On 27/05/2019 10:39, Yongliang Gao wrote:

harden_branch_predictor() call smp_processor_id() in preemptible context, this would cause a bug messages.

The bug messages is as follows: BUG: using smp_processor_id() in preemptible [00000000] code: syz-executor0/17992 caller is harden_branch_predictor arch/arm/include/asm/system_misc.h:27 [inline] caller is __do_user_fault+0x34/0x114 arch/arm/mm/fault.c:200 CPU: 1 PID: 17992 Comm: syz-executor0 Tainted: G O 4.4.176 #1 Hardware name: Hisilicon A9 [<c0114ae4>] (unwind_backtrace) from [<c010e6fc>] (show_stack+0x18/0x1c) [<c010e6fc>] (show_stack) from [<c0379514>] (dump_stack+0xc8/0x118) [<c0379514>] (dump_stack) from [<c039b5a0>] (check_preemption_disabled+0xf4/0x138) [<c039b5a0>] (check_preemption_disabled) from [<c011abe4>] (__do_user_fault+0x34/0x114) [<c011abe4>] (__do_user_fault) from [<c053b0d0>] (do_page_fault+0x3b4/0x3d8) [<c053b0d0>] (do_page_fault) from [<c01013dc>] (do_DataAbort+0x58/0xf8) [<c01013dc>] (do_DataAbort) from [<c053a880>] (__dabt_usr+0x40/0x60)

Reported-by: Jingwen Qiu qiujingwen@huawei.com Signed-off-by: Yongliang Gao gaoyongliang@huawei.com Cc: stable@vger.kernel.org

---

arch/arm/include/asm/system_misc.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/system_misc.h b/arch/arm/include/asm/system_misc.h index 66f6a3a..4a55cfb 100644 --- a/arch/arm/include/asm/system_misc.h +++ b/arch/arm/include/asm/system_misc.h @@ -22,9 +22,10 @@ static inline void harden_branch_predictor(void) { harden_branch_predictor_fn_t fn = per_cpu(harden_branch_predictor_fn,

• 				  smp_processor_id());
  

• 				  get_cpu());
  

  if (fn) fn();
• put_cpu();

} #else #define harden_branch_predictor() do { } while (0)

This doesn't look like the right fix. If we're in a preemptible context, then we could invalidate the branch predictor on the wrong CPU.

The right fix would be to move the call to a point where we haven't enabled preemption yet.

Thanks,

M.