| 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-2024-35803: x86/efistub: Call mixed mode boot services on the firmware's stack |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| x86/efistub: Call mixed mode boot services on the firmware's stack |
| |
| Normally, the EFI stub calls into the EFI boot services using the stack |
| that was live when the stub was entered. According to the UEFI spec, |
| this stack needs to be at least 128k in size - this might seem large but |
| all asynchronous processing and event handling in EFI runs from the same |
| stack and so quite a lot of space may be used in practice. |
| |
| In mixed mode, the situation is a bit different: the bootloader calls |
| the 32-bit EFI stub entry point, which calls the decompressor's 32-bit |
| entry point, where the boot stack is set up, using a fixed allocation |
| of 16k. This stack is still in use when the EFI stub is started in |
| 64-bit mode, and so all calls back into the EFI firmware will be using |
| the decompressor's limited boot stack. |
| |
| Due to the placement of the boot stack right after the boot heap, any |
| stack overruns have gone unnoticed. However, commit |
| |
| 5c4feadb0011983b ("x86/decompressor: Move global symbol references to C code") |
| |
| moved the definition of the boot heap into C code, and now the boot |
| stack is placed right at the base of BSS, where any overruns will |
| corrupt the end of the .data section. |
| |
| While it would be possible to work around this by increasing the size of |
| the boot stack, doing so would affect all x86 systems, and mixed mode |
| systems are a tiny (and shrinking) fraction of the x86 installed base. |
| |
| So instead, record the firmware stack pointer value when entering from |
| the 32-bit firmware, and switch to this stack every time a EFI boot |
| service call is made. |
| |
| The Linux kernel CVE team has assigned CVE-2024-35803 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Fixed in 6.1.84 with commit 2149f8a56e2ed345c7a4d022a79f6b8fc53ae926 |
| Fixed in 6.6.24 with commit 930775060ca348b8665f60eef14b204172d14f31 |
| Fixed in 6.7.12 with commit fba7ee7187581b5bc222003e73e2592b398bb06d |
| Fixed in 6.8.3 with commit 725351c036452b7db5771a7bed783564bc4b99cc |
| Fixed in 6.9 with commit cefcd4fe2e3aaf792c14c9e56dab89e3d7a65d02 |
| |
| 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-2024-35803 |
| 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/boot/compressed/efi_mixed.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/2149f8a56e2ed345c7a4d022a79f6b8fc53ae926 |
| https://git.kernel.org/stable/c/930775060ca348b8665f60eef14b204172d14f31 |
| https://git.kernel.org/stable/c/fba7ee7187581b5bc222003e73e2592b398bb06d |
| https://git.kernel.org/stable/c/725351c036452b7db5771a7bed783564bc4b99cc |
| https://git.kernel.org/stable/c/cefcd4fe2e3aaf792c14c9e56dab89e3d7a65d02 |
