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 [...] Fixes: 20002ded4d93 ("perf_counter: powerpc: Add callchain support") Signed-off-by: Viktor Malik --- arch/powerpc/perf/callchain_32.c | 3 +++ arch/powerpc/perf/callchain_64.c | 3 +++ 2 files changed, 6 insertions(+) diff --git a/arch/powerpc/perf/callchain_32.c b/arch/powerpc/perf/callchain_32.c index ddcc2d8aa64a..b46e21679566 100644 --- a/arch/powerpc/perf/callchain_32.c +++ b/arch/powerpc/perf/callchain_32.c @@ -144,6 +144,9 @@ void perf_callchain_user_32(struct perf_callchain_entry_ctx *entry, sp = regs->gpr[1]; perf_callchain_store(entry, next_ip); + if (!current->mm) + return; + while (entry->nr < entry->max_stack) { fp = (unsigned int __user *) (unsigned long) sp; if (invalid_user_sp(sp) || read_user_stack_32(fp, &next_sp)) diff --git a/arch/powerpc/perf/callchain_64.c b/arch/powerpc/perf/callchain_64.c index 115d1c105e8a..eaaadd6fa81b 100644 --- a/arch/powerpc/perf/callchain_64.c +++ b/arch/powerpc/perf/callchain_64.c @@ -79,6 +79,9 @@ void perf_callchain_user_64(struct perf_callchain_entry_ctx *entry, sp = regs->gpr[1]; perf_callchain_store(entry, next_ip); + if (!current->mm) + return; + while (entry->nr < entry->max_stack) { fp = (unsigned long __user *) sp; if (invalid_user_sp(sp) || read_user_stack_64(fp, &next_sp)) -- 2.53.0