| 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-2024-35917: s390/bpf: Fix bpf_plt pointer arithmetic |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| s390/bpf: Fix bpf_plt pointer arithmetic |
| |
| Kui-Feng Lee reported a crash on s390x triggered by the |
| dummy_st_ops/dummy_init_ptr_arg test [1]: |
| |
| [<0000000000000002>] 0x2 |
| [<00000000009d5cde>] bpf_struct_ops_test_run+0x156/0x250 |
| [<000000000033145a>] __sys_bpf+0xa1a/0xd00 |
| [<00000000003319dc>] __s390x_sys_bpf+0x44/0x50 |
| [<0000000000c4382c>] __do_syscall+0x244/0x300 |
| [<0000000000c59a40>] system_call+0x70/0x98 |
| |
| This is caused by GCC moving memcpy() after assignments in |
| bpf_jit_plt(), resulting in NULL pointers being written instead of |
| the return and the target addresses. |
| |
| Looking at the GCC internals, the reordering is allowed because the |
| alias analysis thinks that the memcpy() destination and the assignments' |
| left-hand-sides are based on different objects: new_plt and |
| bpf_plt_ret/bpf_plt_target respectively, and therefore they cannot |
| alias. |
| |
| This is in turn due to a violation of the C standard: |
| |
| When two pointers are subtracted, both shall point to elements of the |
| same array object, or one past the last element of the array object |
| ... |
| |
| From the C's perspective, bpf_plt_ret and bpf_plt are distinct objects |
| and cannot be subtracted. In the practical terms, doing so confuses the |
| GCC's alias analysis. |
| |
| The code was written this way in order to let the C side know a few |
| offsets defined in the assembly. While nice, this is by no means |
| necessary. Fix the noncompliance by hardcoding these offsets. |
| |
| [1] https://lore.kernel.org/bpf/c9923c1d-971d-4022-8dc8-1364e929d34c@gmail.com/ |
| |
| The Linux kernel CVE team has assigned CVE-2024-35917 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 6.3 with commit f1d5df84cd8c3ec6460c78f5b86be7c84577a83f and fixed in 6.6.26 with commit c3062bdb859b6e2567e7f5c8cde20c0250bb130f |
| Issue introduced in 6.3 with commit f1d5df84cd8c3ec6460c78f5b86be7c84577a83f and fixed in 6.8.5 with commit d3d74e45a060d218fe4b0c9174f0a77517509d8e |
| Issue introduced in 6.3 with commit f1d5df84cd8c3ec6460c78f5b86be7c84577a83f and fixed in 6.9 with commit 7ded842b356d151ece8ac4985940438e6d3998bb |
| |
| 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-2024-35917 |
| 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/s390/net/bpf_jit_comp.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/c3062bdb859b6e2567e7f5c8cde20c0250bb130f |
| https://git.kernel.org/stable/c/d3d74e45a060d218fe4b0c9174f0a77517509d8e |
| https://git.kernel.org/stable/c/7ded842b356d151ece8ac4985940438e6d3998bb |
