Messages in this thread | | | Subject | Re: [PATCH v2] arm64: add the printing of tpidr_elx in __show_regs() | From | "Leizhen (ThunderTown)" <> | Date | Fri, 29 Apr 2022 12:16:48 +0800 |
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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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