| 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-2021-47430: x86/entry: Clear X86_FEATURE_SMAP when CONFIG_X86_SMAP=n |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| x86/entry: Clear X86_FEATURE_SMAP when CONFIG_X86_SMAP=n |
| |
| Commit |
| |
| 3c73b81a9164 ("x86/entry, selftests: Further improve user entry sanity checks") |
| |
| added a warning if AC is set when in the kernel. |
| |
| Commit |
| |
| 662a0221893a3d ("x86/entry: Fix AC assertion") |
| |
| changed the warning to only fire if the CPU supports SMAP. |
| |
| However, the warning can still trigger on a machine that supports SMAP |
| but where it's disabled in the kernel config and when running the |
| syscall_nt selftest, for example: |
| |
| ------------[ cut here ]------------ |
| WARNING: CPU: 0 PID: 49 at irqentry_enter_from_user_mode |
| CPU: 0 PID: 49 Comm: init Tainted: G T 5.15.0-rc4+ #98 e6202628ee053b4f310759978284bd8bb0ce6905 |
| Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014 |
| RIP: 0010:irqentry_enter_from_user_mode |
| ... |
| Call Trace: |
| ? irqentry_enter |
| ? exc_general_protection |
| ? asm_exc_general_protection |
| ? asm_exc_general_protectio |
| |
| IS_ENABLED(CONFIG_X86_SMAP) could be added to the warning condition, but |
| even this would not be enough in case SMAP is disabled at boot time with |
| the "nosmap" parameter. |
| |
| To be consistent with "nosmap" behaviour, clear X86_FEATURE_SMAP when |
| !CONFIG_X86_SMAP. |
| |
| Found using entry-fuzz + satrandconfig. |
| |
| [ bp: Massage commit message. ] |
| |
| The Linux kernel CVE team has assigned CVE-2021-47430 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 5.8 with commit 3c73b81a9164d0c1b6379d6672d2772a9e95168e and fixed in 5.10.73 with commit f2447f6587b8ffe42ba04d14ce67d429a1163e5e |
| Issue introduced in 5.8 with commit 3c73b81a9164d0c1b6379d6672d2772a9e95168e and fixed in 5.14.12 with commit 4e9ec1c65da98c293f75d83755dfa5e03075a6d0 |
| Issue introduced in 5.8 with commit 3c73b81a9164d0c1b6379d6672d2772a9e95168e and fixed in 5.15 with commit 3958b9c34c2729597e182cc606cc43942fd19f7c |
| |
| 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-2021-47430 |
| 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/cpu/common.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/f2447f6587b8ffe42ba04d14ce67d429a1163e5e |
| https://git.kernel.org/stable/c/4e9ec1c65da98c293f75d83755dfa5e03075a6d0 |
| https://git.kernel.org/stable/c/3958b9c34c2729597e182cc606cc43942fd19f7c |
