CVE-2025-21632

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Source
https://nvd.nist.gov/vuln/detail/CVE-2025-21632
Import Source
https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2025-21632.json
JSON Data
https://api.test.osv.dev/v1/vulns/CVE-2025-21632
Related
Published
2025-01-19T11:15:08Z
Modified
2025-01-25T23:46:50.955431Z
Summary
[none]
Details

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

x86/fpu: Ensure shadow stack is active before "getting" registers

The x86 shadow stack support has its own set of registers. Those registers are XSAVE-managed, but they are "supervisor state components" which means that userspace can not touch them with XSAVE/XRSTOR. It also means that they are not accessible from the existing ptrace ABI for XSAVE state. Thus, there is a new ptrace get/set interface for it.

The regset code that ptrace uses provides an ->active() handler in addition to the get/set ones. For shadow stack this ->active() handler verifies that shadow stack is enabled via the ARCHSHSTKSHSTK bit in the thread struct. The ->active() handler is checked from some call sites of the regset get/set handlers, but not the ptrace ones. This was not understood when shadow stack support was put in place.

As a result, both the set/get handlers can be called with XFEATURECETUSER in its init state, which would cause getxsaveaddr() to return NULL and trigger a WARNON(). The sspset() handler luckily has an sspactive() check to avoid surprising the kernel with shadow stack behavior when the kernel is not ready for it (ARCHSHSTK_SHSTK==0). That check just happened to avoid the warning.

But the ->get() side wasn't so lucky. It can be called with shadow stacks disabled, triggering the warning in practice, as reported by Christina Schimpe:

WARNING: CPU: 5 PID: 1773 at arch/x86/kernel/fpu/regset.c:198 sspget+0x89/0xa0 [...] Call Trace: <TASK> ? showregs+0x6e/0x80 ? sspget+0x89/0xa0 ? _warn+0x91/0x150 ? sspget+0x89/0xa0 ? reportbug+0x19d/0x1b0 ? handlebug+0x46/0x80 ? excinvalidop+0x1d/0x80 ? asmexcinvalidop+0x1f/0x30 ? _pfxsspget+0x10/0x10 ? sspget+0x89/0xa0 ? sspget+0x52/0xa0 _regsetget+0xad/0xf0 copyregsettouser+0x52/0xc0 ptraceregset+0x119/0x140 ptracerequest+0x13c/0x850 ? waittaskinactive+0x142/0x1d0 ? dosyscall64+0x6d/0x90 arch_ptrace+0x102/0x300 [...]

Ensure that shadow stacks are active in a thread before looking them up in the XSAVE buffer. Since ARCHSHSTKSHSTK and userssp[SHSTKEN] are set at the same time, the active check ensures that there will be something to find in the XSAVE buffer.

[ dhansen: changelog/subject tweaks ]

References

Affected packages

Debian:13 / linux

Package

Name
linux
Purl
pkg:deb/debian/linux?arch=source

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0Unknown introduced version / All previous versions are affected
Fixed
6.12.10-1

Affected versions

6.*

6.1.27-1
6.1.37-1
6.1.38-1
6.1.38-2~bpo11+1
6.1.38-2
6.1.38-3
6.1.38-4~bpo11+1
6.1.38-4
6.1.52-1
6.1.55-1~bpo11+1
6.1.55-1
6.1.64-1
6.1.66-1
6.1.67-1
6.1.69-1~bpo11+1
6.1.69-1
6.1.76-1~bpo11+1
6.1.76-1
6.1.82-1
6.1.85-1
6.1.90-1~bpo11+1
6.1.90-1
6.1.94-1~bpo11+1
6.1.94-1
6.1.98-1
6.1.99-1
6.1.106-1
6.1.106-2
6.1.106-3
6.1.112-1
6.1.115-1
6.1.119-1
6.1.123-1
6.1.124-1
6.3.1-1~exp1
6.3.2-1~exp1
6.3.4-1~exp1
6.3.5-1~exp1
6.3.7-1~bpo12+1
6.3.7-1
6.3.11-1
6.4~rc6-1~exp1
6.4~rc7-1~exp1
6.4.1-1~exp1
6.4.4-1~bpo12+1
6.4.4-1
6.4.4-2
6.4.4-3~bpo12+1
6.4.4-3
6.4.11-1
6.4.13-1
6.5~rc4-1~exp1
6.5~rc6-1~exp1
6.5~rc7-1~exp1
6.5.1-1~exp1
6.5.3-1~bpo12+1
6.5.3-1
6.5.6-1
6.5.8-1
6.5.10-1~bpo12+1
6.5.10-1
6.5.13-1
6.6.3-1~exp1
6.6.4-1~exp1
6.6.7-1~exp1
6.6.8-1
6.6.9-1
6.6.11-1
6.6.13-1~bpo12+1
6.6.13-1
6.6.15-1
6.6.15-2
6.7-1~exp1
6.7.1-1~exp1
6.7.4-1~exp1
6.7.7-1
6.7.9-1
6.7.9-2
6.7.12-1~bpo12+1
6.7.12-1
6.8.9-1
6.8.11-1
6.8.12-1~bpo12+1
6.8.12-1
6.9.2-1~exp1
6.9.7-1~bpo12+1
6.9.7-1
6.9.8-1
6.9.9-1
6.9.10-1~bpo12+1
6.9.10-1
6.9.11-1
6.9.12-1
6.10-1~exp1
6.10.1-1~exp1
6.10.3-1
6.10.4-1
6.10.6-1~bpo12+1
6.10.6-1
6.10.7-1
6.10.9-1
6.10.11-1~bpo12+1
6.10.11-1
6.10.12-1
6.11~rc4-1~exp1
6.11~rc5-1~exp1
6.11-1~exp1
6.11.2-1
6.11.4-1
6.11.5-1~bpo12+1
6.11.5-1
6.11.6-1
6.11.7-1
6.11.9-1
6.11.10-1~bpo12+1
6.11.10-1
6.12~rc6-1~exp1
6.12.3-1
6.12.5-1
6.12.6-1
6.12.8-1
6.12.9-1~bpo12+1
6.12.9-1
6.12.9-1+alpha

Ecosystem specific 

{
    "urgency": "not yet assigned"
}