linux-cve-announce - CVE-2025-38033: x86/Kconfig: make CFI_AUTO

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Message-ID: <2025061825-CVE-2025-38033-8da2@gregkh>
Date: Wed, 18 Jun 2025 11:33:29 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38033: x86/Kconfig: make CFI_AUTO_DEFAULT depend on !RUST or Rust >= 1.88

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

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

x86/Kconfig: make CFI_AUTO_DEFAULT depend on !RUST or Rust >= 1.88

Calling core::fmt::write() from rust code while FineIBT is enabled
results in a kernel panic:

[ 4614.199779] kernel BUG at arch/x86/kernel/cet.c:132!
[ 4614.205343] Oops: invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
[ 4614.211781] CPU: 2 UID: 0 PID: 6057 Comm: dmabuf_dump Tainted: G     U     O       6.12.17-android16-0-g6ab38c534a43 #1 9da040f27673ec3945e23b998a0f8bd64c846599
[ 4614.227832] Tainted: [U]=USER, [O]=OOT_MODULE
[ 4614.241247] RIP: 0010:do_kernel_cp_fault+0xea/0xf0
...
[ 4614.398144] RIP: 0010:_RNvXs5_NtNtNtCs3o2tGsuHyou_4core3fmt3num3impyNtB9_7Display3fmt+0x0/0x20
[ 4614.407792] Code: 48 f7 df 48 0f 48 f9 48 89 f2 89 c6 5d e9 18 fd ff ff 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 41 81 ea 14 61 af 2c 74 03 0f 0b 90 <66> 0f 1f 00 55 48 89 e5 48 89 f2 48 8b 3f be 01 00 00 00 5d e9 e7
[ 4614.428775] RSP: 0018:ffffb95acfa4ba68 EFLAGS: 00010246
[ 4614.434609] RAX: 0000000000000000 RBX: 0000000000000010 RCX: 0000000000000000
[ 4614.442587] RDX: 0000000000000007 RSI: ffffb95acfa4ba70 RDI: ffffb95acfa4bc88
[ 4614.450557] RBP: ffffb95acfa4bae0 R08: ffff0a00ffffff05 R09: 0000000000000070
[ 4614.458527] R10: 0000000000000000 R11: ffffffffab67eaf0 R12: ffffb95acfa4bcc8
[ 4614.466493] R13: ffffffffac5d50f0 R14: 0000000000000000 R15: 0000000000000000
[ 4614.474473]  ? __cfi__RNvXs5_NtNtNtCs3o2tGsuHyou_4core3fmt3num3impyNtB9_7Display3fmt+0x10/0x10
[ 4614.484118]  ? _RNvNtCs3o2tGsuHyou_4core3fmt5write+0x1d2/0x250

This happens because core::fmt::write() calls
core::fmt::rt::Argument::fmt(), which currently has CFI disabled:

library/core/src/fmt/rt.rs:
171     // FIXME: Transmuting formatter in new and indirectly branching to/calling
172     // it here is an explicit CFI violation.
173     #[allow(inline_no_sanitize)]
174     #[no_sanitize(cfi, kcfi)]
175     #[inline]
176     pub(super) unsafe fn fmt(&self, f: &mut Formatter<'_>) -> Result {

This causes a Control Protection exception, because FineIBT has sealed
off the original function's endbr64.

This makes rust currently incompatible with FineIBT. Add a Kconfig
dependency that prevents FineIBT from getting turned on by default
if rust is enabled.

[ Rust 1.88.0 (scheduled for 2025-06-26) should have this fixed [1],
  and thus we relaxed the condition with Rust >= 1.88.

  When `objtool` lands checking for this with e.g. [2], the plan is
  to ideally run that in upstream Rust's CI to prevent regressions
  early [3], since we do not control `core`'s source code.

  Alice tested the Rust PR backported to an older compiler.

  Peter would like that Rust provides a stable `core` which can be
  pulled into the kernel: "Relying on that much out of tree code is
  'unfortunate'".

    - Miguel ]

[ Reduced splat. - Miguel ]

The Linux kernel CVE team has assigned CVE-2025-38033 to this issue.


Affected and fixed versions
===========================

	Fixed in 6.12.31 with commit 5a8d073d87da4ad1496b35adaee5719e94665d81
	Fixed in 6.14.9 with commit 6b9956d09382bcbd5fd260c4b60ec48680a4cffb
	Fixed in 6.15 with commit 5595c31c370957aabe739ac3996aedba8267603f

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-38033
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	arch/x86/Kconfig


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/5a8d073d87da4ad1496b35adaee5719e94665d81
	https://git.kernel.org/stable/c/6b9956d09382bcbd5fd260c4b60ec48680a4cffb
	https://git.kernel.org/stable/c/5595c31c370957aabe739ac3996aedba8267603f