bpf, riscv: Implement PROBE_MEM32 pseudo instructions

Add support for [LDX | STX | ST], PROBE_MEM32, [B | H | W | DW]
instructions. They are similar to PROBE_MEM instructions with the
following differences:

- PROBE_MEM32 supports store.
- PROBE_MEM32 relies on the verifier to clear upper 32-bit of the
  src/dst register
- PROBE_MEM32 adds 64-bit kern_vm_start address (which is stored in S7
  in the prologue). Due to bpf_arena constructions such S7 + reg +
  off16 access is guaranteed to be within arena virtual range, so no
  address check at run-time.
- S11 is a free callee-saved register, so it is used to store kern_vm_start
- PROBE_MEM32 allows STX and ST. If they fault the store is a nop. When
  LDX faults the destination register is zeroed.

To support these on riscv, we do tmp = S7 + src/dst reg and then use
tmp2 as the new src/dst register. This allows us to reuse most of the
code for normal [LDX | STX | ST].
Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Björn Töpel <bjorn@rivosinc.com>
Tested-by: Pu Lehui <pulehui@huawei.com>
Reviewed-by: Pu Lehui <pulehui@huawei.com>
Acked-by: Björn Töpel <bjorn@kernel.org>
Link: https://lore.kernel.org/bpf/20240404114203.105970-2-puranjay12@gmail.com

arch/riscv/net/bpf_jit.h

@@ -81,6 +81,7 @@ struct rv_jit_context {
 	int nexentries;
 	unsigned long flags;
 	int stack_size;
+	u64 arena_vm_start;
 };
 
 /* Convert from ninsns to bytes. */

arch/riscv/net/bpf_jit_comp64.c

@@ -18,6 +18,7 @@
 
 #define RV_REG_TCC RV_REG_A6
 #define RV_REG_TCC_SAVED RV_REG_S6 /* Store A6 in S6 if program do calls */
+#define RV_REG_ARENA RV_REG_S7 /* For storing arena_vm_start */
 
 static const int regmap[] = {
 	[BPF_REG_0] =	RV_REG_A5,
@@ -255,6 +256,10 @@ static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx)
 		emit_ld(RV_REG_S6, store_offset, RV_REG_SP, ctx);
 		store_offset -= 8;
 	}
+	if (ctx->arena_vm_start) {
+		emit_ld(RV_REG_ARENA, store_offset, RV_REG_SP, ctx);
+		store_offset -= 8;
+	}
 
 	emit_addi(RV_REG_SP, RV_REG_SP, stack_adjust, ctx);
 	/* Set return value. */
@@ -548,6 +553,7 @@ static void emit_atomic(u8 rd, u8 rs, s16 off, s32 imm, bool is64,
 
 #define BPF_FIXUP_OFFSET_MASK   GENMASK(26, 0)
 #define BPF_FIXUP_REG_MASK      GENMASK(31, 27)
+#define REG_DONT_CLEAR_MARKER	0	/* RV_REG_ZERO unused in pt_regmap */
 
 bool ex_handler_bpf(const struct exception_table_entry *ex,
 		    struct pt_regs *regs)
@@ -555,7 +561,8 @@ bool ex_handler_bpf(const struct exception_table_entry *ex,
 	off_t offset = FIELD_GET(BPF_FIXUP_OFFSET_MASK, ex->fixup);
 	int regs_offset = FIELD_GET(BPF_FIXUP_REG_MASK, ex->fixup);
 
-	*(unsigned long *)((void *)regs + pt_regmap[regs_offset]) = 0;
+	if (regs_offset != REG_DONT_CLEAR_MARKER)
+		*(unsigned long *)((void *)regs + pt_regmap[regs_offset]) = 0;
 	regs->epc = (unsigned long)&ex->fixup - offset;
 
 	return true;
@@ -572,7 +579,8 @@ static int add_exception_handler(const struct bpf_insn *insn,
 	off_t fixup_offset;
 
 	if (!ctx->insns || !ctx->ro_insns || !ctx->prog->aux->extable ||
-	    (BPF_MODE(insn->code) != BPF_PROBE_MEM && BPF_MODE(insn->code) != BPF_PROBE_MEMSX))
+	    (BPF_MODE(insn->code) != BPF_PROBE_MEM && BPF_MODE(insn->code) != BPF_PROBE_MEMSX &&
+	     BPF_MODE(insn->code) != BPF_PROBE_MEM32))
 		return 0;
 
 	if (WARN_ON_ONCE(ctx->nexentries >= ctx->prog->aux->num_exentries))
@@ -1539,6 +1547,11 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 	case BPF_LDX | BPF_PROBE_MEMSX | BPF_B:
 	case BPF_LDX | BPF_PROBE_MEMSX | BPF_H:
 	case BPF_LDX | BPF_PROBE_MEMSX | BPF_W:
+	/* LDX | PROBE_MEM32: dst = *(unsigned size *)(src + RV_REG_ARENA + off) */
+	case BPF_LDX | BPF_PROBE_MEM32 | BPF_B:
+	case BPF_LDX | BPF_PROBE_MEM32 | BPF_H:
+	case BPF_LDX | BPF_PROBE_MEM32 | BPF_W:
+	case BPF_LDX | BPF_PROBE_MEM32 | BPF_DW:
 	{
 		int insn_len, insns_start;
 		bool sign_ext;
@@ -1546,6 +1559,11 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 		sign_ext = BPF_MODE(insn->code) == BPF_MEMSX ||
 			   BPF_MODE(insn->code) == BPF_PROBE_MEMSX;
 
