CVE-2023-53642
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-10-07

Last updated on: 2026-02-03

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: x86: fix clear_user_rep_good() exception handling annotation This code no longer exists in mainline, because it was removed in commit d2c95f9d6802 ("x86: don't use REP_GOOD or ERMS for user memory clearing") upstream. However, rather than backport the full range of x86 memory clearing and copying cleanups, fix the exception table annotation placement for the final 'rep movsb' in clear_user_rep_good(): rather than pointing at the actual instruction that did the user space access, it pointed to the register move just before it. That made sense from a code flow standpoint, but not from an actual usage standpoint: it means that if user access takes an exception, the exception handler won't actually find the instruction in the exception tables. As a result, rather than fixing it up and returning -EFAULT, it would then turn it into a kernel oops report instead, something like: BUG: unable to handle page fault for address: 0000000020081000 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page ... RIP: 0010:clear_user_rep_good+0x1c/0x30 arch/x86/lib/clear_page_64.S:147 ... Call Trace: __clear_user arch/x86/include/asm/uaccess_64.h:103 [inline] clear_user arch/x86/include/asm/uaccess_64.h:124 [inline] iov_iter_zero+0x709/0x1290 lib/iov_iter.c:800 iomap_dio_hole_iter fs/iomap/direct-io.c:389 [inline] iomap_dio_iter fs/iomap/direct-io.c:440 [inline] __iomap_dio_rw+0xe3d/0x1cd0 fs/iomap/direct-io.c:601 iomap_dio_rw+0x40/0xa0 fs/iomap/direct-io.c:689 ext4_dio_read_iter fs/ext4/file.c:94 [inline] ext4_file_read_iter+0x4be/0x690 fs/ext4/file.c:145 call_read_iter include/linux/fs.h:2183 [inline] do_iter_readv_writev+0x2e0/0x3b0 fs/read_write.c:733 do_iter_read+0x2f2/0x750 fs/read_write.c:796 vfs_readv+0xe5/0x150 fs/read_write.c:916 do_preadv+0x1b6/0x270 fs/read_write.c:1008 __do_sys_preadv2 fs/read_write.c:1070 [inline] __se_sys_preadv2 fs/read_write.c:1061 [inline] __x64_sys_preadv2+0xef/0x150 fs/read_write.c:1061 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd which then looks like a filesystem bug rather than the incorrect exception annotation that it is. [ The alternative to this one-liner fix is to take the upstream series that cleans this all up: 68674f94ffc9 ("x86: don't use REP_GOOD or ERMS for small memory copies") 20f3337d350c ("x86: don't use REP_GOOD or ERMS for small memory clearing") adfcf4231b8c ("x86: don't use REP_GOOD or ERMS for user memory copies") * d2c95f9d6802 ("x86: don't use REP_GOOD or ERMS for user memory clearing") 3639a535587d ("x86: move stac/clac from user copy routines into callers") 577e6a7fd50d ("x86: inline the 'rep movs' in user copies for the FSRM case") 8c9b6a88b7e2 ("x86: improve on the non-rep 'clear_user' function") 427fda2c8a49 ("x86: improve on the non-rep 'copy_user' function") * e046fe5a36a9 ("x86: set FSRS automatically on AMD CPUs that have FSRM") e1f2750edc4a ("x86: remove 'zerorest' argument from __copy_user_nocache()") 034ff37d3407 ("x86: rewrite '__copy_user_nocache' function") with either the whole series or at a minimum the two marked commits being needed to fix this issue ]
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Meta Information
Published
2025-10-07
Last Modified
2026-02-03
Generated
2026-05-07
AI Q&A
2025-10-07
EPSS Evaluated
2026-05-05
NVD
CVE-2023-53642
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel From 5.15.160 (inc) to 5.16 (inc)
Helpful Resources
Exploitability
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CWE ID Description
CWE-UNKNOWN
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability is in the Linux kernel's x86 architecture code, specifically in the exception handling annotation for the clear_user_rep_good() function. The annotation pointed to the wrong instruction, so when a user memory access caused an exception, the kernel's exception handler could not properly identify the faulting instruction. Instead of returning an error (-EFAULT), the kernel would generate a kernel oops (a crash report), which looks like a filesystem bug rather than an exception annotation issue. The vulnerability was fixed by correcting the exception table annotation to point to the actual instruction causing the user space access.


How can this vulnerability impact me? :

If this vulnerability is triggered, it can cause the Linux kernel to crash or produce a kernel oops report instead of properly handling a user memory access exception. This can lead to system instability or unexpected crashes, potentially affecting system reliability and availability.


What immediate steps should I take to mitigate this vulnerability?

The vulnerability is fixed by correcting the exception table annotation placement in the Linux kernel code for the clear_user_rep_good() function. To mitigate this vulnerability, you should update your Linux kernel to a version that includes this fix or later. The fix involves applying the patch that corrects the exception handling annotation or upgrading to a kernel version that has removed the problematic code and implemented the fix described.


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