In the Linux kernel, the following vulnerability has been resolved:
riscv: fix runtime constant support for nommu kernels
the `__runtime_fixup_32` function does not handle the case where `val` is
zero correctly (as might occur when patching a nommu kernel and referring
to a physical address below the 4GiB boundary whose upper 32 bits are all
zero) because nothing in the existing logic prevents the code from taking
the `else` branch of both nop-checks and emitting two `nop` instructions.
This leaves random garbage in the register that is supposed to receive the
upper 32 bits of the pointer instead of zero that when combined with the
value for the lower 32 bits yields an invalid pointer and causes a kernel
panic when that pointer is eventually accessed.
The author clearly considered the fact that if the `lui` is converted into
a `nop` that the second instruction needs to be adjusted to become an `li`
instead of an `addi`, hence introducing the `addi_insn_mask` variable, but
didn't follow that logic through fully to the case where the `else` branch
executes. To fix it just adjust the logic to ensure that the second `else`
branch is not taken if the first instruction will be patched to a `nop`.
Metrics
Affected Vendors & Products
| Vendors | Products |
|---|---|
| Linux |
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No data.
No data.
References
History
Tue, 29 Jul 2025 12:30:00 +0000
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| Metrics |
threat_severity
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cvssV3_1
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Sat, 26 Jul 2025 12:15:00 +0000
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| First Time appeared |
Linux
Linux linux Kernel |
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| Vendors & Products |
Linux
Linux linux Kernel |
Fri, 25 Jul 2025 14:45:00 +0000
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| Description | In the Linux kernel, the following vulnerability has been resolved: riscv: fix runtime constant support for nommu kernels the `__runtime_fixup_32` function does not handle the case where `val` is zero correctly (as might occur when patching a nommu kernel and referring to a physical address below the 4GiB boundary whose upper 32 bits are all zero) because nothing in the existing logic prevents the code from taking the `else` branch of both nop-checks and emitting two `nop` instructions. This leaves random garbage in the register that is supposed to receive the upper 32 bits of the pointer instead of zero that when combined with the value for the lower 32 bits yields an invalid pointer and causes a kernel panic when that pointer is eventually accessed. The author clearly considered the fact that if the `lui` is converted into a `nop` that the second instruction needs to be adjusted to become an `li` instead of an `addi`, hence introducing the `addi_insn_mask` variable, but didn't follow that logic through fully to the case where the `else` branch executes. To fix it just adjust the logic to ensure that the second `else` branch is not taken if the first instruction will be patched to a `nop`. | |
| Title | riscv: fix runtime constant support for nommu kernels | |
| References |
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published: 2025-07-25T14:32:07.122Z
Updated: 2025-07-28T04:22:06.009Z
Reserved: 2025-04-16T04:51:24.015Z
Link: CVE-2025-38433
Vulnrichment
No data.
NVD
Status : Awaiting Analysis
Published: 2025-07-25T15:15:28.570
Modified: 2025-07-25T15:29:19.837
Link: CVE-2025-38433
Redhat