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Date: Thu, 29 Feb 2024 06:43:19 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: gregkh@...nel.org
Subject: CVE-2023-52476: perf/x86/lbr: Filter vsyscall addresses

From: gregkh@...nel.org

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

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

perf/x86/lbr: Filter vsyscall addresses

We found that a panic can occur when a vsyscall is made while LBR sampling
is active. If the vsyscall is interrupted (NMI) for perf sampling, this
call sequence can occur (most recent at top):

    __insn_get_emulate_prefix()
    insn_get_emulate_prefix()
    insn_get_prefixes()
    insn_get_opcode()
    decode_branch_type()
    get_branch_type()
    intel_pmu_lbr_filter()
    intel_pmu_handle_irq()
    perf_event_nmi_handler()

Within __insn_get_emulate_prefix() at frame 0, a macro is called:

    peek_nbyte_next(insn_byte_t, insn, i)

Within this macro, this dereference occurs:

    (insn)->next_byte

Inspecting registers at this point, the value of the next_byte field is the
address of the vsyscall made, for example the location of the vsyscall
version of gettimeofday() at 0xffffffffff600000. The access to an address
in the vsyscall region will trigger an oops due to an unhandled page fault.

To fix the bug, filtering for vsyscalls can be done when
determining the branch type. This patch will return
a "none" branch if a kernel address if found to lie in the
vsyscall region.

The Linux kernel CVE team has assigned CVE-2023-52476 to this issue.


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

	Fixed in 5.15.137 with commit 403d201d1fd1
	Fixed in 6.1.59 with commit 386398949765
	Fixed in 6.5.8 with commit f71edacbd4f9
	Fixed in 6.6 with commit e53899771a02

Please see https://www.kernel.org or 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-2023-52476
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/utils.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/403d201d1fd144cb249836dafb222f6375871c6c
	https://git.kernel.org/stable/c/3863989497652488a50f00e96de4331e5efabc6c
	https://git.kernel.org/stable/c/f71edacbd4f99c0e12fe4a4007ab4d687d0688db
	https://git.kernel.org/stable/c/e53899771a02f798d436655efbd9d4b46c0f9265

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