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.
History

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cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published: 2024-04-03T14:55:09.529Z

Updated: 2024-11-05T09:14:14.288Z

Reserved: 2024-02-19T14:20:24.158Z

Link: CVE-2024-26706

cve-icon Vulnrichment

Updated: 2024-08-02T00:14:12.642Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2024-04-03T15:15:53.293

Modified: 2024-04-03T17:24:18.150

Link: CVE-2024-26706

cve-icon Redhat

Severity : Low

Publid Date: 2024-04-03T00:00:00Z

Links: CVE-2024-26706 - Bugzilla