[RFC,bpf-next,4/4] riscv, bpf: Add bpf trampoline support for RV64

Commit Message

Pu Lehui Dec. 19, 2022, 1:37 p.m. UTC

From: Pu Lehui <[e-mail]>

BPF trampoline is the critical infrastructure of the bpf
subsystem, acting as a mediator between kernel functions
and BPF programs. Numerous important features, such as
using ebpf program for zero overhead kernel introspection,
rely on this key component. We can't wait to support bpf
trampoline on RV64. The implementation of bpf trampoline
was closely to x86 and arm64 for future development. The
related tests have passed, as well as the test_verifier
with no new failure ceses.

Signed-off-by: Pu Lehui <[e-mail]>
---
 arch/riscv/net/bpf_jit_comp64.c | 323 ++++++++++++++++++++++++++++++++
 1 file changed, 323 insertions(+)

Patch

diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index fa8b03c52463..128059e6d744 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -738,6 +738,329 @@  int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type,
 	       bpf_text_poke_jump(ip, old_addr, new_addr);
 }
 
+static void store_args(int nregs, int args_off, struct rv_jit_context *ctx)
+{
+	int i;
+
+	for (i = 0; i < nregs; i++) {
+		emit_sd(RV_REG_FP, -args_off, RV_REG_A0 + i, ctx);
+		args_off -= 8;
+	}
+}
+
+static void restore_args(int nregs, int args_off, struct rv_jit_context *ctx)
+{
+	int i;
+
+	for (i = 0; i < nregs; i++) {
+		emit_ld(RV_REG_A0 + i, -args_off, RV_REG_FP, ctx);
+		args_off -= 8;
+	}
+}
+
+static int invoke_bpf_prog(struct bpf_tramp_link *l, int args_off, int retval_off,
+			   int run_ctx_off, bool save_ret, struct rv_jit_context *ctx)
+{
+	u32 insn;
+	int ret, branch_off, offset;
+	struct bpf_prog *p = l->link.prog;
+	int cookie_off = offsetof(struct bpf_tramp_run_ctx, bpf_cookie);
+
+	if (l->cookie) {
+		emit_imm(RV_REG_T1, l->cookie, ctx);
+		emit_sd(RV_REG_FP, -run_ctx_off + cookie_off, RV_REG_T1, ctx);
+	} else {
+		emit_sd(RV_REG_FP, -run_ctx_off + cookie_off, RV_REG_ZERO, ctx);
+	}
+
+	/* arg1: prog */
+	emit_imm(RV_REG_A0, (const s64)p, ctx);
+	/* arg2: &run_ctx */
+	emit_addi(RV_REG_A1, RV_REG_FP, -run_ctx_off, ctx);
+	ret = emit_call((const u64)bpf_trampoline_enter(p), true, ctx);
+	if (ret)
+		return ret;
+
+	/* if (__bpf_prog_enter(prog) == 0)
+	 *	goto skip_exec_of_prog;
+	 */
+	branch_off = ctx->ninsns;
+	/* nop reserved for conditional jump */
+	emit(rv_nop(), ctx);
+
+	/* store prog start time */
+	emit_mv(RV_REG_S1, RV_REG_A0, ctx);
+
+	/* arg1: &args_off */
+	emit_addi(RV_REG_A0, RV_REG_FP, -args_off, ctx);
+	if (!p->jited)
+		/* arg2: progs[i]->insnsi for interpreter */
+		emit_imm(RV_REG_A1, (const s64)p->insnsi, ctx);
+	ret = emit_call((const u64)p->bpf_func, true, ctx);
+	if (ret)
+		return ret;
+
+	if (save_ret)
+		emit_sd(RV_REG_FP, -retval_off, regmap[BPF_REG_0], ctx);
+
+	/* update branch with beqz */
+	offset = ninsns_rvoff(ctx->ninsns - branch_off);
+	insn = rv_beq(RV_REG_A0, RV_REG_ZERO, offset >> 1);
+	*(u32 *)(ctx->insns + branch_off) = insn;
+
+	/* arg1: prog */
+	emit_imm(RV_REG_A0, (const s64)p, ctx);
+	/* arg2: prog start time */
+	emit_mv(RV_REG_A1, RV_REG_S1, ctx);
+	/* arg3: &run_ctx */
+	emit_addi(RV_REG_A2, RV_REG_FP, -run_ctx_off, ctx);
+	ret = emit_call((const u64)bpf_trampoline_exit(p), true, ctx);
+
+	return ret;
+}
+
+static int invoke_bpf_mod_ret(struct bpf_tramp_links *tl, int args_off, int retval_off,
