github
/
arm-trusted-firmware
mirror of https://github.com/ARM-software/arm-trusted-firmware.git
1
0
Fork 0
Code Issues Projects Releases Wiki Activity
Browse Source

docs(threat-model): cover threats inherent to receiving data over UART 

TF-A supports reading input data from UART interfaces. This opens up
an attack vector for arbitrary data to be injected into TF-A, which is
not covered in the threat model right now.

Fill this gap by:

 - Updating the data flow diagrams. Data may flow from the UART into
   TF-A (and not only the other way around).

 - Documenting the threats inherent to reading untrusted data from a
   UART.

Change-Id: I508da5d2f7ad5d20717b958d76ab9337c5eca50f
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
pull/1993/merge
Sandrine Bailleux 1 year ago
parent
e7781c84e9
commit
348446ad2a
4 changed files with 62 additions and 7 deletions
Whitespace
Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL
Split View
Diff Options
Show Stats Download Patch File Download Diff File
  1. 4
      docs/resources/diagrams/plantuml/tfa_dfd.puml
  2. 4
      docs/resources/diagrams/plantuml/tfa_rss_dfd.puml
  3. 57
      docs/threat_model/threat_model.rst
  4. 4
      docs/threat_model/threat_model_fvp_r.rst

4
docs/resources/diagrams/plantuml/tfa_dfd.puml
View File

@ -25,7 +25,7 @@ digraph tfa_dfd {
nsec [label="Non-secure\nClients"]
sec [label="Secure\nClients"]
dbg [label="Debug & Trace"]
logs [label="Logs\n(UART)"]
uart [label="UART"]
nvm [label="Non-volatile\nMemory"]
# Trust boundary cluster
@ -56,7 +56,7 @@ digraph tfa_dfd {
# Interactions between nodes
nvm -> bl31 [lhead=cluster_tfa label="DF1"]
logs -> bl31 [dir="back" lhead=cluster_tfa label="DF2"]
uart -> bl31 [dir="both" lhead=cluster_tfa label="DF2"]
dbg -> bl2 [dir="both" lhead=cluster_tfa label="DF3"]
sec -> bl2 [dir="both" lhead=cluster_tfa label="DF4"]
nsec -> bl1 [dir="both" lhead=cluster_tfa, label="DF5"]

4
docs/resources/diagrams/plantuml/tfa_rss_dfd.puml
View File

@ -25,7 +25,7 @@ digraph tfa_dfd {
nsec [label="Non-secure\nClients"]
sec [label="Secure\nClients"]
dbg [label="Debug & Trace"]
logs [label="Logs\n(UART)"]
uart [label="UART"]
nvm [label="Non-volatile\nMemory"]
@ -65,7 +65,7 @@ digraph tfa_dfd {
# Interactions between nodes
nvm -> bl31 [lhead=cluster_tfa label="DF1"]
logs -> bl31 [dir="back" lhead=cluster_tfa label="DF2"]
uart -> bl31 [dir="both" lhead=cluster_tfa label="DF2"]
dbg -> bl2 [dir="both" lhead=cluster_tfa label="DF3"]
sec -> bl2 [dir="both" lhead=cluster_tfa label="DF4"]
nsec -> bl1 [dir="both" lhead=cluster_tfa, label="DF5"]

57
docs/threat_model/threat_model.rst
View File

@ -63,8 +63,10 @@ are considered untrusted by TF-A.
| | images include TF-A BL2 and BL31 images, as well as |
| | other secure and non-secure images. |
+-----------------+--------------------------------------------------------+
| DF2 | | TF-A log system framework outputs debug messages |
| | over a UART interface. |
| DF2 | | TF-A log system framework outputs debug or |
| | informative messages over a UART interface. |
| | |
| | | Also, characters can be read from a UART interface. |
+-----------------+--------------------------------------------------------+
| DF3 | | Debug and trace IP on a platform can allow access |
| | to registers and memory of TF-A. |
@ -552,6 +554,57 @@ General Threats for All Firmware Images
| | soon as they are not needed anymore. |
+------------------------+-----------------------------------------------------+
| Mitigations | | Yes / Platform specific |
| implemented? | |
+------------------------+-----------------------------------------------------+
+------------------------+-----------------------------------------------------+
| ID | 15 |
+========================+=====================================================+
| Threat | | **Improper handling of input data received over |
| | a UART interface may allow an attacker to tamper |
| | with TF-A execution environment.** |
| | |
| | | The consequences of the attack depend on the |
| | the exact usage of input data received over UART. |
| | Examples are injection of arbitrary data, |
| | sensitive data tampering, influencing the |
| | execution path, denial of service (if using |
| | blocking I/O). This list may not be exhaustive. |
+------------------------+-----------------------------------------------------+
| Diagram Elements | DF2, DF4, DF5 |
+------------------------+-----------------------------------------------------+
| Affected TF-A | BL1, BL2, BL31 |
| Components | |
+------------------------+-----------------------------------------------------+
| Assets | Sensitive Data, Code Execution, Availability |
+------------------------+-----------------------------------------------------+
| Threat Agent | NSCode, SecCode |
+------------------------+-----------------------------------------------------+
| Threat Type | Tampering, Information Disclosure, Denial of |
| | service, Elevation of privilege. |
+------------------------+-------------------+----------------+----------------+
| Application | Server | IoT | Mobile |
+------------------------+-------------------+----------------+----------------+
| Impact | Critical (5) | Critical (5) | Critical (5) |
+------------------------+-------------------+----------------+----------------+
| Likelihood | Critical (5) | Critical (5) | Critical (5) |
+------------------------+-------------------+----------------+----------------+
| Total Risk Rating | Critical (25) | Critical (25) | Critical (25) |
+------------------------+-------------------+----------------+----------------+
| Mitigations | | By default, the code to read input data from UART |
| | interfaces is disabled (see `ENABLE_CONSOLE_GETC` |
| | build option). It should only be enabled on a |
| | need basis. |
| | |
| | | Data received over UART interfaces should be |
| | treated as untrusted data. As such, it should be |
| | properly sanitized and handled with caution. |
+------------------------+-----------------------------------------------------+
| Mitigations | | Platform specific. |
| implemented? | |
| | | Generic code does not read any input data from |
| | UART interface(s). |
+------------------------+-----------------------------------------------------+

4
docs/threat_model/threat_model_fvp_r.rst
View File

@ -90,8 +90,10 @@ implementation:
and since the MPU configuration is equivalent with that for the fvp
platform and others, this is not expected to be a concern.
- ID 15: Improper handling of input data received over a UART interface may
allow an attacker to tamper with TF-A execution environment.
--------------
*Copyright (c) 2021, Arm Limited. All rights reserved.*
*Copyright (c) 2021-2023, Arm Limited. All rights reserved.*

Write Preview
Loading…
Cancel
Save