CVE-2024-26670: arm64: entry: fix ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD
Description
In the Linux kernel, the following vulnerability has been resolved:
arm64: entry: fix ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD
Currently the ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD workaround isn't
quite right, as it is supposed to be applied after the last explicit
memory access, but is immediately followed by an LDR.
The ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD workaround is used to
handle Cortex-A520 erratum 2966298 and Cortex-A510 erratum 3117295,
which are described in:
* https://developer.arm.com/documentation/SDEN2444153/0600/?lang=en
* https://developer.arm.com/documentation/SDEN1873361/1600/?lang=en
In both cases the workaround is described as:
| If pagetable isolation is disabled, the context switch logic in the
| kernel can be updated to execute the following sequence on affected
| cores before exiting to EL0, and after all explicit memory accesses:
|
| 1. A non-shareable TLBI to any context and/or address, including
| unused contexts or addresses, such as a `TLBI VALE1 Xzr`.
|
| 2. A DSB NSH to guarantee completion of the TLBI.
The important part being that the TLBI+DSB must be placed "after all
explicit memory accesses".
Unfortunately, as-implemented, the TLBI+DSB is immediately followed by
an LDR, as we have:
| alternative_if ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD
| tlbi vale1, xzr
| dsb nsh
| alternative_else_nop_endif
| alternative_if_not ARM64_UNMAP_KERNEL_AT_EL0
| ldr lr, [sp, #S_LR]
| add sp, sp, #PT_REGS_SIZE // restore sp
| eret
| ...
Classification
CVE ID: CVE-2024-26670
Affected Products
Vendor: Linux
Product: Linux
Exploit Prediction Scoring System (EPSS)
EPSS Score: 0.05% (probability of being exploited)
EPSS Percentile: 17.83% (scored less or equal to compared to others)
EPSS Date: 2025-02-04 (when was this score calculated)
References
https://git.kernel.org/stable/c/58eb5c07f41704464b9acc09ab0707b6769db6c0https://git.kernel.org/stable/c/baa0aaac16432019651e0d60c41cd34a0c3c3477
https://git.kernel.org/stable/c/832dd634bd1b4e3bbe9f10b9c9ba5db6f6f2b97f