Re: [PATCH] ACPI / CPPC: Fix per-CPU pointers management

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Saturday, December 10, 2016 12:52:28 AM Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> Enabling ACPI CPPC on x86 causes a NULL pointer dereference to occur
> (on boot on a "default" KVM setup) in acpi_cppc_processor_exit() due
> to a missing check against NULL in there:
> 
> |BUG: unable to handle kernel NULL pointer dereference at           (null)
> |IP: [<ffffffff812aab6e>] acpi_cppc_processor_exit+0x40/0x60
> |PGD 0 [    0.577616]
> |Oops: 0000 [#1] SMP
> |Modules linked in:
> |CPU: 3 PID: 1 Comm: swapper/0 Not tainted 4.9.0-rc6-00146-g17669006adf6 #51
> |task: ffff88003f878000 task.stack: ffffc90000008000
> |RIP: 0010:[<ffffffff812aab6e>]  [<ffffffff812aab6e>] acpi_cppc_processor_exit+0x40/0x60
> |RSP: 0000:ffffc9000000bd48  EFLAGS: 00010296
> |RAX: 00000000000137e0 RBX: 0000000000000000 RCX: 0000000000000001
> |RDX: ffff88003fc00000 RSI: 0000000000000000 RDI: ffff88003fbca130
> |RBP: ffffc9000000bd60 R08: 0000000000000514 R09: 0000000000000000
> |R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000002
> |R13: 0000000000000020 R14: ffffffff8167cb00 R15: 0000000000000000
> |FS:  0000000000000000(0000) GS:ffff88003fcc0000(0000) knlGS:0000000000000000
> |CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> |CR2: 0000000000000000 CR3: 0000000001618000 CR4: 00000000000406e0
> |Stack:
> | ffff88003f939848 ffff88003fbca130 0000000000000001 ffffc9000000bd80
> | ffffffff812a4ccb ffff88003fc0cee8 0000000000000000 ffffc9000000bdb8
> | ffffffff812dc20d ffff88003fc0cee8 ffffffff8167cb00 ffff88003fc0cf48
> |Call Trace:
> | [<ffffffff812a4ccb>] acpi_processor_stop+0xb2/0xc5
> | [<ffffffff812dc20d>] driver_probe_device+0x14d/0x2f0
> | [<ffffffff812dc41e>] __driver_attach+0x6e/0x90
> | [<ffffffff812da234>] bus_for_each_dev+0x54/0x90
> | [<ffffffff812dbbf9>] driver_attach+0x19/0x20
> | [<ffffffff812db6a6>] bus_add_driver+0xe6/0x200
> | [<ffffffff812dcb23>] driver_register+0x83/0xc0
> | [<ffffffff816f050a>] acpi_processor_driver_init+0x20/0x94
> | [<ffffffff81000487>] do_one_initcall+0x97/0x180
> | [<ffffffff816ccf5c>] kernel_init_freeable+0x112/0x1a6
> | [<ffffffff813a0fc9>] kernel_init+0x9/0xf0
> | [<ffffffff813acf35>] ret_from_fork+0x25/0x30
> |Code: 02 00 00 00 48 8b 14 d5 e0 c3 55 81 48 8b 1c 02 4c 8d 6b 20 eb 15 49 8b 7d 00 48 85 ff 74 05 e8 39 8c d9 ff 41 ff c4 49 83 c5 20 <44> 3b 23 72 e6 48 8d bb a0 02 00 00 e8 b1 6f f9 ff 48 89 df e8
> |RIP  [<ffffffff812aab6e>] acpi_cppc_processor_exit+0x40/0x60
> | RSP <ffffc9000000bd48>
> |CR2: 0000000000000000
> 
> Fix that and while at it, fix a possible use-after-free scenario in
> acpi_cppc_processor_probe() that can happen if the function returns
> without cleaning up the per-CPU pointer set by it previously.
> 
> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Original-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> 
> Hi Thomas,
> 
> The crash fixed by this is exposed by the ITMT (asymmetric packing) series
> (which involves using ACPI CPPC on x86), so IMO it would be good to route it
> through tip along with that series.

The problematic commit has gone in already, so I'll route the fix through
the ACPI tree.

Thanks,
Rafael