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 <[email protected]>
> ---
> 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 <[email protected]>
>
