Описание
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.
A flaw was found in the Linux kernel. A local user can exploit a vulnerability in the perf subsystem on AMD processors utilizing the Branch Sampling (BRS) feature. This flaw occurs because the software filtering mechanism for branch records only validates the branch-to address, leaving the branch-from address unchecked. This oversight allows kernel addresses to be exposed to user space, leading to information disclosure.
Отчет
A moderate-impact information disclosure flaw was found in the Linux kernel perf subsystem on AMD processors that support the Branch Sampling (BRS) feature (Zen 3). BRS provides no hardware branch filtering, so privilege-level filtering is performed entirely in software; however, the amd_brs_match_plm() filter only validated the branch-to address against the requested privilege levels. As a result, a local user requesting a user-only branch stack (PERF_SAMPLE_BRANCH_USER) could still receive branch records that originate in the kernel, such as SYSRET or interrupt returns, exposing kernel addresses to user space. This disclosure can weaken KASLR and aid exploitation of other local kernel vulnerabilities, but does not by itself cause memory corruption or privilege escalation. The vulnerable code is present in Red Hat Enterprise Linux 8 (from 8.8 onward), Red Hat Enterprise Linux 9 (from 9.2 onward), Red Hat Enterprise Linux 10, and Red Hat In-Vehicle OS kernel streams; Red Hat Enterprise Linux 6, 7, 8.4, and 8.6 are not affected because the vulnerable code is not present in those streams. For the affected streams the fix is currently deferred: triggering the flaw requires local access and the ability to use perf branch sampling, and the outcome is limited to kernel address disclosure, so remediation is deferred to a future update and the residual risk is exposure of kernel addresses that could assist a KASLR bypass on affected AMD Zen 3 systems.
Меры по смягчению последствий
The flaw can only be triggered through perf branch sampling on AMD processors that support BRS (Zen 3). Unprivileged access to perf events can be restricted by raising the kernel.perf_event_paranoid sysctl to a restrictive value (for example 'sysctl -w kernel.perf_event_paranoid=3', persisted under /etc/sysctl.d/), or by ensuring unprivileged users do not hold perf-related capabilities such as CAP_PERFMON. These measures prevent unprivileged local users from requesting the branch samples through which kernel addresses are leaked.
Затронутые пакеты
| Платформа | Пакет | Состояние | Рекомендация | Релиз |
|---|---|---|---|---|
| Red Hat Enterprise Linux 10 | kernel | Fix deferred | ||
| Red Hat Enterprise Linux 6 | kernel | Not affected | ||
| Red Hat Enterprise Linux 7 | kernel | Not affected | ||
| Red Hat Enterprise Linux 7 | kernel-rt | Not affected | ||
| Red Hat Enterprise Linux 8 | kernel | Fix deferred | ||
| Red Hat Enterprise Linux 8 | kernel-rt | Fix deferred | ||
| Red Hat Enterprise Linux 9 | kernel | Fix deferred | ||
| Red Hat Enterprise Linux 9 | kernel-rt | Fix deferred |
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Дополнительная информация
Статус:
EPSS
5.5 Medium
CVSS3
Связанные уязвимости
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 l...
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 ad
In the Linux kernel, the following vulnerability has been resolved: p ...
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...
EPSS
5.5 Medium
CVSS3