40 PM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > > On Sat, Nov 25, 2017 at 04:16:23PM -0800, Andy Lutomirski wrote:
> > >> Can you send me whatever config and exact commit hash generated this?
> > >> I can try to figure out why it failed.
> > >
> > > Sorry, I've been traveling.  I just got some time to take a look at
> > > this.  I think there are at least two unwinder issues here:
> > >
> > > - It doesn't deal gracefully with the case where the stack overflows and
> > >   the stack pointer itself isn't on a valid stack but the
> > >   to-be-dereferenced data *is*.
> > >
> > > - The oops dump code doesn't know how to print partial pt_regs, for the
> > >   case where if we get an interrupt/exception in *early* entry code
> > >   before the full pt_regs have been saved.
> > >
> > > (Andy, I'm not quite sure about your patch, and whether it's still
> > > needed after these patches.  I'll need to look at it later when I have
> > > more time.)
> > 
> > I haven't tested yet, but I think my patch is probably still needed.
> > The issue I fixed is that unwind_start() would bail out early if sp
> > was below the stack.  Also:
> 
> Makes sense, maybe both are needed.  Your patch deals with a bad SP at
> the beginning and mine deals with a bad SP in the middle.

I was able to recreate with the config Ingo posted earlier, along with
the following patch:

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index e12168936d3f..693a20d309e3 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -500,7 +500,7 @@
                VMLINUX_SYMBOL(__entry_text_end) = .;

 #define IRQENTRY_TEXT                                                  \
-               ALIGN_FUNCTION();                                       \
+               . = ALIGN(4096);                                        \
                VMLINUX_SYMBOL(__irqentry_text_start) = .;              \
                *(.irqentry.text)                                       \
                VMLINUX_SYMBOL(__irqentry_text_end) = .;


It looks a *lot* better with mine and your patches applied.  It probably
would have helped Ingo and Thomas figure the problem out a lot sooner:

