arm64/fpsimd: signal: Forbid non-streaming SVE payload on SME-only systems
Summary
| CVE | CVE-2026-98745 |
|---|---|
| State | PUBLISHED |
| Assigner | Linux |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-10-18 16:17:28 UTC |
| Updated | 2026-10-21 13:21:42 UTC |
| Description | In the Linux kernel, the following vulnerability has been resolved: arm64/fpsimd: signal: Forbid non-streaming SVE payload on SME-only systems When system_supports_sme() is true but system_supports_sve() is false, restoring a specifically crafted SVE signal context can result in the task erroneously having non-streaming SVE state. Subsequent attempts to manipulate the task's FPSIMD/SVE/SME state can result in a variety of problems, including fatal EL1 UNDEFs. In such configurations, the kernel always creates an SVE signal context when delivering a signal, and this can only be in one of two states: (1) SVE_SIG_FLAG_SM is set, and an SVE payload is present containing streaming mode SVE state. The recorded VL is the task's live streaming VL. (2) SVE_SIG_FLAG_SM is clear, and an SVE payload is not present. The FPSIMD context contains the non-streaming mode FPSIMD state. The recorded VL is 0. Currently restore_sve_fpsimd_context() correctly rejects cases where SVE_SIG_FLAG_SM is set and an SVE payload is not present, but fails to reject cases where SVE_SIG_FLAG_SM is clear and an SVE payload is present. Consequently, restore_sve_fpsimd_context() can place the task in a state where it has non-streaming SVE state even when this is not supported by HW. For example, this can cause a later EL1 UNDEF when the kernel attempts to restore the task's ZCR_EL1 value: | # ./sme-sigcontext-to-sve | Internal error: Oops - Undefined instruction: 0000000002000000 [#1] SMP | Modules linked in: | CPU: 0 UID: 0 PID: 131 Comm: sme-sigcontext- Not tainted 7.3.0-rc1 #1 PREEMPT | Hardware name: linux,dummy-virt (DT) | pstate: 61402009 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--) | pc : fpsimd_restore_current_state+0x258/0x458 | lr : exit_to_user_mode_loop+0xb8/0x188 | sp : ffff80008056be40 | x29: ffff80008056be40 x28: fff00000c1670000 x27: 0000000000000000 | x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000 | x23: ffff80008056bec0 x22: 0000000000000008 x21: 0000000000000040 | x20: 0000000000000081 x19: 0000000008800010 x18: 0000000000000000 | x17: 0000fffffd412570 x16: 0000000000001000 x15: 0000fffffd4123b0 | x14: 0000fffffd412780 x13: 0000fffffd412be8 x12: 0000000047435300 | x11: 0000fffffd412570 x10: 0000000000000000 x9 : 0000000045585401 | x8 : fff00000c18a6c44 x7 : 0000000000000000 x6 : 0000000000000002 | x5 : 0000000000000002 x4 : ffff800080568000 x3 : 0000000000000001 | x2 : 0000000008800010 x1 : fff00000c1670000 x0 : 0000000008800000 | Call trace: | fpsimd_restore_current_state+0x258/0x458 (P) | exit_to_user_mode_loop+0xb8/0x188 | el0_svc+0x1cc/0x1d0 | el0t_64_sync_handler+0xa0/0xe4 | el0t_64_sync+0x198/0x19c | Code: d5384101 f9400020 53175c03 36b80de0 (d5381202) | ---[ end trace 0000000000000000 ]--- | Kernel panic - not syncing: Oops - Undefined instruction: Fatal exception in interrupt | Kernel Offset: 0x291fb1000000 from 0xffff800080000000 | PHYS_OFFSET: 0x40000000 | CPU features: 0x0,00000000,0052802f,ffb88f43,3afcf73f | Memory Limit: none Rework restore_sve_fpsimd_context() to reject cases where SVE_SIG_FLAG_SM is clear and an SVE payload is not present. As parse_user_sigframe() rejects SVE signal frames when neither SVE nor SME are supported, it isn't necessary for restore_sve_fpsimd_context() to handle the case where neither are supported. |
Risk And Classification
EPSS: 0.001680000 probability, percentile 0.057240000 (date 2026-10-21)
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Linux | Linux | affected 7dde62f0687c8856b6c0660066c7ee83a6a6f033 052acee9880114879b5c221fc8dad69b786d0938 git | Not specified |
| CNA | Linux | Linux | affected 7dde62f0687c8856b6c0660066c7ee83a6a6f033 f2338929c7663859c0c74dd6fef2c0245066f845 git | Not specified |
| CNA | Linux | Linux | affected 7dde62f0687c8856b6c0660066c7ee83a6a6f033 2bce6f006cfe0b60e8249fd8d51396d99355cba3 git | Not specified |
| CNA | Linux | Linux | affected 7dde62f0687c8856b6c0660066c7ee83a6a6f033 88c1c611552b24658eb61244086691c02be2013b git | Not specified |
| CNA | Linux | Linux | affected 7dde62f0687c8856b6c0660066c7ee83a6a6f033 e060d9069b49fe55f38057dfe592068014652671 git | Not specified |
| CNA | Linux | Linux | affected 05458ee3ff82b31a4564836a84ef20d6c233dfc7 git | Not specified |
| CNA | Linux | Linux | affected 6.1.7 6.2 semver | Not specified |
| CNA | Linux | Linux | affected 6.2 | Not specified |
| CNA | Linux | Linux | unaffected 6.2 semver | Not specified |
| CNA | Linux | Linux | unaffected 6.6.160 6.6.* semver | Not specified |
| CNA | Linux | Linux | unaffected 6.12.113 6.12.* semver | Not specified |
| CNA | Linux | Linux | unaffected 6.18.56 6.18.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.2.10 7.2.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.3 * original_commit_for_fix | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| git.kernel.org/stable/c/88c1c611552b24658eb61244086691c02be2013b | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/052acee9880114879b5c221fc8dad69b786d0938 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/f2338929c7663859c0c74dd6fef2c0245066f845 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/2bce6f006cfe0b60e8249fd8d51396d99355cba3 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/e060d9069b49fe55f38057dfe592068014652671 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.