Re: [kvm-unit-tests PATCH] x86: vmx: Mask undefined bits in exit qualifications

[Krish Sadhukhan <krish.sadhukhan@oracle.com>]

On 06/17/2019 03:46 PM, Nadav Amit wrote:
>> On Jun 17, 2019, at 3:22 PM, Krish Sadhukhan <krish.sadhukhan@oracle.com> wrote:
>>
>>
>>
>> On 06/17/2019 12:52 PM, Nadav Amit wrote:
>>>> On May 3, 2019, at 10:49 AM, nadav.amit@gmail.com wrote:
>>>>
>>>> From: Nadav Amit <nadav.amit@gmail.com>
>>>>
>>>> On EPT violation, the exit qualifications may have some undefined bits.
>>>>
>>>> Bit 6 is undefined if "mode-based execute control" is 0.
>>>>
>>>> Bits 9-11 are undefined unless the processor supports advanced VM-exit
>>>> information for EPT violations.
>>>>
>>>> Right now on KVM these bits are always undefined inside the VM (i.e., in
>>>> an emulated VM-exit). Mask these bits to avoid potential false
>>>> indication of failures.
>>>>
>>>> Signed-off-by: Nadav Amit <nadav.amit@gmail.com>
>>>> ---
>>>> x86/vmx.h       | 20 ++++++++++++--------
>>>> x86/vmx_tests.c |  4 ++++
>>>> 2 files changed, 16 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/x86/vmx.h b/x86/vmx.h
>>>> index cc377ef..5053d6f 100644
>>>> --- a/x86/vmx.h
>>>> +++ b/x86/vmx.h
>>>> @@ -603,16 +603,20 @@ enum vm_instruction_error_number {
>>>> #define EPT_ADDR_MASK		GENMASK_ULL(51, 12)
>>>> #define PAGE_MASK_2M		(~(PAGE_SIZE_2M-1))
>>>>
>>>> -#define EPT_VLT_RD		1
>>>> -#define EPT_VLT_WR		(1 << 1)
>>>> -#define EPT_VLT_FETCH		(1 << 2)
>>>> -#define EPT_VLT_PERM_RD		(1 << 3)
>>>> -#define EPT_VLT_PERM_WR		(1 << 4)
>>>> -#define EPT_VLT_PERM_EX		(1 << 5)
>>>> +#define EPT_VLT_RD		(1ull << 0)
>>>> +#define EPT_VLT_WR		(1ull << 1)
>>>> +#define EPT_VLT_FETCH		(1ull << 2)
>>>> +#define EPT_VLT_PERM_RD		(1ull << 3)
>>>> +#define EPT_VLT_PERM_WR		(1ull << 4)
>>>> +#define EPT_VLT_PERM_EX		(1ull << 5)
>>>> +#define EPT_VLT_PERM_USER_EX	(1ull << 6)
>>>> #define EPT_VLT_PERMS		(EPT_VLT_PERM_RD | EPT_VLT_PERM_WR | \
>>>> 				 EPT_VLT_PERM_EX)
>>>> -#define EPT_VLT_LADDR_VLD	(1 << 7)
>>>> -#define EPT_VLT_PADDR		(1 << 8)
>>>> +#define EPT_VLT_LADDR_VLD	(1ull << 7)
>>>> +#define EPT_VLT_PADDR		(1ull << 8)
>>>> +#define EPT_VLT_GUEST_USER	(1ull << 9)
>>>> +#define EPT_VLT_GUEST_WR	(1ull << 10)
>> This one should be named EPT_VLT_GUEST_RW, assuming you are naming them
>> according to the 1-setting of the bits.
> Whatever you wish (unless someone else has different preference).
>
>>>> +#define EPT_VLT_GUEST_EX	(1ull << 11)
>>>>
>>>> #define MAGIC_VAL_1		0x12345678ul
>>>> #define MAGIC_VAL_2		0x87654321ul
>>>> diff --git a/x86/vmx_tests.c b/x86/vmx_tests.c
>>>> index c52ebc6..b4129e1 100644
>>>> --- a/x86/vmx_tests.c
>>>> +++ b/x86/vmx_tests.c
>>>> @@ -2365,6 +2365,10 @@ static void do_ept_violation(bool leaf, enum ept_access_op op,
>>>>
>>>> 	qual = vmcs_read(EXI_QUALIFICATION);
>>>>
>>>> +	/* Mask undefined bits (which may later be defined in certain cases). */
>>>> +	qual &= ~(EPT_VLT_GUEST_USER | EPT_VLT_GUEST_WR | EPT_VLT_GUEST_EX |
>>>> +		 EPT_VLT_PERM_USER_EX);
>>>> +
>> The "DIAGNOSE" macro doesn't check any of these bits, so this masking
>> seems redundant.
> The DIAGNOSE macro is not the one who causes errors. It’s the:
>
>    TEST_EXPECT_EQ(expected_qual, qual);
>
> That comes right after the call to diagnose_ept_violation_qual().

Sorry, I missed that !

>
>> Also, don't we need to check for the relevant conditions before masking
>> the bits ? For example, EPT_VLT_PERM_USER_EX is dependent on "mode-based
>> execute control" VM-execution control" and the other ones depend on bit 7
>> and 8 of the Exit Qualification field.
> The tests right now do not “emulate” these bits, so the expected
> qualification would never have EPT_VLT_PERM_USER_EX (for instance) set. Once
> someone implements tests for these bits, he would need to change the
> masking.
>

Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>