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Mon, 9 Mar 2026 16:29:51 +0000 (GMT) Date: Mon, 9 Mar 2026 21:59:48 +0530 From: Saket Kumar Bhaskar To: Viktor Malik Cc: linuxppc-dev@lists.ozlabs.org, Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , "Christophe Leroy (CS GROUP)" , Benjamin Herrenschmidt , Paul Mackerras , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH v2] powerpc, perf: Check that current->mm is alive before getting user callchain Message-ID: References: <20260309144045.169427-1-vmalik@redhat.com> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260309144045.169427-1-vmalik@redhat.com> X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzA5MDE0NSBTYWx0ZWRfX+rjeGaeASbO2 DRRCfL+CMorHO5ng1qGUas6J8JvgX5kk/akDTzG+WtfiXrtQPT337K5va/I6ATguS1jUcTGEzH+ 1qUEdOzZBCz8pZoFVqPQE09RWTe9C2CD2iBQySe1f/IjXU2FOEs+WMIyxZ5I/CNi7OUokx7MGRr ftoeP5tRJ1019lbSHRewSQ4jQXpPBJ9y2fZTZMqX2q8ZAZGqYrg4vWJjO9nMmDe884OBye9//WK o7c46o3MbT2VP1NjQ6u82nEMXLKlug+vWoX2qsrw4QH5vXXLzL++Z4Yh0Gor5EnSb0cyyuR3kEK iID65YQcNw8QuqYtIheYBhSBj9GOXivDtq5XhN/2nJ+L2GmR/zX0j49Hz9JiTrOVXdcQpH9L+sn ylSAOQIfC+dyoUZxr2omBDe1CasazDS71d3fBzHIg1hgGZk03AG6po7boYLsp+IK1VRK5fu5VsS u/bMuNFLnc+gZ6v7+Lg== X-Proofpoint-GUID: AykpcraF3vgF-W4mHKIkLrlGlLQPY39P X-Proofpoint-ORIG-GUID: 7ljpo1MiTfY3ZH2wBCg09610OOHkGqxF X-Authority-Analysis: v=2.4 cv=QoFTHFyd c=1 sm=1 tr=0 ts=69aef585 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=kj9zAlcOel0A:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=20KFwNOVAAAA:8 a=VnNF1IyMAAAA:8 a=e-EAHXkKvpEb-08ajsIA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-09_04,2026-03-09_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 spamscore=0 priorityscore=1501 phishscore=0 lowpriorityscore=0 adultscore=0 clxscore=1015 malwarescore=0 suspectscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2602130000 definitions=main-2603090145 On Mon, Mar 09, 2026 at 03:40:45PM +0100, Viktor Malik wrote: > 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 LGTM, feel free to add below tag: Reviewed-by: Saket Kumar Bhaskar >