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Date: Wed, 3 Apr 2024 16:55:57 +0200 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-cve-announce@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org> Subject: CVE-2024-26706: parisc: Fix random data corruption from exception handler 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. The Linux kernel CVE team has assigned CVE-2024-26706 to this issue. Affected and fixed versions =========================== Fixed in 6.1.79 with commit 23027309b099 Fixed in 6.6.18 with commit fa69a8063f8b Fixed in 6.7.6 with commit ce31d79aa1f1 Fixed in 6.8 with commit 8b1d72395635 Please see https://www.kernel.org for a full list of currently supported kernel versions by the kernel community. Unaffected versions might change over time as fixes are backported to older supported kernel versions. The official CVE entry at https://cve.org/CVERecord/?id=CVE-2024-26706 will be updated if fixes are backported, please check that for the most up to date information about this issue. Affected files ============== The file(s) affected by this issue are: arch/parisc/Kconfig arch/parisc/include/asm/assembly.h arch/parisc/include/asm/extable.h arch/parisc/include/asm/special_insns.h arch/parisc/include/asm/uaccess.h arch/parisc/kernel/cache.c arch/parisc/kernel/unaligned.c arch/parisc/mm/fault.c Mitigation ========== The Linux kernel CVE team recommends that you update to the latest stable kernel version for this, and many other bugfixes. Individual changes are never tested alone, but rather are part of a larger kernel release. Cherry-picking individual commits is not recommended or supported by the Linux kernel community at all. If however, updating to the latest release is impossible, the individual changes to resolve this issue can be found at these commits: 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
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