[    1.159016] PANIC: double fault, error_code: 0x0
[    1.159583] CPU: 1 PID: 68 Comm: modprobe Not tainted 4.14.0-01257-g761d390195b6-dirty #19
[    1.159583] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1.fc26 04/01/2014
[    1.159583] task: ffff880136f6bb00 task.stack: ffffc90000984000
[    1.159583] RIP: 0010:page_fault+0x11/0x60
[    1.159583] RSP: 0000:ffffffffff083fc8 EFLAGS: 00010046
[    1.159583] RAX: 00000000819d0a87 RBX: 0000000000000001 RCX: ffffffff819d0a87
[    1.159583] RDX: 0000000000001000 RSI: 0000000000000010 RDI: ffffffffff084078
[    1.159583] RBP: 0000000000000d68 R08: 00007f6d6bb24278 R09: 0000000000000023
[    1.159583] R10: 0000558e0feca600 R11: 0000000000000246 R12: 00007f6d6bb203c0
[    1.159583] R13: 00007f6d6bb1f880 R14: 00007ffff793bebc R15: 0000000000000100
[    1.159583] FS:  00007f6d6c39c5c0(0000) GS:ffff88013fc40000(0000) knlGS:0000000000000000
[    1.159583] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    1.159583] CR2: ffffffffff083fb8 CR3: 0000000136f78002 CR4: 00000000001606e0
[    1.159583] Call Trace:
[    1.159583]  <SYSENTER>
[    1.159583]  __do_page_fault+0x4b0/0x4b0
[    1.159583]  page_fault+0x2c/0x60
[    1.159583] RIP: 0010:do_page_fault+0x0/0x100
[    1.159583] RSP: 0000:ffffffffff084120 EFLAGS: 00010012
[    1.159583] RAX: 00000000819d0a87 RBX: 0000000000000001 RCX: ffffffff819d0a87
[    1.159583] RDX: 0000000000001000 RSI: 0000000000000010 RDI: ffffffffff084128
[    1.159583] RBP: 0000000000000d68 R08: 00007f6d6bb24278 R09: 0000000000000023
[    1.159583] R10: 0000558e0feca600 R11: 0000000000000246 R12: 00007f6d6bb203c0
[    1.159583] R13: 00007f6d6bb1f880 R14: 00007ffff793bebc R15: 0000000000000100
[    1.159583]  ? native_iret+0x7/0x7
[    1.159583]  page_fault+0x2c/0x60
[    1.159583] RIP: 0010:apic_timer_interrupt+0x0/0xb0
[    1.159583] RSP: 0000:ffffffffff0841d8 EFLAGS: 00010046
[    1.159583] RAX: 0000000000000374 RBX: 0000558e0feca2c0 RCX: 00007f6d6b85aaf0
[    1.159583] RDX: 0000000000001000 RSI: 0000558e0feca600 RDI: 0000000000000000
[    1.159583] RBP: 0000000000000d68 R08: 00007f6d6bb24278 R09: 0000000000000023
[    1.159583] R10: 0000558e0feca600 R11: 0000000000000246 R12: 00007f6d6bb203c0
[    1.159583] R13: 00007f6d6bb1f880 R14: 00007ffff793bebc R15: 0000000000000100
[    1.159583] RIP: 0033:0x7f6d6b85aaf0
[    1.159583] RSP: 002b:00007ffff793bd68 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
[    1.159583] RAX: ffffffff819d2000 RBX: 00007f6d6b85aaf0 RCX: 0000000000000010
[    1.159583] RDX: 0000000000010046 RSI: ffffffffff0841d8 RDI: 0000000000000000
[    1.159583] RBP: 0000000000000374 R08: ffffffffffffffff R09: 0000000000000000
[    1.159583] R10: 0000558e0feca600 R11: 0000000000001000 R12: 00007f6d6bb24278
[    1.159583] R13: 0000000000000023 R14: 0000558e0feca600 R15: 0000000000000246
[    1.159583]  </SYSENTER>
[    1.159583] Code: ff e8 94 b7 6a ff e9 9f 02 00 00 0f 1f 44 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 83 c4 88 f6 84 24 88 00 00 00 03 75 20 <e8> 4a 01 00 00 48 89 e7 48 8b 74 24 78 48 c7 44 24 78 ff ff ff
[    1.159583] Kernel panic - not syncing: Machine halted.
[    1.159583] CPU: 1 PID: 68 Comm: modprobe Not tainted 4.14.0-01257-g761d390195b6-dirty #19
[    1.159583] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1.fc26 04/01/2014
[    1.159583] Call Trace:
[    1.159583]  <#DF>
[    1.159583]  dump_stack+0x46/0x59
[    1.159583]  panic+0xde/0x223
[    1.159583]  df_debug+0x29/0x30
[    1.159583]  do_double_fault+0x9a/0x120
[    1.159583]  double_fault+0x22/0x30
[    1.159583] RIP: 0010:page_fault+0x11/0x60
[    1.159583] RSP: 0000:ffffffffff083fc8 EFLAGS: 00010046
[    1.159583] RAX: 00000000819d0a87 RBX: 0000000000000001 RCX: ffffffff819d0a87
[    1.159583] RDX: 0000000000001000 RSI: 0000000000000010 RDI: ffffffffff084078
[    1.159583] RBP: 0000000000000d68 R08: 00007f6d6bb24278 R09: 0000000000000023
[    1.159583] R10: 0000558e0feca600 R11: 0000000000000246 R12: 00007f6d6bb203c0
[    1.159583] R13: 00007f6d6bb1f880 R14: 00007ffff793bebc R15: 0000000000000100
[    1.159583]  ? native_iret+0x7/0x7
[    1.159583]  </#DF>
[    1.159583]  <SYSENTER>
[    1.159583] RIP: 0010:do_page_fault+0x0/0x100
[    1.159583] RSP: 0000:ffffffffff084070 EFLAGS: 00010097
[    1.159583]  page_fault+0x2c/0x60
[    1.159583] RIP: 0010:do_page_fault+0x0/0x100
[    1.159583] RSP: 0000:ffffffffff084120 EFLAGS: 00010012
[    1.159583] RAX: 00000000819d0a87 RBX: 0000000000000001 RCX: ffffffff819d0a87
[    1.159583] RDX: 0000000000001000 RSI: 0000000000000010 RDI: ffffffffff084128
[    1.159583] RBP: 0000000000000d68 R08: 00007f6d6bb24278 R09: 0000000000000023
[    1.159583] R10: 0000558e0feca600 R11: 0000000000000246 R12: 00007f6d6bb203c0
[    1.159583] R13: 00007f6d6bb1f880 R14: 00007ffff793bebc R15: 0000000000000100
[    1.159583]  ? native_iret+0x7/0x7
[    1.159583]  page_fault+0x2c/0x60
[    1.159583] RIP: 0010:apic_timer_interrupt+0x0/0xb0
[    1.159583] RSP: 0000:ffffffffff0841d8 EFLAGS: 00010046
[    1.159583] RAX: 0000000000000374 RBX: 0000558e0feca2c0 RCX: 00007f6d6b85aaf0
[    1.159583] RDX: 0000000000001000 RSI: 0000558e0feca600 RDI: 0000000000000000
[    1.159583] RBP: 0000000000000d68 R08: 00007f6d6bb24278 R09: 0000000000000023
[    1.159583] R10: 0000558e0feca600 R11: 0000000000000246 R12: 00007f6d6bb203c0
[    1.159583] R13: 00007f6d6bb1f880 R14: 00007ffff793bebc R15: 0000000000000100
[    1.159583] RIP: 0033:0x7f6d6b85aaf0
[    1.159583] RSP: 002b:00007ffff793bd68 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
[    1.159583] RAX: ffffffff819d2000 RBX: 00007f6d6b85aaf0 RCX: 0000000000000010
[    1.159583] RDX: 0000000000010046 RSI: ffffffffff0841d8 RDI: 0000000000000000
[    1.159583] RBP: 0000000000000374 R08: ffffffffffffffff R09: 0000000000000000
[    1.159583] R10: 0000558e0feca600 R11: 0000000000001000 R12: 00007f6d6bb24278
[    1.159583] R13: 0000000000000023 R14: 0000558e0feca600 R15: 0000000000000246
[    1.159583]  </SYSENTER>
[    1.159583] Kernel Offset: disabled
[    1.159583] ---[ end Kernel panic - not syncing: Machine halted.

 
-- 
Josh

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