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Message-ID: <0fa8e972-0cd4-ec15-33a9-b3f822e1d67f@csgroup.eu>
Date: Tue, 21 Sep 2021 16:18:14 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Hari Bathini <hbathini@...ux.ibm.com>, naveen.n.rao@...ux.ibm.com,
mpe@...erman.id.au, ast@...nel.org, daniel@...earbox.net
Cc: paulus@...ba.org, andrii@...nel.org, kafai@...com,
songliubraving@...com, yhs@...com, john.fastabend@...il.com,
kpsingh@...nel.org, netdev@...r.kernel.org, bpf@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org,
Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: Re: [PATCH v3 5/8] bpf ppc64: Add BPF_PROBE_MEM support for JIT
Le 21/09/2021 à 15:29, Hari Bathini a écrit :
> From: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
>
> BPF load instruction with BPF_PROBE_MEM mode can cause a fault
> inside kernel. Append exception table for such instructions
> within BPF program.
>
> 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 within 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 -->| li r27,0 | \ fixup entry
> | b 0x4024 | /
> 0x4288 -->| li r3,0 |
> | 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@...ux.ibm.com>
> Signed-off-by: Hari Bathini <hbathini@...ux.ibm.com>
> ---
>
> Changes in v3:
> * Made all changes for bpf_add_extable_entry() in this patch instead
> of updating it again in patch #7.
> * Fixed a coding style issue.
>
>
> arch/powerpc/net/bpf_jit.h | 8 +++-
> arch/powerpc/net/bpf_jit_comp.c | 70 ++++++++++++++++++++++++++++---
> arch/powerpc/net/bpf_jit_comp32.c | 2 +-
> arch/powerpc/net/bpf_jit_comp64.c | 17 +++++++-
> 4 files changed, 88 insertions(+), 9 deletions(-)
>
> diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
> index 0c8f885b8f48..561689a2abdf 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 2 /* Two instructions => 8 bytes */
> +
> static inline void bpf_flush_icache(void *start, void *end)
> {
> smp_wmb(); /* smp write barrier */
> @@ -166,11 +169,14 @@ 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);
>
> +int bpf_add_extable_entry(struct bpf_prog *fp, u32 *image, int pass, struct codegen_context *ctx,
> + int insn_idx, int jmp_off, int dst_reg);
> +
> #endif
>
> #endif
> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index c5c9e8ad1de7..f02457c6b54f 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -101,6 +101,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
> struct bpf_prog *tmp_fp;
> bool bpf_blinded = false;
> bool extra_pass = false;
> + u32 extable_len;
> + u32 fixup_len;
>
> if (!fp->jit_requested)
> return org_fp;
> @@ -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 * 4;
> + 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 +190,9 @@ 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 +217,11 @@ 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 +245,7 @@ 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));
> bpf_jit_binary_lock_ro(bpf_hdr);
> @@ -258,3 +269,50 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
>
> return fp;
> }
> +
> +/*
> + * The caller should check for (BPF_MODE(code) == BPF_PROBE_MEM) before calling
> + * this function, as this only applies to BPF_PROBE_MEM, for now.
> + */
> +int bpf_add_extable_entry(struct bpf_prog *fp, u32 *image, int pass, struct codegen_context *ctx,
> + int insn_idx, int jmp_off, 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)
> + return 0;
> +
> + if (!fp->aux->extable ||
> + WARN_ON_ONCE(ctx->exentry_idx >= fp->aux->num_exentries))
> + return -EINVAL;
> +
> + pc = (unsigned long)&image[insn_idx];
> +
> + fixup = (void *)fp->aux->extable -
> + (fp->aux->num_exentries * BPF_FIXUP_LEN * 4) +
> + (ctx->exentry_idx * BPF_FIXUP_LEN * 4);
> +
> + fixup[0] = PPC_RAW_LI(dst_reg, 0);
> +
> + fixup[BPF_FIXUP_LEN - 1] =
> + PPC_RAW_BRANCH((long)(pc + jmp_off) - (long)&fixup[BPF_FIXUP_LEN - 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;
> +}
> diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c
> index 6e4956cd52e7..820c7848434e 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 991eb43d4cd2..506934c13ef7 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -272,7 +272,7 @@ 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;
> @@ -718,14 +718,22 @@ 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:
> fallthrough;
> + case BPF_LDX | BPF_PROBE_MEM | BPF_B:
> + fallthrough;
fallthrough not needed (see my comment to patch 4)
> /* dst = *(u16 *)(ul) (src + off) */
> case BPF_LDX | BPF_MEM | BPF_H:
> fallthrough;
> + case BPF_LDX | BPF_PROBE_MEM | BPF_H:
> + fallthrough;
> /* dst = *(u32 *)(ul) (src + off) */
> case BPF_LDX | BPF_MEM | BPF_W:
> fallthrough;
> + case BPF_LDX | BPF_PROBE_MEM | BPF_W:
> + fallthrough;
> /* dst = *(u64 *)(ul) (src + off) */
> case BPF_LDX | BPF_MEM | BPF_DW:
> + fallthrough;
> + case BPF_LDX | BPF_PROBE_MEM | BPF_DW:
> switch (size) {
> case BPF_B:
> EMIT(PPC_RAW_LBZ(dst_reg, src_reg, off));
> @@ -749,6 +757,13 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
>
> if (size != BPF_DW && insn_is_zext(&insn[i + 1]))
> addrs[++i] = ctx->idx * 4;
> +
> + if (BPF_MODE(code) == BPF_PROBE_MEM) {
> + ret = bpf_add_extable_entry(fp, image, pass, ctx, ctx->idx - 1,
> + 4, dst_reg);
> + if (ret)
> + return ret;
> + }
> break;
>
> /*
>
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