Re: [PATCH v4 bpf-next] selftests/bpf: Use the last page in test_snprintf_btf on s390

[Heiko Carstens <hca@linux.ibm.com>]

On Sat, Feb 27, 2021 at 06:17:26AM +0100, Ilya Leoshkevich wrote:
> test_snprintf_btf fails on s390, because NULL points to a readable
> struct lowcore there. Fix by using the last page instead.
> 
> Error message example:
> 
>     printing fffffffffffff000 should generate error, got (361)
> 
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
> 
> 
> v1: https://lore.kernel.org/bpf/20210226135923.114211-1-iii@linux.ibm.com/
> v1 -> v2: Yonghong suggested to add the pointer value to the error
>           message.
>           I've noticed that I've been passing BADPTR as flags, therefore
>           the fix worked only by accident. Put it into p.ptr where it
>           belongs.
> 
> v2: https://lore.kernel.org/bpf/20210226182014.115347-1-iii@linux.ibm.com/
> v2 -> v3: Heiko mentioned that using _REGION1_SIZE is not future-proof.
>           We had a private discussion and came to the conclusion that
>           the the last page is good enough.
> 
> v3: https://lore.kernel.org/bpf/20210226190908.115706-1-iii@linux.ibm.com/
> v3 -> v4: Yonghong suggested to print the non-hashed pointer value.
> 
>  .../testing/selftests/bpf/progs/netif_receive_skb.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)

Just in case, also for v4:

Acked-by: Heiko Carstens <hca@linux.ibm.com>