[PATCH 6.18 176/333] powerpc, perf: Check that current->mm is alive before getting user callchain

Greg Kroah-Hartman
2026-03-17T17:19:35Z

From: Viktor Malik <vmalik@redhat.com>

[ Upstream commit e9bbfb4bfa86c6b5515b868d6982ac60505d7e39 ]

It may happen that mm is already released, which leads to kernel panic.
This adds the NULL check for current->mm, similarly to
commit 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 <vmalik@redhat.com>
Tested-by: Qiao Zhao <qzhao@redhat.com>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Reviewed-by: Saket Kumar Bhaskar <skb99@linux.ibm.com>
[Maddy: fixed message to avoid checkpatch format style error]
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260309144045.169427-1-vmalik@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 26aa26482c9ac..992cc5c982144 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 ddcc2d8aa64a5..0de21c5d272c2 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 115d1c105e8a8..30fb61c5f0cb0 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;
--
2.51.0