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b=itfP10JP+qQQFYRwICgghrSyytaSdyLXCGKZ9Vl8+RPLqUt9osqh0lo5z3gnB/VWQ5 irc+VOHg0nFtEMPIq/m67X3rmL98++erTbRYyBUoKEXxAUyICT+2Wub1dzKyZGO9MAAO Nc3V19V0R/vyK/9fuD23Mm2bqcpqjw0LImk/BYGCr17Kgkz2k3Yr09ZWIAIc5UCsI905 p2xwKRHug92TxC3g9awk+y0DYJs4k0gMMVIEjXWo5o39vWcZKdzx8QF/welXPur/W3e+ u8yB0MbZUs+UGxvF/y4RMJHzuOXRL5F0JYxhkgu0BZkUGNR/3SlPqvT/nCGXMZnyoc2m KjtA== X-Forwarded-Encrypted: i=1; AKwUvByxUQhKbdjT8qcXtTOCRUJcfoyW+9VMu3I/PiW5jrN4P4av0BQItnuv0y/89kdUPCFhTwCOxk00vw==@vger.kernel.org X-Gm-Message-State: AFq9FYJ/iPzDlZe2Fi1prn3Z4ZGNiBowRKDsiu4L38po4NBi790oY2QS 3BK/QwNjxFRWadnwpFc6QycJwF1a2tXJFeb+gHLFQWpKPth9Mae0m4lDgxZPtFRORfKngOd3M1t H7TBpDmLGiX8QhEaOOTivqw== X-Received: from pjbee5.prod.google.com ([2002:a17:90a:fc45:b0:3ad:f864:f94f]) (user=jthoughton job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:4d8c:b0:3ac:a521:95e with SMTP id 98e67ed59e1d1-3adead4f7ebmr6876350a91.47.1793051572060; Mon, 26 Oct 2026 14:52:52 -0700 (PDT) Date: Mon, 26 Oct 2026 21:52:21 +0000 In-Reply-To: <20261026215226.3713941-1-jthoughton@google.com> X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Mime-Version: 1.0 References: <20261026215226.3713941-1-jthoughton@google.com> X-Mailer: git-send-email 2.56.0.307.g5fe7bd680c-goog Message-ID: <20261026215226.3713941-6-jthoughton@google.com> Subject: [RFC PATCH 05/10] perf/core: Don't unwind the user stack without an mm From: James Houghton To: Andrew Morton , Alexander Viro Cc: Thomas Gleixner , Peter Zijlstra , Kees Cook , Arnd Bergmann , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Sean Christopherson , Paolo Bonzini , Jim Mattson , Jens Axboe , Pavel Begunkov , "James E.J. Bottomley" , "Martin K. Petersen" , David Sterba , Chris Mason , Alexei Starovoitov , Daniel Borkmann , John Fastabend , Josh Poimboeuf , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, kvm@vger.kernel.org, io-uring@vger.kernel.org, linux-scsi@vger.kernel.org, linux-btrfs@vger.kernel.org, bpf@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, James Houghton Content-Type: text/plain; charset="UTF-8" get_perf_callchain() only checks is_user_task(current) when the regs it is given aren't user mode regs. However, BPF's bpf_get_task_stack() (and bpf_get_task_stack_sleepable()) pass task_pt_regs(current) when called on the current task, which are user mode regs for a user task, even if that task has already gone through exit_mm(), e.g. when called from a program attached to exit_files() or to the dying task's final sched_switch. perf_callchain_user() then unwinds the user stack without an mm. That access does not reliably fail: the user half of the address space belongs to whatever mm happens to be lazily loaded, if any, so the unwinder may read another task's memory. This affects e.g. arm64, riscv, loongarch and csky, whose perf_callchain_user() doesn't check current->mm itself. perf events themselves are not affected, as perf_callchain() already clears the user callchain request when current is not a user task with an mm. Check is_user_task(current) regardless of the regs' mode. Fixes: fa28dcb82a38 ("bpf: Introduce helper bpf_get_task_stack()") Signed-off-by: James Houghton --- kernel/events/callchain.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c index 9d24b6e0c91f..a451ca2a5573 100644 --- a/kernel/events/callchain.c +++ b/kernel/events/callchain.c @@ -245,11 +245,15 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user, } if (user && !crosstask) { - if (!user_mode(regs)) { - if (!is_user_task(current)) - goto exit_put; + /* + * Even if @regs are user mode regs, e.g. task_pt_regs(current) + * passed in by bpf_get_task_stack(), current may already have + * gone through exit_mm(). + */ + if (!is_user_task(current)) + goto exit_put; + if (!user_mode(regs)) regs = task_pt_regs(current); - } if (defer_cookie) { /* -- 2.56.0.307.g5fe7bd680c-goog