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Mon, 09 Mar 2026 10:40:57 -0400 X-MC-Unique: V_CeawzUPCSsTTzOUpp3KA-1 X-Mimecast-MFC-AGG-ID: V_CeawzUPCSsTTzOUpp3KA_1773067256 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 919BE18002C9; Mon, 9 Mar 2026 14:40:55 +0000 (UTC) Received: from vmalik-fedora.redhat.com (unknown [10.45.225.182]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C36D0180035F; Mon, 9 Mar 2026 14:40:50 +0000 (UTC) From: Viktor Malik To: linuxppc-dev@lists.ozlabs.org Cc: Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , "Christophe Leroy (CS GROUP)" , Viktor Malik , Benjamin Herrenschmidt , Paul Mackerras , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Saket Kumar Bhaskar Subject: [PATCH v2] powerpc, perf: Check that current->mm is alive before getting user callchain Date: Mon, 9 Mar 2026 15:40:45 +0100 Message-ID: <20260309144045.169427-1-vmalik@redhat.com> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 X-Mimecast-MFC-PROC-ID: CaU2MweukjJDzHGeqATAyFXTYBvOfEFv_zA3p4b-q-c_1773067256 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true It may happen that mm is already released, which leads to kernel panic. This adds the NULL check for current->mm, similarly to 20afc60f892d ("x86, perf: Check that current->mm is alive before getting user callchain"). I was getting this panic when running a profiling BPF program (profile.py from bcc-tools): [26215.051935] Kernel attempted to read user page (588) - exploit attempt? (uid: 0) [26215.051950] BUG: Kernel NULL pointer dereference on read at 0x00000588 [26215.051952] Faulting instruction address: 0xc00000000020fac0 [26215.051957] Oops: Kernel access of bad area, sig: 11 [#1] [...] [26215.052049] Call Trace: [26215.052050] [c000000061da6d30] [c00000000020fc10] perf_callchain_user_64+0x2d0/0x490 (unreliable) [26215.052054] [c000000061da6dc0] [c00000000020f92c] perf_callchain_user+0x1c/0x30 [26215.052057] [c000000061da6de0] [c0000000005ab2a0] get_perf_callchain+0x100/0x360 [26215.052063] [c000000061da6e70] [c000000000573bc8] bpf_get_stackid+0x88/0xf0 [26215.052067] [c000000061da6ea0] [c008000000042258] bpf_prog_16d4ab9ab662f669_do_perf_event+0xf8/0x274 [...] In addition, move storing the top-level stack entry to generic perf_callchain_user to make sure the top-evel entry is always captured, even if current->mm is NULL. Fixes: 20002ded4d93 ("perf_counter: powerpc: Add callchain support") Signed-off-by: Viktor Malik --- Changes in v2: - Move call to perf_callchain_store() for the top-level stack entry to common perf_callchain_user (Saket) arch/powerpc/perf/callchain.c | 5 +++++ arch/powerpc/perf/callchain_32.c | 1 - arch/powerpc/perf/callchain_64.c | 1 - 3 files changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/powerpc/perf/callchain.c b/arch/powerpc/perf/callchain.c index 26aa26482c9a..992cc5c98214 100644 --- a/arch/powerpc/perf/callchain.c +++ b/arch/powerpc/perf/callchain.c @@ -103,6 +103,11 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *re void perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs) { + perf_callchain_store(entry, perf_arch_instruction_pointer(regs)); + + if (!current->mm) + return; + if (!is_32bit_task()) perf_callchain_user_64(entry, regs); else diff --git a/arch/powerpc/perf/callchain_32.c b/arch/powerpc/perf/callchain_32.c index ddcc2d8aa64a..0de21c5d272c 100644 --- a/arch/powerpc/perf/callchain_32.c +++ b/arch/powerpc/perf/callchain_32.c @@ -142,7 +142,6 @@ void perf_callchain_user_32(struct perf_callchain_entry_ctx *entry, next_ip = perf_arch_instruction_pointer(regs); lr = regs->link; sp = regs->gpr[1]; - perf_callchain_store(entry, next_ip); while (entry->nr < entry->max_stack) { fp = (unsigned int __user *) (unsigned long) sp; diff --git a/arch/powerpc/perf/callchain_64.c b/arch/powerpc/perf/callchain_64.c index 115d1c105e8a..30fb61c5f0cb 100644 --- a/arch/powerpc/perf/callchain_64.c +++ b/arch/powerpc/perf/callchain_64.c @@ -77,7 +77,6 @@ void perf_callchain_user_64(struct perf_callchain_entry_ctx *entry, next_ip = perf_arch_instruction_pointer(regs); lr = regs->link; sp = regs->gpr[1]; - perf_callchain_store(entry, next_ip); while (entry->nr < entry->max_stack) { fp = (unsigned long __user *) sp; -- 2.53.0