CVE-2026-72237: perf/x86/amd/brs: Fix kernel address leakage

CVE-2026-72237: perf/x86/amd/brs: Fix kernel address leakage

[Greg Kroah-Hartman]

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

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

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

perf/x86/amd/brs: Fix kernel address leakage

A user-only branch stack can contain branches that originate from
the kernel. As a result, kernel addresses are exposed to user space
even when PERF_SAMPLE_BRANCH_USER is requested. On AMD processors
supporting X86_FEATURE_BRS (Zen 3 only), perf can still report entries
such as SYSRET/interrupt returns for which the branch-from addresses
are in the kernel.

E.g.

  $ perf record -j any,u -c 4000 -e branch-brs -o - -- \
        perf bench syscall basic --loop 1000 | \
        perf script -i - -F brstack|tr ' ' '\n'| \
        grep -E '0x[89a-f][0-9a-f]{15}'

  ...
  0xffffffff810001c4/0x72e2e32955eb/-/-/-/0//-
  0xffffffff810001c4/0x72e2d94a9821/-/-/-/0//-
  0xffffffff810001c4/0x72e2d94ffa1b/-/-/-/0//-
  ...

BRS provides no hardware branch filtering, so privilege level
filtering is performed entirely in software. However, amd_brs_match_plm()
only validates the branch-to address against the requested privilege
levels. For branches from the kernel to user space, the branch-from
address is left unchecked and is leaked. Extend the software filter to
also validate the branch-from address, so that any branch record whose
branch-from address is in the kernel is dropped when
PERF_SAMPLE_BRANCH_USER is requested.

The Linux kernel CVE team has assigned CVE-2026-72237 to this issue.


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

	Issue introduced in 5.19 with commit 8910075d61a37e5b0d82e6c83ed9a0a31fe9ea08 and fixed in 6.6.145 with commit ac44b4a3d6137489f8fa2e794b12e849c6b22eaa
	Issue introduced in 5.19 with commit 8910075d61a37e5b0d82e6c83ed9a0a31fe9ea08 and fixed in 6.12.97 with commit 90843d00dbc61220b66408ea0d8775cae9e51f70
	Issue introduced in 5.19 with commit 8910075d61a37e5b0d82e6c83ed9a0a31fe9ea08 and fixed in 6.18.40 with commit 046f6244da9b68e463a849b21446b9424e531491
	Issue introduced in 5.19 with commit 8910075d61a37e5b0d82e6c83ed9a0a31fe9ea08 and fixed in 7.1.5 with commit 2e706be56f418718bb3ae66c0aa94f9b61150e6d
	Issue introduced in 5.19 with commit 8910075d61a37e5b0d82e6c83ed9a0a31fe9ea08 and fixed in 7.2-rc3 with commit 47915e855fb38b42133e31ba917d99565f862154

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-2026-72237
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/events/amd/brs.c


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/ac44b4a3d6137489f8fa2e794b12e849c6b22eaa
	https://git.kernel.org/stable/c/90843d00dbc61220b66408ea0d8775cae9e51f70
	https://git.kernel.org/stable/c/046f6244da9b68e463a849b21446b9424e531491
	https://git.kernel.org/stable/c/2e706be56f418718bb3ae66c0aa94f9b61150e6d
	https://git.kernel.org/stable/c/47915e855fb38b42133e31ba917d99565f862154