+			      int run_ctx_off, int *branches_off, struct rv_jit_context *ctx)
+{
+	int i, ret;
+
+	/* cleanup to avoid garbage return value confusion */
+	emit_sd(RV_REG_FP, -retval_off, RV_REG_ZERO, ctx);
+	for (i = 0; i < tl->nr_links; i++) {
+		ret = invoke_bpf_prog(tl->links[i], args_off, retval_off,
+				run_ctx_off, true, ctx);
+		if (ret)
+			return ret;
+		emit_ld(RV_REG_T1, -retval_off, RV_REG_FP, ctx);
+		branches_off[i] = ctx->ninsns;
+		This nop will be replaced with a cbnz later
+		/* nop reserved for conditional jump */
+		emit(rv_nop(), ctx);
+	}
+
+	return 0;
+}
+
+static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
+					 const struct btf_func_model *m,
+					 struct bpf_tramp_links *tlinks,
+					 void *func_addr, u32 flags,
+					 struct rv_jit_context *ctx)
+{
+	int i, ret, offset;
+	int *branches_off = NULL;
+	int stack_size = 0, nregs = m->nr_args;
+	int retaddr_off, fp_off, retval_off, args_off;
+	int nregs_off, ip_off, run_ctx_off, sreg_off;
+	struct bpf_tramp_links *fentry = &tlinks[BPF_TRAMP_FENTRY];
+	struct bpf_tramp_links *fexit = &tlinks[BPF_TRAMP_FEXIT];
+	struct bpf_tramp_links *fmod_ret = &tlinks[BPF_TRAMP_MODIFY_RETURN];
+	void *orig_call = func_addr;
+	bool save_ret;
+	u32 insn;
+
+	/* Generated trampoline stack layout:
+	 *
+	 * FP - 8	    [ RA of parent func	] return address of parent
+	 *					  function
+	 * FP - retaddr_off [ RA of traced func	] return address of traced
+	 *					  function
+	 * FP - fp_off	    [ FP of parent func ]
+	 *
+	 * FP - retval_off  [ return value      ] BPF_TRAMP_F_CALL_ORIG or
+	 *					  BPF_TRAMP_F_RET_FENTRY_RET
+	 *                  [ argN              ]
+	 *                  [ ...               ]
+	 * FP - args_off    [ arg1              ]
+	 *
+	 * FP - nregs_off   [ regs count        ]
+	 *
+	 * FP - ip_off      [ traced func	] BPF_TRAMP_F_IP_ARG
+	 *
+	 * FP - run_ctx_off [ bpf_tramp_run_ctx ]
+	 *
+	 * FP - sreg_off    [ callee saved reg	]
+	 *
+	 *		    [ pads              ] pads for 16 bytes alignment
+	 */
+
+	if (flags & (BPF_TRAMP_F_ORIG_STACK | BPF_TRAMP_F_SHARE_IPMODIFY))
+		return -ENOTSUPP;
+
+	/* extra regiters for struct arguments */
+	for (i = 0; i < m->nr_args; i++)
+		if (m->arg_flags[i] & BTF_FMODEL_STRUCT_ARG)
+			nregs += round_up(m->arg_size[i], 8) / 8 - 1;
+
+	/* 8 arguments passed by registers */
+	if (nregs > 8)
+		return -ENOTSUPP;
+
+	/* room for parent function return address */
+	stack_size += 8;
+
+	stack_size += 8;
+	retaddr_off = stack_size;
+
+	stack_size += 8;
+	fp_off = stack_size;
+
+	save_ret = flags & (BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_RET_FENTRY_RET);
+	if (save_ret) {
+		stack_size += 8;
+		retval_off = stack_size;
+	}
+
+	stack_size += nregs * 8;
+	args_off = stack_size;
+
+	stack_size += 8;
+	nregs_off = stack_size;
+
+	if (flags & BPF_TRAMP_F_IP_ARG) {
+		stack_size += 8;
+		ip_off = stack_size;
+	}
+
+	stack_size += round_up(sizeof(struct bpf_tramp_run_ctx), 8);
+	run_ctx_off = stack_size;
+
+	stack_size += 8;
+	sreg_off = stack_size;
+
+	stack_size = round_up(stack_size, 16);
+
+	emit_addi(RV_REG_SP, RV_REG_SP, -stack_size, ctx);
+
+	emit_sd(RV_REG_SP, stack_size - retaddr_off, RV_REG_RA, ctx);
+	emit_sd(RV_REG_SP, stack_size - fp_off, RV_REG_FP, ctx);
+
+	emit_addi(RV_REG_FP, RV_REG_SP, stack_size, ctx);
+
+	/* callee saved register S1 to pass start time */
+	emit_sd(RV_REG_FP, -sreg_off, RV_REG_S1, ctx);
+
