[PATCH] powerpc/bpf: Use bctrl for making function calls

[Naveen N. Rao]

Christophe Leroy wrote:
> 
> 
> Le 09/06/2021 à 11:00, Naveen N. Rao a écrit :
>> blrl corrupts the link stack. Instead use bctrl when making function
>> calls from BPF programs.
> 
> What's the link stack ? Is it the PPC64 branch predictor stack ?

c974809a26a13e ("powerpc/vdso: Avoid link stack corruption in 
__get_datapage()") has a good write up on the link stack.

> 
>> 
>> Reported-by: Anton Blanchard <anton at ozlabs.org>
>> Signed-off-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
>> ---
>>   arch/powerpc/include/asm/ppc-opcode.h |  1 +
>>   arch/powerpc/net/bpf_jit_comp32.c     |  4 ++--
>>   arch/powerpc/net/bpf_jit_comp64.c     | 12 ++++++------
>>   3 files changed, 9 insertions(+), 8 deletions(-)
>> 
>> diff --git a/arch/powerpc/include/asm/ppc-opcode.h b/arch/powerpc/include/asm/ppc-opcode.h
>> index ac41776661e963..1abacb8417d562 100644
>> --- a/arch/powerpc/include/asm/ppc-opcode.h
>> +++ b/arch/powerpc/include/asm/ppc-opcode.h
>> @@ -451,6 +451,7 @@
>>   #define PPC_RAW_MTLR(r)			(0x7c0803a6 | ___PPC_RT(r))
>>   #define PPC_RAW_MFLR(t)			(PPC_INST_MFLR | ___PPC_RT(t))
>>   #define PPC_RAW_BCTR()			(PPC_INST_BCTR)
>> +#define PPC_RAW_BCTRL()			(PPC_INST_BCTRL)
> 
> Can you use the numeric value instead of the PPC_INST_BCTRL, to avoid conflict with 
> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/4ca2bfdca2f47a293d05f61eb3c4e487ee170f1f.1621506159.git.christophe.leroy@csgroup.eu/

Sure. I'll post a v2.

- Naveen