Re: [PATCH 01/11] Initialize the mapping of KASan shadow memory

From: Liuwenliang (Abbott Liu)
Date: Thu Nov 16 2017 - 09:28:52 EST

On 16/11/17 17:54 Marc Zyngier [mailto:marc.zyngier@xxxxxxx] wrote:
>On Thu, Nov 16 2017 at 3:07:54 am GMT, "Liuwenliang (Abbott Liu)" <liuwenliang@xxxxxxxxxx> wrote:
>>>On 15/11/17 13:16, Liuwenliang (Abbott Liu) wrote:
>>>> On 09/11/17 18:36 Marc Zyngier [mailto:marc.zyngier@xxxxxxx] wrote:
>>>>> On Wed, Nov 15 2017 at 10:20:02 am GMT, "Liuwenliang (Abbott Liu)"
>>>>> <liuwenliang@xxxxxxxxxx> wrote:
>>>>>> diff --git a/arch/arm/include/asm/cp15.h
>>>>>> b/arch/arm/include/asm/cp15.h index dbdbce1..6db1f51 100644
>>>>>> --- a/arch/arm/include/asm/cp15.h
>>>>>> +++ b/arch/arm/include/asm/cp15.h
>>>>>> @@ -64,6 +64,43 @@
>>>>>> #define __write_sysreg(v, r, w, c, t) asm volatile(w " " c : :
>>>>>> "r" ((t)(v)))
>>>>>> #define write_sysreg(v, ...) __write_sysreg(v, __VA_ARGS__)
>>>>>>
>>>>>> +#ifdef CONFIG_ARM_LPAE
>>>>>> +#define TTBR0 __ACCESS_CP15_64(0, c2)
>>>>>> +#define TTBR1 __ACCESS_CP15_64(1, c2)
>>>>>> +#define PAR __ACCESS_CP15_64(0, c7)
>>>>>> +#else
>>>>>> +#define TTBR0 __ACCESS_CP15(c2, 0, c0, 0)
>>>>>> +#define TTBR1 __ACCESS_CP15(c2, 0, c0, 1)
>>>>>> +#define PAR __ACCESS_CP15(c7, 0, c4, 0)
>>>>>> +#endif
>>>>> Again: there is no point in not having these register encodings
>>>>> cohabiting. They are both perfectly defined in the architecture.
>>>>> Just suffix one (or even both) with their respective size, making
>>>>> it obvious which one you're talking about.
>>>>
>>>> I am sorry that I didn't point why I need to define TTBR0/ TTBR1/PAR
>>>> in to different way between CONFIG_ARM_LPAE and non CONFIG_ARM_LPAE.
>>>> The following description is the reason:
>>>> Here is the description come from
>>>> DDI0406C2c_arm_architecture_reference_manual.pdf:
>>>[...]
>>>
>>>You're missing the point. TTBR0 existence as a 64bit CP15 register has
>>>nothing to do the kernel being compiled with LPAE or not. It has
>>>everything to do with the HW supporting LPAE, and it is the kernel's job
>>>to use the right accessor depending on how it is compiled. On a CPU
>>>supporting LPAE, both TTBR0 accessors are valid. It is the kernel that
>>>chooses to use one rather than the other.
>>
>> Thanks for your review. I don't think both TTBR0 accessors(64bit
>> accessor and 32bit accessor) are valid on a CPU supporting LPAE which
>> the LPAE is enabled. Here is the description come form
>> DDI0406C2c_arm_architecture_reference_manual.pdf (=ARMÂ Architecture
>> Reference Manual ARMv7-A and ARMv7-R edition) which you can get the
>> document by google "ARMÂ Architecture Reference Manual ARMv7-A and
>> ARMv7-R edition".

>Trust me, from where I seat, I have a much better source than Google for
>that document. Who would have thought?

>Nothing in what you randomly quote invalids what I've been saying. And
>to show you what's wrong with your reasoning, let me describe a
>scenario,

>I have a non-LPAE kernel that runs on my system. It uses the 32bit
>version of the TTBRs. It turns out that this kernel runs under a
>hypervisor (KVM, Xen, or your toy of the day). The hypervisor
>context-switches vcpus without even looking at whether the configuration
>of that guest. It doesn't have to care. It just blindly uses the 64bit
>version of the TTBRs.

>The architecture *guarantees* that it works (it even works with a 32bit
>guest under a 64bit hypervisor). In your world, this doesn't work. I
>guess the architecture wins.

>> So, I think if you access TTBR0/TTBR1 on CPU supporting LPAE, you must
>> use "mcrr/mrrc" instruction (__ACCESS_CP15_64). If you access
>> TTBR0/TTBR1 on CPU supporting LPAE by "mcr/mrc" instruction which is
>> 32bit version (__ACCESS_CP15), even if the CPU doesn't report error,
>> you also lose the high or low 32bit of the TTBR0/TTBR1.

