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Message-Id: <1526658936.9wk22hv49g.naveen@linux.ibm.com>
Date: Fri, 18 May 2018 21:35:14 +0530
From: "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To: ast@...nel.org, Daniel Borkmann <daniel@...earbox.net>,
Sandipan Das <sandipan@...ux.vnet.ibm.com>
Cc: jakub.kicinski@...ronome.com, linuxppc-dev@...ts.ozlabs.org,
mpe@...erman.id.au, netdev@...r.kernel.org
Subject: Re: [PATCH bpf v2 2/6] bpf: powerpc64: add JIT support for
multi-function programs
Daniel Borkmann wrote:
> On 05/18/2018 02:50 PM, Sandipan Das wrote:
>> This adds support for bpf-to-bpf function calls in the powerpc64
>> JIT compiler. The JIT compiler converts the bpf call instructions
>> to native branch instructions. After a round of the usual passes,
>> the start addresses of the JITed images for the callee functions
>> are known. Finally, to fixup the branch target addresses, we need
>> to perform an extra pass.
>>
>> Because of the address range in which JITed images are allocated
>> on powerpc64, the offsets of the start addresses of these images
>> from __bpf_call_base are as large as 64 bits. So, for a function
>> call, we cannot use the imm field of the instruction to determine
>> the callee's address. Instead, we use the alternative method of
>> getting it from the list of function addresses in the auxillary
>> data of the caller by using the off field as an index.
>>
>> Signed-off-by: Sandipan Das <sandipan@...ux.vnet.ibm.com>
>> ---
>> arch/powerpc/net/bpf_jit_comp64.c | 79 ++++++++++++++++++++++++++++++++++-----
>> 1 file changed, 69 insertions(+), 10 deletions(-)
>>
>> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
>> index 1bdb1aff0619..25939892d8f7 100644
>> --- a/arch/powerpc/net/bpf_jit_comp64.c
>> +++ b/arch/powerpc/net/bpf_jit_comp64.c
>> @@ -256,7 +256,7 @@ static void bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32
>> /* Assemble the body code between the prologue & epilogue */
>> static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image,
>> struct codegen_context *ctx,
>> - u32 *addrs)
>> + u32 *addrs, bool extra_pass)
>> {
>> const struct bpf_insn *insn = fp->insnsi;
>> int flen = fp->len;
>> @@ -712,11 +712,23 @@ static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image,
>> break;
>>
>> /*
>> - * Call kernel helper
>> + * Call kernel helper or bpf function
>> */
>> case BPF_JMP | BPF_CALL:
>> ctx->seen |= SEEN_FUNC;
>> - func = (u8 *) __bpf_call_base + imm;
>> +
>> + /* bpf function call */
>> + if (insn[i].src_reg == BPF_PSEUDO_CALL && extra_pass)
>
> Perhaps it might make sense here for !extra_pass to set func to some dummy
> address as otherwise the 'kernel helper call' branch used for this is a bit
> misleading in that sense. The PPC_LI64() used in bpf_jit_emit_func_call()
> optimizes the immediate addr, I presume the JIT can handle situations where
> in the final extra_pass the image needs to grow/shrink again (due to different
> final address for the call)?
That's a good catch. We don't handle that -- we expect to get the size
right on first pass. We could probably have PPC_FUNC_ADDR() pad the
result with nops to make it a constant 5-instruction sequence.
