CVE-2024-26706 parisc: Fix random data corruption from exception handler
A flaw in the Linux kernel's parisc exception handler can cause random data corruption, potentially leading to system instability or crashes.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2024-26706?
CVE-2024-26706 is a high-severity memory corruption vulnerability in Linux kernel, published on 3 Apr 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
parisc: Fix random data corruption from exception handler
The current exception handler implementation, which assists when accessing user space memory, may exhibit random data corruption if the compiler decides to use a different register than the specified register %r29 (defined in ASM_EXCEPTIONTABLE_REG) for the error code. If the compiler choose another register, the fault handler will nevertheless store -EFAULT into %r29 and thus trash whatever this register is used for. Looking at the assembly I found that this happens sometimes in emulate_ldd().
To solve the issue, the easiest solution would be if it somehow is possible to tell the fault handler which register is used to hold the error code. Using %0 or %1 in the inline assembly is not posssible as it will show up as e.g. %r29 (with the "%r" prefix), which the GNU assembler can not convert to an integer.
This patch takes another, better and more flexible approach: We extend the __ex_table (which is out of the execution path) by one 32-word. In this word we tell the compiler to insert the assembler instruction "or %r0,%r0,%reg", where %reg references the register which the compiler choosed for the error return code. In case of an access failure, the fault handler finds the __ex_table entry and can examine the opcode. The used register is encoded in the lowest 5 bits, and the fault handler can then store -EFAULT into this register.
Since we extend the __ex_table to 3 words we can't use the BUILDTIME_TABLE_SORT config option any longer.
Weakness: CWE-787
Which versions are affected by CVE-2024-26706?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-26706?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2024-26706 being exploited?
There is no known exploitation of CVE-2024-26706 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-58711, BELL-CVE-2024-26706, DEBIAN-CVE-2024-26706, GHSA-4fj7-85cf-9m8p, ROOT-OS-DEBIAN-11-CVE-2024-26706, UBUNTU-CVE-2024-26706.