>It is not about "supporting LPAE". It is about using the accessor that
>makes sense in a particular context. Yes, the architecture allows you to
>do something stupid. Don't do it. It doesn't mean the accessors cannot
>be used, and I hope that my example above demonstrates it.

>Conclusion: I still stand by my request that both versions of TTBRs/PAR
>are described without depending on the kernel configuration, because
>this has nothing to do with the kernel configuration.

Thanks for your reviews.
Yes, you are right. I have tested that "mcrr/mrrc" instruction (__ACCESS_CP15_64)
can work on non LPAE on vexpress_a9.

Here is the code I tested on vexpress_a9 and vexpress_a15:
--- a/arch/arm/include/asm/cp15.h
+++ b/arch/arm/include/asm/cp15.h
@@ -64,6 +64,56 @@
#define __write_sysreg(v, r, w, c, t) asm volatile(w " " c : : "r" ((t)(v)))
#define write_sysreg(v, ...) __write_sysreg(v, __VA_ARGS__)

+#define TTBR0 __ACCESS_CP15_64(0, c2)
+#define TTBR1 __ACCESS_CP15_64(1, c2)
+#define PAR __ACCESS_CP15_64(0, c7)
+#define VTTBR __ACCESS_CP15_64(6, c2)
+#define CNTV_CVAL __ACCESS_CP15_64(3, c14)
+#define CNTVOFF __ACCESS_CP15_64(4, c14)
+
+#define MIDR __ACCESS_CP15(c0, 0, c0, 0)
+#define CSSELR __ACCESS_CP15(c0, 2, c0, 0)
+#define VPIDR __ACCESS_CP15(c0, 4, c0, 0)
+#define VMPIDR __ACCESS_CP15(c0, 4, c0, 5)
+#define SCTLR __ACCESS_CP15(c1, 0, c0, 0)
+#define CPACR __ACCESS_CP15(c1, 0, c0, 2)
+#define HCR __ACCESS_CP15(c1, 4, c1, 0)
+#define HDCR __ACCESS_CP15(c1, 4, c1, 1)
+#define HCPTR __ACCESS_CP15(c1, 4, c1, 2)
+#define HSTR __ACCESS_CP15(c1, 4, c1, 3)
+#define TTBCR __ACCESS_CP15(c2, 0, c0, 2)
+#define HTCR __ACCESS_CP15(c2, 4, c0, 2)
+#define VTCR __ACCESS_CP15(c2, 4, c1, 2)
+#define DACR __ACCESS_CP15(c3, 0, c0, 0)
+#define DFSR __ACCESS_CP15(c5, 0, c0, 0)
+#define IFSR __ACCESS_CP15(c5, 0, c0, 1)
+#define ADFSR __ACCESS_CP15(c5, 0, c1, 0)
+#define AIFSR __ACCESS_CP15(c5, 0, c1, 1)
+#define HSR __ACCESS_CP15(c5, 4, c2, 0)
+#define DFAR __ACCESS_CP15(c6, 0, c0, 0)
+#define IFAR __ACCESS_CP15(c6, 0, c0, 2)
+#define HDFAR __ACCESS_CP15(c6, 4, c0, 0)
+#define HIFAR __ACCESS_CP15(c6, 4, c0, 2)
+#define HPFAR __ACCESS_CP15(c6, 4, c0, 4)
+#define ICIALLUIS __ACCESS_CP15(c7, 0, c1, 0)
+#define ATS1CPR __ACCESS_CP15(c7, 0, c8, 0)
+#define TLBIALLIS __ACCESS_CP15(c8, 0, c3, 0)
+#define TLBIALL __ACCESS_CP15(c8, 0, c7, 0)
+#define TLBIALLNSNHIS __ACCESS_CP15(c8, 4, c3, 4)
+#define PRRR __ACCESS_CP15(c10, 0, c2, 0)
+#define NMRR __ACCESS_CP15(c10, 0, c2, 1)
+#define AMAIR0 __ACCESS_CP15(c10, 0, c3, 0)
+#define AMAIR1 __ACCESS_CP15(c10, 0, c3, 1)
+#define VBAR __ACCESS_CP15(c12, 0, c0, 0)
+#define CID __ACCESS_CP15(c13, 0, c0, 1)
+#define TID_URW __ACCESS_CP15(c13, 0, c0, 2)
+#define TID_URO __ACCESS_CP15(c13, 0, c0, 3)
+#define TID_PRIV __ACCESS_CP15(c13, 0, c0, 4)
+#define HTPIDR __ACCESS_CP15(c13, 4, c0, 2)
+#define CNTKCTL __ACCESS_CP15(c14, 0, c1, 0)
+#define CNTV_CTL __ACCESS_CP15(c14, 0, c3, 1)
+#define CNTHCTL __ACCESS_CP15(c14, 4, c1, 0)
+
extern unsigned long cr_alignment; /* defined in entry-armv.S */

