[RESEND PATCH v4 0/8] bpf powerpc: Add BPF_PROBE_MEM support in powerpc JIT compiler

[Christophe Leroy]

Le 14/10/2021 à 10:15, David Laight a écrit :
> From: Hari Bathini
>> Sent: 12 October 2021 13:31
>>
>> Patch #1 & #2 are simple cleanup patches. Patch #3 refactors JIT
>> compiler code with the aim to simplify adding BPF_PROBE_MEM support.
>> Patch #4 introduces PPC_RAW_BRANCH() macro instead of open coding
>> branch instruction. Patch #5 & #7 add BPF_PROBE_MEM support for PPC64
>> & PPC32 JIT compilers respectively. Patch #6 & #8 handle bad userspace
>> pointers for PPC64 & PPC32 cases respectively.
> 
> I thought that BPF was only allowed to do fairly restricted
> memory accesses - so WTF does it need a BPF_PROBE_MEM instruction?
> 


Looks like it's been added by commit 2a02759ef5f8 ("bpf: Add support for 
BTF pointers to interpreter")

They say in the log:

     Pointer to BTF object is a pointer to kernel object or NULL.
     The memory access in the interpreter has to be done via 
probe_kernel_read
     to avoid page faults.