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PUBLISHED

CVE-2024-26706

parisc: Fix random data corruption from exception handler

Reserved:2024-02-19
Published:2024-04-03
Updated:2024-04-03

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.

Product status

Default status
unaffected

1da177e4c3f4 before 23027309b099
affected

1da177e4c3f4 before fa69a8063f8b
affected

1da177e4c3f4 before ce31d79aa1f1
affected

1da177e4c3f4 before 8b1d72395635
affected

Default status
affected

6.1.79
unaffected

6.6.18
unaffected

6.7.6
unaffected

6.8
unaffected

References

https://git.kernel.org/stable/c/23027309b099ffc4efca5477009a11dccbdae592

https://git.kernel.org/stable/c/fa69a8063f8b27f3c7434a0d4f464a76a62f24d2

https://git.kernel.org/stable/c/ce31d79aa1f13a2345791f84935281a2c194e003

https://git.kernel.org/stable/c/8b1d72395635af45410b66cc4c4ab37a12c4a831

cve.org CVE-2024-26706

nvd.nist.gov CVE-2024-26706

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