Messages in this thread | | | Subject | Re: [PATCH 3/4] bpf powerpc: Add BPF_PROBE_MEM support for 64bit JIT | From | Christophe Leroy <> | Date | Tue, 6 Jul 2021 11:53:43 +0200 |
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Le 06/07/2021 à 09:32, Ravi Bangoria a écrit : > BPF load instruction with BPF_PROBE_MEM mode can cause a fault > inside kernel. Append exception table for such instructions > within BPF program.
Can you do the same for 32bit ?
> > Unlike other archs which uses extable 'fixup' field to pass dest_reg > and nip, BPF exception table on PowerPC follows the generic PowerPC > exception table design, where it populates both fixup and extable > sections witin BPF program. fixup section contains two instructions, > first instruction clears dest_reg and 2nd jumps to next instruction > in the BPF code. extable 'insn' field contains relative offset of > the instruction and 'fixup' field contains relative offset of the > fixup entry. Example layout of BPF program with extable present: > > +------------------+ > | | > | | > 0x4020 -->| ld r27,4(r3) | > | | > | | > 0x40ac -->| lwz r3,0(r4) | > | | > | | > |------------------| > 0x4280 -->| xor r27,r27,r27 | \ fixup entry > | b 0x4024 | / > 0x4288 -->| xor r3,r3,r3 | > | b 0x40b0 | > |------------------| > 0x4290 -->| insn=0xfffffd90 | \ extable entry > | fixup=0xffffffec | / > 0x4298 -->| insn=0xfffffe14 | > | fixup=0xffffffec | > +------------------+ > > (Addresses shown here are chosen random, not real) > > Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com> > --- > arch/powerpc/net/bpf_jit.h | 5 ++- > arch/powerpc/net/bpf_jit_comp.c | 25 +++++++++---- > arch/powerpc/net/bpf_jit_comp32.c | 2 +- > arch/powerpc/net/bpf_jit_comp64.c | 60 ++++++++++++++++++++++++++++++- > 4 files changed, 83 insertions(+), 9 deletions(-) > > diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h > index 411c63d945c7..e9408ad190d3 100644 > --- a/arch/powerpc/net/bpf_jit.h > +++ b/arch/powerpc/net/bpf_jit.h > @@ -141,8 +141,11 @@ struct codegen_context { > unsigned int idx; > unsigned int stack_size; > int b2p[ARRAY_SIZE(b2p)]; > + unsigned int exentry_idx; > }; > > +#define BPF_FIXUP_LEN 8 /* Two instructions */ > + > static inline void bpf_flush_icache(void *start, void *end) > { > smp_wmb(); /* smp write barrier */ > @@ -166,7 +169,7 @@ static inline void bpf_clear_seen_register(struct codegen_context *ctx, int i) > > void bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 func); > int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *ctx, > - u32 *addrs); > + u32 *addrs, int pass); > void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx); > void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx); > void bpf_jit_realloc_regs(struct codegen_context *ctx); > diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c > index a9585e52a88d..3ebd8897cf09 100644 > --- a/arch/powerpc/net/bpf_jit_comp.c > +++ b/arch/powerpc/net/bpf_jit_comp.c > @@ -89,6 +89,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) > { > u32 proglen; > u32 alloclen; > + u32 extable_len = 0; > + u32 fixup_len = 0;
Setting those to 0 doesn't seem to be needed, as it doesn't seem to exist any path to skip the setting below. You should not perform unnecessary init at declaration as it is error prone.
> u8 *image = NULL; > u32 *code_base; > u32 *addrs; > @@ -131,7 +133,6 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) > 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; > } > @@ -149,7 +150,7 @@ 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, 0)) { > /* We hit something illegal or unsupported. */ > fp = org_fp; > goto out_addrs; > @@ -162,7 +163,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) > */ > if (cgctx.seen & SEEN_TAILCALL) { > cgctx.idx = 0; > - if (bpf_jit_build_body(fp, 0, &cgctx, addrs)) { > + if (bpf_jit_build_body(fp, 0, &cgctx, addrs, 0)) { > fp = org_fp; > goto out_addrs; > } > @@ -177,8 +178,11 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) > bpf_jit_build_prologue(0, &cgctx); > bpf_jit_build_epilogue(0, &cgctx); > > + fixup_len = fp->aux->num_exentries * BPF_FIXUP_LEN; > + extable_len = fp->aux->num_exentries * sizeof(struct exception_table_entry); > + > proglen = cgctx.idx * 4; > - alloclen = proglen + FUNCTION_DESCR_SIZE; > + alloclen = proglen + FUNCTION_DESCR_SIZE + fixup_len + extable_len; > > bpf_hdr = bpf_jit_binary_alloc(alloclen, &image, 4, bpf_jit_fill_ill_insns); > if (!bpf_hdr) { > @@ -186,6 +190,11 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) > goto out_addrs; > } > > + if (extable_len) { > + fp->aux->extable = (void *)image + FUNCTION_DESCR_SIZE + > + proglen + fixup_len; > + } > + > skip_init_ctx: > code_base = (u32 *)(image + FUNCTION_DESCR_SIZE); > > @@ -210,7 +219,11 @@ 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); > + if (bpf_jit_build_body(fp, code_base, &cgctx, addrs, pass)) { > + bpf_jit_binary_free(bpf_hdr); > + fp = org_fp; > + goto out_addrs; > + } > bpf_jit_build_epilogue(code_base, &cgctx); > > if (bpf_jit_enable > 1) > @@ -234,7 +247,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) > > fp->bpf_func = (void *)image; > fp->jited = 1; > - fp->jited_len = alloclen; > + fp->jited_len = proglen + FUNCTION_DESCR_SIZE; > > bpf_flush_icache(bpf_hdr, (u8 *)bpf_hdr + (bpf_hdr->pages * PAGE_SIZE)); > if (!fp->is_func || extra_pass) {
This hunk does not apply on latest powerpc tree. You are missing commit 62e3d4210ac9c
> diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c > index 1f81bea35aab..23ab5620a45a 100644 > --- a/arch/powerpc/net/bpf_jit_comp32.c > +++ b/arch/powerpc/net/bpf_jit_comp32.c > @@ -266,7 +266,7 @@ static void bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 > > /* Assemble the body code between the prologue & epilogue */ > int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *ctx, > - u32 *addrs) > + u32 *addrs, int pass) > { > const struct bpf_insn *insn = fp->insnsi; > int flen = fp->len; > diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c > index 984177d9d394..1884c6dca89a 100644 > --- a/arch/powerpc/net/bpf_jit_comp64.c > +++ b/arch/powerpc/net/bpf_jit_comp64.c > @@ -270,9 +270,51 @@ static void bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 > /* out: */ > } > > +static int add_extable_entry(struct bpf_prog *fp, u32 *image, int pass, > + u32 code, struct codegen_context *ctx, int dst_reg) > +{ > + off_t offset; > + unsigned long pc; > + struct exception_table_entry *ex; > + u32 *fixup; > + > + /* Populate extable entries only in the last pass */ > + if (pass != 2 || BPF_MODE(code) != BPF_PROBE_MEM)
'code' is only used for that test, can you do the test before calling add_extable_entry() ?
