[PATCH AUTOSEL 5.4 9/9] tpm: End any active auth session before shutdown

[PATCH AUTOSEL 5.4 9/9] tpm: End any active auth session before shutdown

[Sasha Levin]

From: Jonathan McDowell <noodles@meta.com>

[ Upstream commit 1dbf74e00a5f882b04b398399b6def65cd51ef21 ]

Lazy flushing of TPM auth sessions can interact badly with IMA + kexec,
resulting in loaded session handles being leaked across the kexec and
not cleaned up. Fix by ensuring any active auth session is ended before
the TPM is told about the shutdown, matching what is done when
suspending.

Before:

root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
root@debian-qemu-efi:~# kexec --load --kexec-file-syscall …
root@debian-qemu-efi:~# systemctl kexec
…
root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
- 0x2000000
root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
root@debian-qemu-efi:~#
(repeat kexec steps)
root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
- 0x2000000
- 0x2000001
root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
root@debian-qemu-efi:~#

After:

root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
root@debian-qemu-efi:~# kexec --load --kexec-file-syscall …
root@debian-qemu-efi:~# systemctl kexec
…
root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
root@debian-qemu-efi:~#

Signed-off-by: Jonathan McDowell <noodles@meta.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/char/tpm/tpm-chip.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index 17fbd7f7a2954..b33e938d80e8a 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -290,6 +290,7 @@ static int tpm_class_shutdown(struct device *dev)
 	down_write(&chip->ops_sem);
 	if (chip->flags & TPM_CHIP_FLAG_TPM2) {
 		if (!tpm_chip_start(chip)) {
+			tpm2_end_auth_session(chip);
 			tpm2_shutdown(chip, TPM2_SU_CLEAR);
 			tpm_chip_stop(chip);
 		}
-- 
2.39.5

Re: [PATCH AUTOSEL 5.4 9/9] tpm: End any active auth session before shutdown

[Jonathan McDowell]

NAK. Not sure on the logic that decided this was applicable for 5.4, but 
it's obviously not even been compile tested:

noodles@sevai:~/checkouts/linux$ git checkout v5.4.291
Updating files: 100% (13517/13517), done.
Previous HEAD position was 219d54332a09 Linux 5.4
HEAD is now at 52bcf31d8e3d Linux 5.4.291
noodles@sevai:~/checkouts/linux$ git grep tpm2_end_auth_session
noodles@sevai:~/checkouts/linux$ 

The auth session bits were introduced in 699e3efd6c645 (tpm: Add HMAC 
session start and end functions), which landed in 6.10.

On Thu, Apr 03, 2025 at 03:20:50PM -0400, Sasha Levin wrote:
>From: Jonathan McDowell <noodles@meta.com>
>
>[ Upstream commit 1dbf74e00a5f882b04b398399b6def65cd51ef21 ]
>
>Lazy flushing of TPM auth sessions can interact badly with IMA + kexec,
>resulting in loaded session handles being leaked across the kexec and
>not cleaned up. Fix by ensuring any active auth session is ended before
>the TPM is told about the shutdown, matching what is done when
>suspending.
>
>Before:
>
>root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
>root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
>root@debian-qemu-efi:~# kexec --load --kexec-file-syscall …
>root@debian-qemu-efi:~# systemctl kexec
>…
>root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
>- 0x2000000
>root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
>root@debian-qemu-efi:~#
>(repeat kexec steps)
>root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
>- 0x2000000
>- 0x2000001
>root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
>root@debian-qemu-efi:~#
>
>After:
>
>root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
>root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
>root@debian-qemu-efi:~# kexec --load --kexec-file-syscall …
>root@debian-qemu-efi:~# systemctl kexec
>…
>root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
>root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
>root@debian-qemu-efi:~#
>
>Signed-off-by: Jonathan McDowell <noodles@meta.com>
>Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
>Signed-off-by: Sasha Levin <sashal@kernel.org>
>---
> drivers/char/tpm/tpm-chip.c | 1 +
> 1 file changed, 1 insertion(+)
>
>diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
>index 17fbd7f7a2954..b33e938d80e8a 100644
>--- a/drivers/char/tpm/tpm-chip.c
>+++ b/drivers/char/tpm/tpm-chip.c
>@@ -290,6 +290,7 @@ static int tpm_class_shutdown(struct device *dev)
> 	down_write(&chip->ops_sem);
> 	if (chip->flags & TPM_CHIP_FLAG_TPM2) {
> 		if (!tpm_chip_start(chip)) {
>+			tpm2_end_auth_session(chip);
> 			tpm2_shutdown(chip, TPM2_SU_CLEAR);
> 			tpm_chip_stop(chip);
> 		}
>-- 
>2.39.5
>
>

J.

-- 
... Inside every living person there's a dead person trying to get out.

Re: [PATCH AUTOSEL 5.4 9/9] tpm: End any active auth session before shutdown

[Sasha Levin]

On Fri, Apr 04, 2025 at 08:28:03AM +0100, Jonathan McDowell wrote:
>NAK. Not sure on the logic that decided this was applicable for 5.4, 
>but it's obviously not even been compile tested:
>
>noodles@sevai:~/checkouts/linux$ git checkout v5.4.291
>Updating files: 100% (13517/13517), done.
>Previous HEAD position was 219d54332a09 Linux 5.4
>HEAD is now at 52bcf31d8e3d Linux 5.4.291
>noodles@sevai:~/checkouts/linux$ git grep tpm2_end_auth_session
>noodles@sevai:~/checkouts/linux$
>
>The auth session bits were introduced in 699e3efd6c645 (tpm: Add HMAC 
>session start and end functions), which landed in 6.10.

I'll drop it, thanks!

-- 
Thanks,
Sasha