| From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2024-56761: x86/fred: Clear WFE in missing-ENDBRANCH #CPs |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| x86/fred: Clear WFE in missing-ENDBRANCH #CPs |
| |
| An indirect branch instruction sets the CPU indirect branch tracker |
| (IBT) into WAIT_FOR_ENDBRANCH (WFE) state and WFE stays asserted |
| across the instruction boundary. When the decoder finds an |
| inappropriate instruction while WFE is set ENDBR, the CPU raises a #CP |
| fault. |
| |
| For the "kernel IBT no ENDBR" selftest where #CPs are deliberately |
| triggered, the WFE state of the interrupted context needs to be |
| cleared to let execution continue. Otherwise when the CPU resumes |
| from the instruction that just caused the previous #CP, another |
| missing-ENDBRANCH #CP is raised and the CPU enters a dead loop. |
| |
| This is not a problem with IDT because it doesn't preserve WFE and |
| IRET doesn't set WFE. But FRED provides space on the entry stack |
| (in an expanded CS area) to save and restore the WFE state, thus the |
| WFE state is no longer clobbered, so software must clear it. |
| |
| Clear WFE to avoid dead looping in ibt_clear_fred_wfe() and the |
| !ibt_fatal code path when execution is allowed to continue. |
| |
| Clobbering WFE in any other circumstance is a security-relevant bug. |
| |
| [ dhansen: changelog rewording ] |
| |
| The Linux kernel CVE team has assigned CVE-2024-56761 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 6.6 with commit a5f6c2ace9974adf92ce65dacca8126d90adabfe and fixed in 6.6.70 with commit 151447859d6fb0dcce8259f0971c6e94fb801661 |
| Issue introduced in 6.6 with commit a5f6c2ace9974adf92ce65dacca8126d90adabfe and fixed in 6.12.8 with commit b939f108e86b76119428a6fa4e92491e09ac7867 |
| Issue introduced in 6.6 with commit a5f6c2ace9974adf92ce65dacca8126d90adabfe and fixed in 6.13 with commit dc81e556f2a017d681251ace21bf06c126d5a192 |
| |
| 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-2024-56761 |
| 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/x86/kernel/cet.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/151447859d6fb0dcce8259f0971c6e94fb801661 |
| https://git.kernel.org/stable/c/b939f108e86b76119428a6fa4e92491e09ac7867 |
| https://git.kernel.org/stable/c/dc81e556f2a017d681251ace21bf06c126d5a192 |
