On 12/20/21 19:39, Tyrel Datwyler wrote:
On 12/11/21 5:28 PM, Stefan Berger wrote:
Fix the following crash on kexec by checking chip->ops for a NULL pointer
in tpm_chip_start() and returning an error code if this is the case.
BUG: Kernel NULL pointer dereference on read at 0x00000060
Faulting instruction address: 0xc00000000099a06c
Oops: Kernel access of bad area, sig: 11 [#1]
...
NIP [c00000000099a06c] tpm_chip_start+0x2c/0x140
LR [c00000000099a808] tpm_chip_unregister+0x108/0x170
Call Trace:
[c0000000188bfa00] [c000000002b03930] fw_devlink_strict+0x0/0x8 (unreliable)
[c0000000188bfa30] [c00000000099a808] tpm_chip_unregister+0x108/0x170
[c0000000188bfa70] [c0000000009a3874] tpm_ibmvtpm_remove+0x34/0x130
[c0000000188bfae0] [c000000000110dbc] vio_bus_remove+0x5c/0xb0
[c0000000188bfb20] [c0000000009bc154] device_shutdown+0x1d4/0x3a8
[c0000000188bfbc0] [c000000000196e14] kernel_restart_prepare+0x54/0x70
The referenced patch below introduced a function to shut down the VIO bus.
The bus shutdown now calls tpm_del_char_device (via tpm_chip_unregister)
after a call to tpm_class_shutdown, which already set chip->ops to NULL.
The crash occurrs when tpm_del_char_device calls tpm_chip_start with the
chip->ops NULL pointer.
It was unclear to me at first, but IIUC the problem is the ibmvtpm device
receives two shutdown calls, the first is a class shutdown call for TPM devices,
followed by a bus shutdown call for VIO devices.
It appears that the class shutdown routines are meant to be a pre-shutdown
routine as they are defined as class->shutdown_pre(), and it is clearly allowed
to call class->shutdown_pre() followed by one of but not both of the following
bus->shutdown() or driver->shutdown(). Even tpm_class_shutdown() mentions in the
function comment that bus/device shutdown to follow.
I suppose you are referring to this here:
/**
* tpm_class_shutdown() - prepare the TPM device for loss of power.
* @dev: device to which the chip is associated.
*
* Issues a TPM2_Shutdown command prior to loss of power, as required
by the
* TPM 2.0 spec. Then, calls bus- and device- specific shutdown code.
*
* Return: always 0 (i.e. success)
*/
I think this comment still refers to the ancient code here:
https://elixir.bootlin.com/linux/v4.4.295/source/drivers/char/tpm/tpm-chip.c#L161
if (dev->bus && dev->bus->shutdown)
dev->bus->shutdown(dev);
else if (dev->driver && dev->driver->shutdown)
dev->driver->shutdown(dev);
Fixes: 39d0099f9439 ("powerpc/pseries: Add shutdown() to vio_driver and vio_bus")
This patch left implementing each vio driver shutdown routine as an exercise for
the respective maintainers, and instead just big hammers anything that doesn't
have a shutdown routine by calling the driver->remove().
If tpm_class_shutdown() quiecses ibmvtpm enough implementing a no-op
ibmvtpm->shutdown() with a comment saying so suffices.
However, the generic TPM code is still introducing a bug that an attempt to call
tpm_chip_unregister() after tpm_class_shutdown() will crash as mentioned above.
An alternative solution may be this here:
diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index ddaeceb7e109..4cb908349b31 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -473,15 +473,8 @@ static void tpm_del_char_device(struct tpm_chip *chip)
mutex_unlock(&idr_lock);
/* Make the driver uncallable. */
- down_write(&chip->ops_sem);
- if (chip->flags & TPM_CHIP_FLAG_TPM2) {
- if (!tpm_chip_start(chip)) {
- tpm2_shutdown(chip, TPM2_SU_CLEAR);
- tpm_chip_stop(chip);
- }
- }
- chip->ops = NULL;
- up_write(&chip->ops_sem);
+ if (chip->ops)
+ tpm_class_shutdown(&chip->dev);
}
static void tpm_del_legacy_sysfs(struct tpm_chip *chip)
I could post this as v2 ?! Let me know...
Stefan
Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
---
drivers/char/tpm/tpm-chip.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index ddaeceb7e109..cca1bde296ee 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -101,6 +101,9 @@ int tpm_chip_start(struct tpm_chip *chip)
{
int ret;
+ if (!chip->ops)
+ return -EINVAL;
+
I wonder if a better fix would to have tpm_del_char_device() check for valid
chip->ops and call tpm_class_shutdown() when the ops are still valid. Calling
tpm_class_shutdown() allows for some code deduplication in tpm_del_char_device().
-Tyrel
tpm_clk_enable(chip);
if (chip->locality == -1) {
