CVE-2021-47430

/// Technical 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

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References