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Message-ID: <c3b23da2-0781-a1ee-0d49-71e9efb52e66@iogearbox.net>
Date: Fri, 18 May 2018 17:30:35 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Sandipan Das <sandipan@...ux.vnet.ibm.com>, ast@...nel.org
Cc: netdev@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
naveen.n.rao@...ux.vnet.ibm.com, mpe@...erman.id.au,
jakub.kicinski@...ronome.com
Subject: Re: [PATCH bpf v2 2/6] bpf: powerpc64: add JIT support for
multi-function programs
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)?
> + 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().
> + } else {
> + jit_data->addrs = addrs;
> + jit_data->ctx = cgctx;
> + jit_data->proglen = proglen;
> + jit_data->image = image;
> + jit_data->header = bpf_hdr;
> + }
> +
> fp->bpf_func = (void *)image;
> fp->jited = 1;
> fp->jited_len = alloclen;
>
> - bpf_flush_icache(bpf_hdr, (u8 *)bpf_hdr + (bpf_hdr->pages * PAGE_SIZE));
> + if (!fp->is_func || extra_pass) {
> +out_addrs:
> + kfree(addrs);
> + kfree(jit_data);
> + fp->aux->jit_data = NULL;
> + }
>
> out:
> - kfree(addrs);
> -
> if (bpf_blinded)
> bpf_jit_prog_release_other(fp, fp == org_fp ? tmp_fp : org_fp);
>
>
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