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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