Hi,

It is obvious a conflict between the code and the comment. The function aarch64_insn_is_steppable is used to check if a mrs instruction can be safe in single-stepping environment, in the comment it says only reading DAIF bits by mrs is safe in single-stepping environment, and other mrs instructions are not. So aarch64_insn_is_steppable should returen "TRUE" if the mrs instruction being single stepped is reading DAIF bits.

And have verified using a kprobe kernel module which reads the DAIF bits by function arch_local_irq_save with offset setting to 0x4, confirmed that without this modification, it encounters "kprobe_init: register_kprobe failed, returned -22" error while inserting the kprobe kernel module. and with this modification, it can read the DAIF bits in single-stepping environment.

Fixes: 2dd0e8d2d2a1 ("arm64: Kprobes with single stepping support") Cc: stable@vger.kernel.org Signed-off-by: Yiren Xie 1534428646@qq.com

---

arch/arm64/kernel/probes/decode-insn.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/probes/decode-insn.c b/arch/arm64/kernel/probes/decode-insn.c index 6438bf62e753..22383eb1c22c 100644 --- a/arch/arm64/kernel/probes/decode-insn.c +++ b/arch/arm64/kernel/probes/decode-insn.c @@ -40,7 +40,7 @@ static bool __kprobes aarch64_insn_is_steppable(u32 insn) */ if (aarch64_insn_is_mrs(insn)) return aarch64_insn_extract_system_reg(insn)

• 	     != AARCH64_INSN_SPCLREG_DAIF;
  

• 	     == AARCH64_INSN_SPCLREG_DAIF;
  
  

  /*

  • The HINT instruction is steppable only if it is in whitelist

-- 2.34.1

Thanks to correct me. yes the comments seem conflict.

However, I couldn't agree to this change. As I mention in last, when single-step runs, all DAIF bits set, so, the result of reading DAIF is different between before install kprobe and after. Also, I think reading some sys_reg in single-step seems ok (i.e. SYS_MIDR_EL1).

Therefore, allowing only install kprobe on DAIF reading doesn't seem correct.

Thanks