Trusted Firmware-A (TF-A) before 2.10 has a potential read out-of-bounds in the SDEI service. The input parameter passed in register x1 is not validated well enough in the function sdei_interrupt_bind. The parameter is passed to a call to plat_ic_get_interrupt_type. It can be any arbitrary value passing checks in the function plat_ic_is_sgi. A compromised Normal World (Linux kernel) can enable a root-privileged attacker to issue arbitrary SMC calls. Using this primitive, he can control the content of registers x0 through x6, which are used to send parameters to TF-A. Out-of-bounds addresses can be read in the context of TF-A (EL3). Because the read value is never returned to non-secure memory or in registers, no leak is possible. An attacker can still crash TF-A, however.
Weakness
The product reads data past the end, or before the beginning, of the intended buffer.
Affected Software
| Name |
Vendor |
Start Version |
End Version |
| Arm-trusted-firmware |
Ubuntu |
esm-apps/focal |
* |
| Arm-trusted-firmware |
Ubuntu |
esm-apps/jammy |
* |
| Arm-trusted-firmware |
Ubuntu |
focal |
* |
| Arm-trusted-firmware |
Ubuntu |
jammy |
* |
| Arm-trusted-firmware |
Ubuntu |
mantic |
* |
Potential Mitigations
- Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
- When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
- Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.
References