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Message-ID: <2024040252-CVE-2024-26674-4ff9@gregkh> Date: Tue, 2 Apr 2024 09:01:51 +0200 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-cve-announce@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org> Subject: CVE-2024-26674: x86/lib: Revert to _ASM_EXTABLE_UA() for {get,put}_user() fixups Description =========== In the Linux kernel, the following vulnerability has been resolved: x86/lib: Revert to _ASM_EXTABLE_UA() for {get,put}_user() fixups During memory error injection test on kernels >= v6.4, the kernel panics like below. However, this issue couldn't be reproduced on kernels <= v6.3. mce: [Hardware Error]: CPU 296: Machine Check Exception: f Bank 1: bd80000000100134 mce: [Hardware Error]: RIP 10:<ffffffff821b9776> {__get_user_nocheck_4+0x6/0x20} mce: [Hardware Error]: TSC 411a93533ed ADDR 346a8730040 MISC 86 mce: [Hardware Error]: PROCESSOR 0:a06d0 TIME 1706000767 SOCKET 1 APIC 211 microcode 80001490 mce: [Hardware Error]: Run the above through 'mcelog --ascii' mce: [Hardware Error]: Machine check: Data load in unrecoverable area of kernel Kernel panic - not syncing: Fatal local machine check The MCA code can recover from an in-kernel #MC if the fixup type is EX_TYPE_UACCESS, explicitly indicating that the kernel is attempting to access userspace memory. However, if the fixup type is EX_TYPE_DEFAULT the only thing that is raised for an in-kernel #MC is a panic. ex_handler_uaccess() would warn if users gave a non-canonical addresses (with bit 63 clear) to {get, put}_user(), which was unexpected. Therefore, commit b19b74bc99b1 ("x86/mm: Rework address range check in get_user() and put_user()") replaced _ASM_EXTABLE_UA() with _ASM_EXTABLE() for {get, put}_user() fixups. However, the new fixup type EX_TYPE_DEFAULT results in a panic. Commit 6014bc27561f ("x86-64: make access_ok() independent of LAM") added the check gp_fault_address_ok() right before the WARN_ONCE() in ex_handler_uaccess() to not warn about non-canonical user addresses due to LAM. With that in place, revert back to _ASM_EXTABLE_UA() for {get,put}_user() exception fixups in order to be able to handle in-kernel MCEs correctly again. [ bp: Massage commit message. ] The Linux kernel CVE team has assigned CVE-2024-26674 to this issue. Affected and fixed versions =========================== Issue introduced in 6.4 with commit b19b74bc99b1 and fixed in 6.6.17 with commit 2aed1b6c33af Issue introduced in 6.4 with commit b19b74bc99b1 and fixed in 6.7.5 with commit 2da241c5ed78 Issue introduced in 6.4 with commit b19b74bc99b1 and fixed in 6.8 with commit 8eed4e00a370 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-2024-26674 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/lib/getuser.S arch/x86/lib/putuser.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/2aed1b6c33afd8599d01c6532bbecb829480a674 https://git.kernel.org/stable/c/2da241c5ed78d0978228a1150735539fe1a60eca https://git.kernel.org/stable/c/8eed4e00a370b37b4e5985ed983dccedd555ea9d
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