>
>> + if (fp->aux->func && off < fp->aux->func_cnt)
>> + /* use the subprog id from the off
>> + * field to lookup the callee address
>> + */
>> + func = (u8 *) fp->aux->func[off]->bpf_func;
>> + else
>> + return -EINVAL;
>> + /* kernel helper call */
>> + else
>> + func = (u8 *) __bpf_call_base + imm;
>>
>> bpf_jit_emit_func_call(image, ctx, (u64)func);
>>
>> @@ -864,6 +876,14 @@ static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image,
>> return 0;
>> }
>>
>> +struct powerpc64_jit_data {
>> + struct bpf_binary_header *header;
>> + u32 *addrs;
>> + u8 *image;
>> + u32 proglen;
>> + struct codegen_context ctx;
>> +};
>> +
>> struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
>> {
>> u32 proglen;
>> @@ -871,6 +891,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
>> u8 *image = NULL;
>> u32 *code_base;
>> u32 *addrs;
>> + struct powerpc64_jit_data *jit_data;
>> struct codegen_context cgctx;
>> int pass;
>> int flen;
>> @@ -878,6 +899,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
>> struct bpf_prog *org_fp = fp;
>> struct bpf_prog *tmp_fp;
>> bool bpf_blinded = false;
>> + bool extra_pass = false;
>>
>> if (!fp->jit_requested)
>> return org_fp;
>> @@ -891,7 +913,28 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
>> fp = tmp_fp;
>> }
>>
>> + jit_data = fp->aux->jit_data;
>> + if (!jit_data) {
>> + jit_data = kzalloc(sizeof(*jit_data), GFP_KERNEL);
>> + if (!jit_data) {
>> + fp = org_fp;
>> + goto out;
>> + }
>> + fp->aux->jit_data = jit_data;
>> + }
>> +
>> flen = fp->len;
>> + addrs = jit_data->addrs;
>> + if (addrs) {
>> + cgctx = jit_data->ctx;
>> + image = jit_data->image;
>> + bpf_hdr = jit_data->header;
>> + proglen = jit_data->proglen;
>> + alloclen = proglen + FUNCTION_DESCR_SIZE;
>> + extra_pass = true;
>> + goto skip_init_ctx;
>> + }
>> +
>> addrs = kzalloc((flen+1) * sizeof(*addrs), GFP_KERNEL);
>> if (addrs == NULL) {
>> fp = org_fp;
>
> In this case of !addrs, we leak the just allocated jit_data here!
>
>> @@ -904,10 +947,10 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
>> cgctx.stack_size = round_up(fp->aux->stack_depth, 16);
>>
>> /* Scouting faux-generate pass 0 */
>> - if (bpf_jit_build_body(fp, 0, &cgctx, addrs)) {
>> + if (bpf_jit_build_body(fp, 0, &cgctx, addrs, false)) {
>> /* We hit something illegal or unsupported. */
>> fp = org_fp;
>> - goto out;
>> + goto out_addrs;
>> }
>>
>> /*
>> @@ -925,9 +968,10 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
>> bpf_jit_fill_ill_insns);
>> if (!bpf_hdr) {
>> fp = org_fp;
>> - goto out;
>> + goto out_addrs;
>> }
>>
>> +skip_init_ctx:
>> code_base = (u32 *)(image + FUNCTION_DESCR_SIZE);
>>
>> /* Code generation passes 1-2 */
>> @@ -935,7 +979,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
>> /* Now build the prologue, body code & epilogue for real. */
>> cgctx.idx = 0;
>> bpf_jit_build_prologue(code_base, &cgctx);
>> - bpf_jit_build_body(fp, code_base, &cgctx, addrs);
>> + bpf_jit_build_body(fp, code_base, &cgctx, addrs, extra_pass);
>> bpf_jit_build_epilogue(code_base, &cgctx);
>>
>> if (bpf_jit_enable > 1)
>> @@ -956,15 +1000,30 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
>> ((u64 *)image)[1] = local_paca->kernel_toc;
>> #endif
>>
>> + bpf_flush_icache(bpf_hdr, (u8 *)bpf_hdr + (bpf_hdr->pages * PAGE_SIZE));
>> +
>> + if (!fp->is_func || extra_pass) {
>> + bpf_jit_binary_lock_ro(bpf_hdr);
>
> powerpc doesn't implement set_memory_ro(). Generally this is not a problem since
> set_memory_ro() defaults to 'return 0' in this case, but since the bpf_jit_free()
> destructor is overridden here, there's no bpf_jit_binary_unlock_ro() and in case
> powerpc would get set_memory_*() support one day this will then crash in random
> places once the mem gets back to the allocator, thus hard to debug. Two options:
> either you remove the bpf_jit_free() override or you remove the bpf_jit_binary_lock_ro().
Yeah, we shouldn't be using the lock here.
Thanks,
Naveen
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