> + return 0; > + > + if (!fp->aux->extable || > + WARN_ON_ONCE(ctx->exentry_idx >= fp->aux->num_exentries)) > + return -EINVAL; > + > + pc = (unsigned long)&image[ctx->idx - 1];
You should call this function before incrementing ctx->idx
> + > + fixup = (void *)fp->aux->extable - > + (fp->aux->num_exentries * BPF_FIXUP_LEN) + > + (ctx->exentry_idx * BPF_FIXUP_LEN); > + > + fixup[0] = PPC_RAW_XOR(dst_reg, dst_reg, dst_reg);
Prefered way to clear a reg in according to ISA is to do 'li reg, 0'
> + fixup[1] = (PPC_INST_BRANCH | > + (((long)(pc + 4) - (long)&fixup[1]) & 0x03fffffc));
Would be nice if we could have a PPC_RAW_BRANCH() stuff, we could do something like PPC_RAW_BRANCH((long)(pc + 4) - (long)&fixup[1])
> + > + ex = &fp->aux->extable[ctx->exentry_idx]; > + > + offset = pc - (long)&ex->insn; > + if (WARN_ON_ONCE(offset >= 0 || offset < INT_MIN)) > + return -ERANGE; > + ex->insn = offset; > + > + offset = (long)fixup - (long)&ex->fixup; > + if (WARN_ON_ONCE(offset >= 0 || offset < INT_MIN)) > + return -ERANGE; > + ex->fixup = offset; > + > + ctx->exentry_idx++; > + return 0; > +} > + > /* Assemble the body code between the prologue & epilogue */ > int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *ctx, > - u32 *addrs) > + u32 *addrs, int pass) > { > const struct bpf_insn *insn = fp->insnsi; > int flen = fp->len; > @@ -710,25 +752,41 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context * > */ > /* dst = *(u8 *)(ul) (src + off) */ > case BPF_LDX | BPF_MEM | BPF_B: > + case BPF_LDX | BPF_PROBE_MEM | BPF_B:
Could do: + case BPF_LDX | BPF_PROBE_MEM | BPF_B: + ret = add_extable_entry(fp, image, pass, code, ctx, dst_reg); + if (ret) + return ret; case BPF_LDX | BPF_MEM | BPF_B:
> EMIT(PPC_RAW_LBZ(dst_reg, src_reg, off)); > if (insn_is_zext(&insn[i + 1])) > addrs[++i] = ctx->idx * 4; > + ret = add_extable_entry(fp, image, pass, code, ctx, dst_reg); > + if (ret) > + return ret; > break; > /* dst = *(u16 *)(ul) (src + off) */ > case BPF_LDX | BPF_MEM | BPF_H: > + case BPF_LDX | BPF_PROBE_MEM | BPF_H: > EMIT(PPC_RAW_LHZ(dst_reg, src_reg, off)); > if (insn_is_zext(&insn[i + 1])) > addrs[++i] = ctx->idx * 4; > + ret = add_extable_entry(fp, image, pass, code, ctx, dst_reg); > + if (ret) > + return ret; > break; > /* dst = *(u32 *)(ul) (src + off) */ > case BPF_LDX | BPF_MEM | BPF_W: > + case BPF_LDX | BPF_PROBE_MEM | BPF_W: > EMIT(PPC_RAW_LWZ(dst_reg, src_reg, off)); > if (insn_is_zext(&insn[i + 1])) > addrs[++i] = ctx->idx * 4; > + ret = add_extable_entry(fp, image, pass, code, ctx, dst_reg); > + if (ret) > + return ret; > break; > /* dst = *(u64 *)(ul) (src + off) */ > case BPF_LDX | BPF_MEM | BPF_DW: > + case BPF_LDX | BPF_PROBE_MEM | BPF_DW: > PPC_BPF_LL(dst_reg, src_reg, off); > + ret = add_extable_entry(fp, image, pass, code, ctx, dst_reg); > + if (ret) > + return ret; > break; > > /* >
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