static inline unsigned long get_cr(void)
diff --git a/arch/arm/include/asm/kvm_hyp.h b/arch/arm/include/asm/kvm_hyp.h
index 14b5903..8db8a8c 100644
--- a/arch/arm/include/asm/kvm_hyp.h
+++ b/arch/arm/include/asm/kvm_hyp.h
@@ -37,56 +37,6 @@
__val; \
})

-#define TTBR0 __ACCESS_CP15_64(0, c2)
-#define TTBR1 __ACCESS_CP15_64(1, c2)
-#define VTTBR __ACCESS_CP15_64(6, c2)
-#define PAR __ACCESS_CP15_64(0, c7)
-#define CNTV_CVAL __ACCESS_CP15_64(3, c14)
-#define CNTVOFF __ACCESS_CP15_64(4, c14)
-
-#define MIDR __ACCESS_CP15(c0, 0, c0, 0)
-#define CSSELR __ACCESS_CP15(c0, 2, c0, 0)
-#define VPIDR __ACCESS_CP15(c0, 4, c0, 0)
-#define VMPIDR __ACCESS_CP15(c0, 4, c0, 5)
-#define SCTLR __ACCESS_CP15(c1, 0, c0, 0)
-#define CPACR __ACCESS_CP15(c1, 0, c0, 2)
-#define HCR __ACCESS_CP15(c1, 4, c1, 0)
-#define HDCR __ACCESS_CP15(c1, 4, c1, 1)
-#define HCPTR __ACCESS_CP15(c1, 4, c1, 2)
-#define HSTR __ACCESS_CP15(c1, 4, c1, 3)
-#define TTBCR __ACCESS_CP15(c2, 0, c0, 2)
-#define HTCR __ACCESS_CP15(c2, 4, c0, 2)
-#define VTCR __ACCESS_CP15(c2, 4, c1, 2)
-#define DACR __ACCESS_CP15(c3, 0, c0, 0)
-#define DFSR __ACCESS_CP15(c5, 0, c0, 0)
-#define IFSR __ACCESS_CP15(c5, 0, c0, 1)
-#define ADFSR __ACCESS_CP15(c5, 0, c1, 0)
-#define AIFSR __ACCESS_CP15(c5, 0, c1, 1)
-#define HSR __ACCESS_CP15(c5, 4, c2, 0)
-#define DFAR __ACCESS_CP15(c6, 0, c0, 0)
-#define IFAR __ACCESS_CP15(c6, 0, c0, 2)
-#define HDFAR __ACCESS_CP15(c6, 4, c0, 0)
-#define HIFAR __ACCESS_CP15(c6, 4, c0, 2)
-#define HPFAR __ACCESS_CP15(c6, 4, c0, 4)
-#define ICIALLUIS __ACCESS_CP15(c7, 0, c1, 0)
-#define ATS1CPR __ACCESS_CP15(c7, 0, c8, 0)
-#define TLBIALLIS __ACCESS_CP15(c8, 0, c3, 0)
-#define TLBIALL __ACCESS_CP15(c8, 0, c7, 0)
-#define TLBIALLNSNHIS __ACCESS_CP15(c8, 4, c3, 4)
-#define PRRR __ACCESS_CP15(c10, 0, c2, 0)
-#define NMRR __ACCESS_CP15(c10, 0, c2, 1)
-#define AMAIR0 __ACCESS_CP15(c10, 0, c3, 0)
-#define AMAIR1 __ACCESS_CP15(c10, 0, c3, 1)
-#define VBAR __ACCESS_CP15(c12, 0, c0, 0)
-#define CID __ACCESS_CP15(c13, 0, c0, 1)
-#define TID_URW __ACCESS_CP15(c13, 0, c0, 2)
-#define TID_URO __ACCESS_CP15(c13, 0, c0, 3)
-#define TID_PRIV __ACCESS_CP15(c13, 0, c0, 4)
-#define HTPIDR __ACCESS_CP15(c13, 4, c0, 2)
-#define CNTKCTL __ACCESS_CP15(c14, 0, c1, 0)
-#define CNTV_CTL __ACCESS_CP15(c14, 0, c3, 1)
-#define CNTHCTL __ACCESS_CP15(c14, 4, c1, 0)
-