+		if (BPF_MODE(insn->code) == BPF_PROBE_MEM32) {
+			emit_add(RV_REG_T2, rs, RV_REG_ARENA, ctx);
+			rs = RV_REG_T2;
+		}
+
 		switch (BPF_SIZE(code)) {
 		case BPF_B:
 			if (is_12b_int(off)) {
@@ -1682,6 +1700,86 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 		emit_sd(RV_REG_T2, 0, RV_REG_T1, ctx);
 		break;
 
+	case BPF_ST | BPF_PROBE_MEM32 | BPF_B:
+	case BPF_ST | BPF_PROBE_MEM32 | BPF_H:
+	case BPF_ST | BPF_PROBE_MEM32 | BPF_W:
+	case BPF_ST | BPF_PROBE_MEM32 | BPF_DW:
+	{
+		int insn_len, insns_start;
+
+		emit_add(RV_REG_T3, rd, RV_REG_ARENA, ctx);
+		rd = RV_REG_T3;
+
+		/* Load imm to a register then store it */
+		emit_imm(RV_REG_T1, imm, ctx);
+
+		switch (BPF_SIZE(code)) {
+		case BPF_B:
+			if (is_12b_int(off)) {
+				insns_start = ctx->ninsns;
+				emit(rv_sb(rd, off, RV_REG_T1), ctx);
+				insn_len = ctx->ninsns - insns_start;
+				break;
+			}
+
+			emit_imm(RV_REG_T2, off, ctx);
+			emit_add(RV_REG_T2, RV_REG_T2, rd, ctx);
+			insns_start = ctx->ninsns;
+			emit(rv_sb(RV_REG_T2, 0, RV_REG_T1), ctx);
+			insn_len = ctx->ninsns - insns_start;
+			break;
+		case BPF_H:
+			if (is_12b_int(off)) {
+				insns_start = ctx->ninsns;
+				emit(rv_sh(rd, off, RV_REG_T1), ctx);
+				insn_len = ctx->ninsns - insns_start;
+				break;
+			}
+
+			emit_imm(RV_REG_T2, off, ctx);
+			emit_add(RV_REG_T2, RV_REG_T2, rd, ctx);
+			insns_start = ctx->ninsns;
+			emit(rv_sh(RV_REG_T2, 0, RV_REG_T1), ctx);
+			insn_len = ctx->ninsns - insns_start;
+			break;
+		case BPF_W:
+			if (is_12b_int(off)) {
+				insns_start = ctx->ninsns;
+				emit_sw(rd, off, RV_REG_T1, ctx);
+				insn_len = ctx->ninsns - insns_start;
+				break;
+			}
+
+			emit_imm(RV_REG_T2, off, ctx);
+			emit_add(RV_REG_T2, RV_REG_T2, rd, ctx);
+			insns_start = ctx->ninsns;
+			emit_sw(RV_REG_T2, 0, RV_REG_T1, ctx);
+			insn_len = ctx->ninsns - insns_start;
+			break;
+		case BPF_DW:
+			if (is_12b_int(off)) {
+				insns_start = ctx->ninsns;
+				emit_sd(rd, off, RV_REG_T1, ctx);
+				insn_len = ctx->ninsns - insns_start;
+				break;
+			}
+
+			emit_imm(RV_REG_T2, off, ctx);
+			emit_add(RV_REG_T2, RV_REG_T2, rd, ctx);
+			insns_start = ctx->ninsns;
+			emit_sd(RV_REG_T2, 0, RV_REG_T1, ctx);
+			insn_len = ctx->ninsns - insns_start;
+			break;
+		}
+
+		ret = add_exception_handler(insn, ctx, REG_DONT_CLEAR_MARKER,
+					    insn_len);
+		if (ret)
+			return ret;
+
+		break;
+	}
+
 	/* STX: *(size *)(dst + off) = src */
 	case BPF_STX | BPF_MEM | BPF_B:
 		if (is_12b_int(off)) {
@@ -1728,6 +1826,84 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 		emit_atomic(rd, rs, off, imm,
 			    BPF_SIZE(code) == BPF_DW, ctx);
 		break;
+
+	case BPF_STX | BPF_PROBE_MEM32 | BPF_B:
+	case BPF_STX | BPF_PROBE_MEM32 | BPF_H:
+	case BPF_STX | BPF_PROBE_MEM32 | BPF_W:
+	case BPF_STX | BPF_PROBE_MEM32 | BPF_DW:
+	{
+		int insn_len, insns_start;
+
+		emit_add(RV_REG_T2, rd, RV_REG_ARENA, ctx);
+		rd = RV_REG_T2;
+
+		switch (BPF_SIZE(code)) {
+		case BPF_B:
+			if (is_12b_int(off)) {
+				insns_start = ctx->ninsns;
+				emit(rv_sb(rd, off, rs), ctx);
+				insn_len = ctx->ninsns - insns_start;
+				break;
+			}
+
+			emit_imm(RV_REG_T1, off, ctx);
+			emit_add(RV_REG_T1, RV_REG_T1, rd, ctx);
+			insns_start = ctx->ninsns;
+			emit(rv_sb(RV_REG_T1, 0, rs), ctx);
+			insn_len = ctx->ninsns - insns_start;
+			break;
+		case BPF_H:
+			if (is_12b_int(off)) {
+				insns_start = ctx->ninsns;
+				emit(rv_sh(rd, off, rs), ctx);
+				insn_len = ctx->ninsns - insns_start;
+				break;
+			}
+
+			emit_imm(RV_REG_T1, off, ctx);
+			emit_add(RV_REG_T1, RV_REG_T1, rd, ctx);
+			insns_start = ctx->ninsns;
+			emit(rv_sh(RV_REG_T1, 0, rs), ctx);
+			insn_len = ctx->ninsns - insns_start;
+			break;
+		case BPF_W:
+			if (is_12b_int(off)) {
+				insns_start = ctx->ninsns;
+				emit_sw(rd, off, rs, ctx);
+				insn_len = ctx->ninsns - insns_start;
+				break;
+			}
+
+			emit_imm(RV_REG_T1, off, ctx);
+			emit_add(RV_REG_T1, RV_REG_T1, rd, ctx);
+			insns_start = ctx->ninsns;
+			emit_sw(RV_REG_T1, 0, rs, ctx);
+			insn_len = ctx->ninsns - insns_start;
+			break;
+		case BPF_DW:
+			if (is_12b_int(off)) {
+				insns_start = ctx->ninsns;
+				emit_sd(rd, off, rs, ctx);
+				insn_len = ctx->ninsns - insns_start;
+				break;
+			}
+
+			emit_imm(RV_REG_T1, off, ctx);
+			emit_add(RV_REG_T1, RV_REG_T1, rd, ctx);
+			insns_start = ctx->ninsns;
+			emit_sd(RV_REG_T1, 0, rs, ctx);
+			insn_len = ctx->ninsns - insns_start;
+			break;
+		}
+
+		ret = add_exception_handler(insn, ctx, REG_DONT_CLEAR_MARKER,
+					    insn_len);
+		if (ret)
+			return ret;
+
+		break;
+	}
+
 	default:
 		pr_err("bpf-jit: unknown opcode %02x\n", code);
 		return -EINVAL;
@@ -1759,6 +1935,8 @@ void bpf_jit_build_prologue(struct rv_jit_context *ctx, bool is_subprog)
 		stack_adjust += 8;
 	if (seen_reg(RV_REG_S6, ctx))
 		stack_adjust += 8;
+	if (ctx->arena_vm_start)
+		stack_adjust += 8;
 
