CVE-2021-47350 Affecting kernel-preempt package, versions <5.3.18-150300.59.164.1
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-SLES153-KERNELPREEMPT-7365546
- published25 Jun 2024
- disclosed24 Jun 2024
Introduced: 24 Jun 2024
CVE-2021-47350 (opens in a new tab)How to fix?
Upgrade SLES:15.3 kernel-preempt to version 5.3.18-150300.59.164.1 or higher.
NVD Description
Note: Versions mentioned in the description apply only to the upstream kernel-preempt package and not the kernel-preempt package as distributed by SLES.
See How to fix? for SLES:15.3 relevant fixed versions and status.
In the Linux kernel, the following vulnerability has been resolved:
powerpc/mm: Fix lockup on kernel exec fault
The powerpc kernel is not prepared to handle exec faults from kernel. Especially, the function is_exec_fault() will return 'false' when an exec fault is taken by kernel, because the check is based on reading current->thread.regs->trap which contains the trap from user.
For instance, when provoking a LKDTM EXEC_USERSPACE test, current->thread.regs->trap is set to SYSCALL trap (0xc00), and the fault taken by the kernel is not seen as an exec fault by set_access_flags_filter().
Commit d7df2443cd5f ("powerpc/mm: Fix spurious segfaults on radix with autonuma") made it clear and handled it properly. But later on commit d3ca587404b3 ("powerpc/mm: Fix reporting of kernel execute faults") removed that handling, introducing test based on error_code. And here is the problem, because on the 603 all upper bits of SRR1 get cleared when the TLB instruction miss handler bails out to ISI.
Until commit cbd7e6ca0210 ("powerpc/fault: Avoid heavy search_exception_tables() verification"), an exec fault from kernel at a userspace address was indirectly caught by the lack of entry for that address in the exception tables. But after that commit the kernel mainly relies on KUAP or on core mm handling to catch wrong user accesses. Here the access is not wrong, so mm handles it. It is a minor fault because PAGE_EXEC is not set, set_access_flags_filter() should set PAGE_EXEC and voila. But as is_exec_fault() returns false as explained in the beginning, set_access_flags_filter() bails out without setting PAGE_EXEC flag, which leads to a forever minor exec fault.
As the kernel is not prepared to handle such exec faults, the thing to do is to fire in bad_kernel_fault() for any exec fault taken by the kernel, as it was prior to commit d3ca587404b3.
References
- https://www.suse.com/security/cve/CVE-2021-47350.html
- https://bugzilla.suse.com/1225181
- https://git.kernel.org/stable/c/500f81cec9f1bfa5210aa9dd5ba9a06e22f62a35
- https://git.kernel.org/stable/c/8a96ec5ebf96ad8e2ba7b1b34103a0be5140fc70
- https://git.kernel.org/stable/c/a82471a14aad90f79d1608d2bcbb019f0ffb53f0
- https://git.kernel.org/stable/c/cd5d5e602f502895e47e18cd46804d6d7014e65c
- https://git.kernel.org/stable/c/d2e52d4664097a6c1f591d869ec594bd7a0d4925