| From bippy-7c5fe7eed585 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-2024-50102: x86: fix user address masking non-canonical speculation issue |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| x86: fix user address masking non-canonical speculation issue |
| |
| It turns out that AMD has a "Meltdown Lite(tm)" issue with non-canonical |
| accesses in kernel space. And so using just the high bit to decide |
| whether an access is in user space or kernel space ends up with the good |
| old "leak speculative data" if you have the right gadget using the |
| result: |
| |
| CVE-2020-12965 “Transient Execution of Non-Canonical Accesses“ |
| |
| Now, the kernel surrounds the access with a STAC/CLAC pair, and those |
| instructions end up serializing execution on older Zen architectures, |
| which closes the speculation window. |
| |
| But that was true only up until Zen 5, which renames the AC bit [1]. |
| That improves performance of STAC/CLAC a lot, but also means that the |
| speculation window is now open. |
| |
| Note that this affects not just the new address masking, but also the |
| regular valid_user_address() check used by access_ok(), and the asm |
| version of the sign bit check in the get_user() helpers. |
| |
| It does not affect put_user() or clear_user() variants, since there's no |
| speculative result to be used in a gadget for those operations. |
| |
| The Linux kernel CVE team has assigned CVE-2024-50102 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 6.4 with commit b19b74bc99b1501a550f4448d04d59b946dc617a and fixed in 6.11.6 with commit 291313693677a345d4f50aae3c68e28b469f601e |
| Issue introduced in 6.4 with commit b19b74bc99b1501a550f4448d04d59b946dc617a and fixed in 6.12 with commit 86e6b1547b3d013bc392adf775b89318441403c2 |
| |
| 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-2024-50102 |
| 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/include/asm/uaccess_64.h |
| arch/x86/kernel/cpu/common.c |
| arch/x86/kernel/vmlinux.lds.S |
| arch/x86/lib/getuser.S |
| |
| |
| 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/291313693677a345d4f50aae3c68e28b469f601e |
| https://git.kernel.org/stable/c/86e6b1547b3d013bc392adf775b89318441403c2 |