 	stack_adjust = round_up(stack_adjust, 16);
 	stack_adjust += bpf_stack_adjust;
@@ -1810,6 +1988,10 @@ void bpf_jit_build_prologue(struct rv_jit_context *ctx, bool is_subprog)
 		emit_sd(RV_REG_SP, store_offset, RV_REG_S6, ctx);
 		store_offset -= 8;
 	}
+	if (ctx->arena_vm_start) {
+		emit_sd(RV_REG_SP, store_offset, RV_REG_ARENA, ctx);
+		store_offset -= 8;
+	}
 
 	emit_addi(RV_REG_FP, RV_REG_SP, stack_adjust, ctx);
 
@@ -1823,6 +2005,9 @@ void bpf_jit_build_prologue(struct rv_jit_context *ctx, bool is_subprog)
 		emit_mv(RV_REG_TCC_SAVED, RV_REG_TCC, ctx);
 
 	ctx->stack_size = stack_adjust;
+
+	if (ctx->arena_vm_start)
+		emit_imm(RV_REG_ARENA, ctx->arena_vm_start, ctx);
 }
 
 void bpf_jit_build_epilogue(struct rv_jit_context *ctx)

arch/riscv/net/bpf_jit_core.c

@@ -80,6 +80,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 		goto skip_init_ctx;
 	}
 
+	ctx->arena_vm_start = bpf_arena_get_kern_vm_start(prog->aux->arena);
 	ctx->prog = prog;
 	ctx->offset = kcalloc(prog->len, sizeof(int), GFP_KERNEL);
 	if (!ctx->offset) {