| Message ID | tencent_9DCAEBDF4D9BCDB4687B502DB6B608E4FB0A@qq.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | arm64: kprobe: fix an error in single stepping support | expand |
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
On Fri, Jan 17, 2025 at 07:57:32AM +0000, Yeoreum Yun wrote: > > 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. Right, the code seems ok. I think we should just remove the comment instead. Will
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