Bug 2028584 (CVE-2021-4093)
| Summary: | CVE-2021-4093 kernel: KVM: SVM: out-of-bounds read/write in sev_es_string_io | ||
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| Product: | [Other] Security Response | Reporter: | Guilherme de Almeida Suckevicz <gsuckevi> |
| Component: | vulnerability | Assignee: | Nobody <nobody> |
| Status: | NEW --- | QA Contact: | |
| Severity: | medium | Docs Contact: | |
| Priority: | medium | ||
| Version: | unspecified | CC: | acaringi, adscvr, airlied, alciregi, bhu, blc, chwhite, crwood, dvlasenk, hdegoede, hkrzesin, jarod, jarodwilson, jburrell, jeremy, jforbes, jglisse, jlelli, jonathan, josef, jshortt, jstancek, jwboyer, kcarcia, kernel-maint, kernel-mgr, lgoncalv, linville, masami256, mcascell, mchehab, mlangsdo, nmurray, ptalbert, qzhao, rvrbovsk, steved, vkumar, walters, williams |
| Target Milestone: | --- | Keywords: | Security |
| Target Release: | --- | ||
| Hardware: | All | ||
| OS: | Linux | ||
| Whiteboard: | |||
| Fixed In Version: | kernel 5.15 | Doc Type: | If docs needed, set a value |
| Doc Text: |
A flaw was found in the KVM's AMD code for supporting the Secure Encrypted Virtualization-Encrypted State (SEV-ES). A KVM guest using SEV-ES can trigger out-of-bounds reads and writes in the host kernel via a malicious VMGEXIT for a string I/O instruction (for example, outs or ins) using the exit reason SVM_EXIT_IOIO. This issue results in a crash of the entire system or a potential guest-to-host escape scenario.
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Story Points: | --- |
| Clone Of: | Environment: | ||
| Last Closed: | Type: | --- | |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
| Embargoed: | |||
| Bug Depends On: | 2006441, 2009338, 2009340, 2028585, 2031089, 2031090, 2031091 | ||
| Bug Blocks: | 2027465, 2031109 | ||
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Description
Guilherme de Almeida Suckevicz
2021-12-02 17:07:35 UTC
Created kernel tracking bugs for this issue: Affects: fedora-all [bug 2028585] This issue was fixed in upstream kernel v5.15. The main commit fix is: - KVM: SEV-ES: go over the sev_pio_data buffer in multiple passes if needed [https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=95e16b4] Together with the following preparative commits: - KVM: SEV-ES: rename guest_ins_data to sev_pio_data [https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b599840] - KVM: x86: leave vcpu->arch.pio.count alone in emulator_pio_in_out [https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0d33b1b] - KVM: SEV-ES: clean up kvm_sev_es_ins/outs [https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ea724ea] - KVM: x86: split the two parts of emulator_pio_in [https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3b27de2] - KVM: x86: remove unnecessary arguments from complete_emulator_pio_in [https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6b5efc9] - KVM: SEV-ES: keep INS functions together [https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4fa4b38] Also consider the following commit, which fixes a related issue: - KVM: SEV-ES: fix another issue with string I/O VMGEXITs [https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9b0971c] AMD SEV-ES support was introduced in upstream kernel v5.10: http://lkml.iu.edu/hypermail/linux/kernel/2010.1/05072.html RHEL-6 and RHEL-7 kernels are not affected by this flaw as they did not include support for SEV-ES (not even for SEV, FWIW). In reply to comment #0: > A KVM guest using SEV-ES (Secure Encrypted Virtualization - Encrypted State) > can trigger out-of-bounds reads and writes in the host kernel via a > malicious VMGEXIT using the exit reason SVM_EXIT_IOIO. In particular, the flaw occurs in sev_es_string_io() while handling string I/O instructions (e.g. outs or ins). The string is copied from the unencrypted guest memory into GHCB (Guest-Hypervisor Communication Block) using guest-controlled values for the length and I/O access size. At some point, the control flow will reach emulator_pio_out() where data is copied into `vcpu->arch.pio_data` which is only one virtual page size in length. If the guest provides a size that makes the memcpy() exceeds one page, it will trigger an out of bounds read/write access on adjacent pages. This was fixed for Fedora with the 5.14.15 stable kernel updates. |