From: "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
To: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>,
"James Morse" <james.morse@arm.com>
Subject: Re: [PATCH v2] arm64: add the printing of tpidr_elx in __show_regs()
Date: Fri, 29 Apr 2022 12:16:48 +0800 [thread overview]
Message-ID: <c06c15c1-5c8e-2d03-4fbc-c8e5a5dff956@huawei.com> (raw)
In-Reply-To: <20220428131259.GA14810@willie-the-truck>
On 2022/4/28 21:13, Will Deacon wrote:
> On Thu, Apr 28, 2022 at 08:03:50PM +0800, Leizhen (ThunderTown) wrote:
>>
>>
>> On 2022/4/28 19:07, Leizhen (ThunderTown) wrote:
>>>
>>>
>>> On 2022/4/28 18:21, Will Deacon wrote:
>>>> On Wed, Mar 16, 2022 at 02:24:08PM +0800, Zhen Lei wrote:
>>>>> Commit 7158627686f0 ("arm64: percpu: implement optimised pcpu access
>>>>> using tpidr_el1") and commit 6d99b68933fb ("arm64: alternatives: use
>>>>> tpidr_el2 on VHE hosts") use tpidr_elx to cache my_cpu_offset to optimize
>>>>> pcpu access. However, when performing reverse execution based on the
>>>>> registers and the memory contents in kdump, this information is sometimes
>>>>> required if there is a pcpu access.
>>>>>
>>>>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>>>>> ---
>>>>> arch/arm64/kernel/process.c | 11 +++++++++++
>>>>> 1 file changed, 11 insertions(+)
>>>>>
>>>>> v1 --> v2:
>>>>> Directly print the tpidr_elx register of the current exception level.
>>>>> Avoid coupling with the implementation of 'my_cpu_offset'.
>>>>>
>>>>> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
>>>>> index 5369e649fa79ff8..738932e6fa4e947 100644
>>>>> --- a/arch/arm64/kernel/process.c
>>>>> +++ b/arch/arm64/kernel/process.c
>>>>> @@ -216,6 +216,17 @@ void __show_regs(struct pt_regs *regs)
>>>>> show_regs_print_info(KERN_DEFAULT);
>>>>> print_pstate(regs);
>>>>>
>>>>> + switch (read_sysreg(CurrentEL)) {
>>>>
>>>> This should use is_kernel_in_hyp_mode() to detect if we're running at El2.
>>
>> static inline bool is_kernel_in_hyp_mode(void)
>> {
>> return read_sysreg(CurrentEL) == CurrentEL_EL2;
>> }
>>
>> I think it's more intuitive to use "switch (read_sysreg(CurrentEL))".
>
> No, I disagree with you here, sorry.
OK. Change it to the following form in v3?
+ if (is_kernel_in_hyp_mode())
+ printk("tpidr_el2 : %016llx\n", read_sysreg(TPIDR_EL2));
+ else
+ printk("tpidr_el1 : %016llx\n", read_sysreg(TPIDR_EL1));
By the way, Is there a requirement on the case of register names?
I see some use TPIDR_EL1 and some use tpidr_el1.
>
>>>>> + case CurrentEL_EL1:
>>>>> + printk("tpidr_el1 : %016llx\n", read_sysreg(TPIDR_EL1));
>>>>> + break;
>>>>> + case CurrentEL_EL2:
>>>>> + printk("tpidr_el2 : %016llx\n", read_sysreg(TPIDR_EL2));
>>>>> + break;
>>>>> + default:
>>>>> + break;
>>>>> + }
>>>>
>>>> I think this path can be triggered directly from usermode, so we really
>>>> shouldn't be printing raw kernel virtual addresses here.
>>>
>>> I run echo c > /proc/sysrq-trigger and didn't trigger this path, but maybe
>>> there's another way. Analysis from the other side, except for the instruction
>>> address, all generic registers r0-r31 is output as raw. There's also an
>>> opportunity to contain the instruction address.
>>
>> On second thought, there seemed to be nothing wrong with it. The user need
>> to have capable() first. Then the address of the perpcu memory is not static,
>> the memory is dynamically allocated, exposing it is no different than exposing sp.
>
> If show_unhandled_signals is set, then I think any fatal signal takes this
> path, no?
I looked at the implementation of arm64_show_signal(), and there must be a
chance to take this path. But last night, I came to my senses, the value
stored in tpidr is actually an offset, not an address. So there should be
no kernel address leakage problem.
>
> Will
> .
>
--
Regards,
Zhen Lei
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prev parent reply other threads:[~2022-04-29 4:18 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-16 6:24 [PATCH v2] arm64: add the printing of tpidr_elx in __show_regs() Zhen Lei
2022-04-27 18:40 ` Catalin Marinas
2022-04-28 10:23 ` Will Deacon
2022-04-28 10:21 ` Will Deacon
2022-04-28 11:07 ` Leizhen (ThunderTown)
2022-04-28 12:03 ` Leizhen (ThunderTown)
2022-04-28 12:10 ` Leizhen (ThunderTown)
2022-04-28 13:13 ` Will Deacon
2022-04-29 4:16 ` Leizhen (ThunderTown) [this message]
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