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CVE-2026-46063x86/shstk: Prevent deadlock during shstk sigreturn

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 if anything grabbed an mmap write lock in between and could have changed the VMA. These mmap_lock_speculate_...() helpers use mm::mm_lock_seq, which is only available when PER_VMA_LOCK is configured. So make X86_USER_SHADOW_STACK depend on it. On x86, PER_VMA_LOCK is a default configuration for SMP kernels. So drop support for the other configs under the assumption that the !SMP shadow stack user base does not exist. Currently there is a check that skips the lookup work when the SSP can be assumed to be on a shadow stack. While reorganizing the function, remove the optimization to make the tricky code flows more common, such that issues like this cannot escape detection for so long.

Timeline

  1. ID reserved

    By Linux

  2. · 14 days later

    Published

  3. · 5 months later

    Record updated

Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.

Scores

CVSS scores of CVE-2026-46063, by who scored it
Scored byCVSSScoreVector
NVDNVD · Analyzed3.1Medium5.5CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
EPSS (exploitation in 30 days)
0.09% · top 99% of all CVEs (14 Nov 2026)
CISA SSVC
Exploitation: none · Automatable: no · Technical impact: partial
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.5.

Affected products

  • Linux · Linux

    • affected 7fad2a432cd35bbf104d2d9d426e74902f22aa95 – < e2c2b044458cbf22da05264fa707308e8d4f86f9
    • affected 7fad2a432cd35bbf104d2d9d426e74902f22aa95 – < d042d69b417515959e49021fef008c9b04a99bd5
    • affected 7fad2a432cd35bbf104d2d9d426e74902f22aa95 – < 4f3374c990fb2adec06d20fd6d780927811c9aa0
    • affected 7fad2a432cd35bbf104d2d9d426e74902f22aa95 – < 3d29db827502067626062f5c74dd502d14ab15bc
    • affected 7fad2a432cd35bbf104d2d9d426e74902f22aa95 – < 9874b2917b9fbc30956fee209d3c4aa47201c64e

  • Linux · Linux

    • affected 6.6
    • unaffected < 6.6
    • unaffected 6.6.140 – ≤ 6.6.*
    • unaffected 6.12.88 – ≤ 6.12.*
    • unaffected 6.18.27 – ≤ 6.18.*
    • unaffected 7.0.4 – ≤ 7.0.*
    • unaffected 7.1 – ≤ *

References

References5

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .