Re: [kvm-unit-tests PATCH v2 1/8] s390x: uv-host: Add access checks for donated memory

Steffen Eiden
2022-07-07T08:12:08Z

Hi Janosch,

On 7/6/22 08:40, Janosch Frank wrote:
> Let's check if the UV really protected all the memory we donated.
>
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> ---
> s390x/uv-host.c | 29 +++++++++++++++++++++++++++++
> 1 file changed, 29 insertions(+)
>
> diff --git a/s390x/uv-host.c b/s390x/uv-host.c
> index a1a6d120..983cb4a1 100644
> --- a/s390x/uv-host.c
> +++ b/s390x/uv-host.c
> @@ -43,6 +43,24 @@ static void cpu_loop(void)
> for (;;) {}
> }
>
> +/*
> + * Checks if a memory area is protected as secure memory.
> + * Will return true if all pages are protected, false otherwise.
> + */
> +static bool access_check_3d(uint64_t *access_ptr, uint64_t len)
> +{
> + while (len) {
> + expect_pgm_int();
> + *access_ptr += 42;
> + if (clear_pgm_int() != PGM_INT_CODE_SECURE_STOR_ACCESS)
> + return false;
> + access_ptr += PAGE_SIZE / sizeof(access_ptr);
> + len -= PAGE_SIZE;
If someone uses this function with 'len' not being a multiple of
PAGE_SIZE this test does not for what is was intended by testing more
memory than expected.

I suggest adding an explicit assert at the beginning of the function
that ensures 'len' is a multiple of PAGE_SIZE.

> + }
> +
> + return true;
> +}
> +

[snip]

Steffen