CVE-2026-46063

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

x86/shstk: Prevent deadlock during shstk sigreturn

During sigreturn the shadow stack signal frame is popped. The kernel does

this by reading the shadow stack using normal read accesses. When it can't

assume the memory is shadow stack, it takes extra steps to makes sure it is

reading actual shadow stack memory and not other normal readable memory. It

does this by holding the mmap read lock while doing the access and checking

the flags of the VMA.

Unfortunately that is not safe. If the read of the shadow stack sigframe

hits a page fault, the fault handler will try to recursively grab another

mmap read lock. This normally works ok, but if a writer on another CPU is

also waiting, the second read lock could fail and cause a deadlock.

Fix this by not holding mmap lock during the read access to userspace.

Instead use mmap_lock_speculate_...() to watch for changes between dropping

mmap lock and the userspace access. Retry

/// 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