On 12/21/21 09:01, Stefan Berger wrote:
On 12/21/21 03:47, Jarkko Sakkinen wrote:
On Sat, Dec 11, 2021 at 08:28:04PM -0500, 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.
Fixes: 39d0099f9439 ("powerpc/pseries: Add shutdown() to vio_driver
and vio_bus")
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;
This triggers to all drivers, not just tpm_ibmvtpm, i.e. the fix has
side-effects.
What are those side-effects?
I am asking because if one entered tpm_chip_start() with chip->ops =
NULL it would crash any system. So now the side-effect is that one can
call this function without crashing the system but gets an -EINVAL back.
Another alternative that prevents these crashes is this change here
including code deduplication:
diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index ddaeceb7e109..888d37293091 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -296,7 +296,7 @@ static int tpm_class_shutdown(struct device *dev)
struct tpm_chip *chip = container_of(dev, struct tpm_chip, dev);
down_write(&chip->ops_sem);
- if (chip->flags & TPM_CHIP_FLAG_TPM2) {
+ if (chip->ops && chip->flags & TPM_CHIP_FLAG_TPM2) {
if (!tpm_chip_start(chip)) {
tpm2_shutdown(chip, TPM2_SU_CLEAR);
tpm_chip_stop(chip);
@@ -473,15 +473,7 @@ 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);
+ tpm_class_shutdown(&chip->dev);
}
static void tpm_del_legacy_sysfs(struct tpm_chip *chip)
Stefan