+	/* store ip address of the traced function */
+	if (flags & BPF_TRAMP_F_IP_ARG) {
+		emit_imm(RV_REG_T1, (const s64)func_addr, ctx);
+		emit_sd(RV_REG_FP, -ip_off, RV_REG_T1, ctx);
+	}
+
+	emit_li(RV_REG_T1, nregs, ctx);
+	emit_sd(RV_REG_FP, -nregs_off, RV_REG_T1, ctx);
+
+	store_args(nregs, args_off, ctx);
+
+	/* skip to actual body of traced function */
+	if (flags & BPF_TRAMP_F_SKIP_FRAME)
+		orig_call += 16;
+
+	if (flags & BPF_TRAMP_F_CALL_ORIG) {
+		emit_imm(RV_REG_A0, (const s64)im, ctx);
+		ret = emit_call((const u64)__bpf_tramp_enter, true, ctx);
+		if (ret)
+			return ret;
+	}
+
+	for (i = 0; i < fentry->nr_links; i++) {
+		ret = invoke_bpf_prog(fentry->links[i], args_off, retval_off, run_ctx_off,
+				      flags & BPF_TRAMP_F_RET_FENTRY_RET, ctx);
+		if (ret)
+			return ret;
+	}
+
+	if (fmod_ret->nr_links) {
+		branches_off = kcalloc(fmod_ret->nr_links, sizeof(int), GFP_KERNEL);
+		if (!branches_off)
+			return -ENOMEM;
+
+		ret = invoke_bpf_mod_ret(fmod_ret, args_off, retval_off, run_ctx_off,
+					 branches_off, ctx);
+		if (ret)
+			return ret;
+	}
+
+	if (flags & BPF_TRAMP_F_CALL_ORIG) {
+		restore_args(nregs, args_off, ctx);
+		ret = emit_call((const u64)orig_call, true, ctx);
+		if (ret)
+			return ret;
+		emit_sd(RV_REG_FP, -retval_off, RV_REG_A0, ctx);
+		/* nop reserved for bpf_tramp_image_put */
+		im->ip_after_call = ctx->insns + ctx->ninsns;
+		emit(rv_nop(), ctx);
+	}
+
+	/* update branches saved in invoke_bpf_mod_ret with bnez */
+	for (i = 0; i < fmod_ret->nr_links; i++) {
+		offset = ninsns_rvoff(ctx->ninsns - branches_off[i]);
+		insn = rv_bne(RV_REG_T1, RV_REG_ZERO, offset >> 1);
+		*(u32 *)(ctx->insns + branches_off[i]) = insn;
+	}
+
+	for (i = 0; i < fexit->nr_links; i++) {
+		ret = invoke_bpf_prog(fexit->links[i], args_off, retval_off,
+				      run_ctx_off, false, ctx);
+		if (ret)
+			return ret;
+	}
+
+	if (flags & BPF_TRAMP_F_CALL_ORIG) {
+		im->ip_epilogue = ctx->insns + ctx->ninsns;
+		emit_imm(RV_REG_A0, (const s64)im, ctx);
+		ret = emit_call((const u64)__bpf_tramp_exit, true, ctx);
+		if (ret)
+			return ret;
+	}
+
+	if (flags & BPF_TRAMP_F_RESTORE_REGS)
+		restore_args(nregs, args_off, ctx);
+
+	if (save_ret)
+		emit_ld(RV_REG_A0, -retval_off, RV_REG_FP, ctx);
+
+	emit_ld(RV_REG_S1, -sreg_off, RV_REG_FP, ctx);
+
+	if (flags & BPF_TRAMP_F_SKIP_FRAME)
+		/* return address of parent function */
+		emit_ld(RV_REG_RA, stack_size - 8, RV_REG_SP, ctx);
+	else
+		/* return address of traced function */
+		emit_ld(RV_REG_RA, stack_size - retaddr_off, RV_REG_SP, ctx);
+
+	emit_ld(RV_REG_FP, stack_size - fp_off, RV_REG_SP, ctx);
+	emit_addi(RV_REG_SP, RV_REG_SP, stack_size, ctx);
+
+	emit_jalr(RV_REG_ZERO, RV_REG_RA, 0, ctx);
+
+	bpf_flush_icache(ctx->insns, ctx->insns + ctx->ninsns);
+
+	kfree(branches_off);
+
+	return ctx->ninsns;
+
+}
+
+int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image,
+				void *image_end, const struct btf_func_model *m,
+				u32 flags, struct bpf_tramp_links *tlinks,
+				void *func_addr)
+{
+	int ret;
+	struct rv_jit_context ctx;
+
+	ctx.ninsns = 0;
+	ctx.insns = image;
+	ret = __arch_prepare_bpf_trampoline(im, m, tlinks, func_addr, flags, &ctx);
+	if (ret < 0)
+		return ret;
+
+	if (ninsns_rvoff(ret) > (long)image_end - (long)image)
+		return -EFBIG;
+
+	return ninsns_rvoff(ret);
+}
+
 int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 		      bool extra_pass)
 {