On Wed, Mar 20, 2024 at 11:08:00PM -0700, Alexei Starovoitov wrote: > On Wed, Mar 20, 2024 at 3:55 AM Puranjay Mohan <puranjay12@xxxxxxxxx> wrote: > > > > The JITs need to implement bpf_arch_uaddress_limit() to define where > > the userspace addresses end for that architecture or TASK_SIZE is taken > > as default. > > > > The implementation is as follows: > > > > REG_AX = SRC_REG > > if(offset) > > REG_AX += offset; > > REG_AX >>= 32; > > if (REG_AX <= (uaddress_limit >> 32)) > > DST_REG = 0; > > else > > DST_REG = *(size *)(SRC_REG + offset); > > The patch looks good, but it seems to be causing s390 CI failures. > > Ilya, > could you help us understand is this check needed on s390 > and if so, what should be the uaddress_limit ? s390x does not define ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE. Userspace and kernel run in completely different and isolated address spaces, so it's not possible to determine from a pointer value whether it's a user or a kernel pointer. But the good news is that whatever you deference without using special instruction sequences will refer to the kernel address space. So I wonder if we could somehow disable this check on s390x altogether? And if we are not sure whether it's a valid pointer, use BPF_PROBE_MEM as always.
