bpf: Support new sign-extension load insns

Add interpreter/jit support for new sign-extension load insns
which adds a new mode (BPF_MEMSX).
Also add verifier support to recognize these insns and to
do proper verification with new insns. In verifier, besides
to deduce proper bounds for the dst_reg, probed memory access
is also properly handled.
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20230728011156.3711870-1-yonghong.song@linux.devSigned-off-by: Alexei Starovoitov <ast@kernel.org>

arch/x86/net/bpf_jit_comp.c

@@ -779,6 +779,29 @@ static void emit_ldx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
 	*pprog = prog;
 }
 
+/* LDSX: dst_reg = *(s8*)(src_reg + off) */
+static void emit_ldsx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
+{
+	u8 *prog = *pprog;
+
+	switch (size) {
+	case BPF_B:
+		/* Emit 'movsx rax, byte ptr [rax + off]' */
+		EMIT3(add_2mod(0x48, src_reg, dst_reg), 0x0F, 0xBE);
+		break;
+	case BPF_H:
+		/* Emit 'movsx rax, word ptr [rax + off]' */
+		EMIT3(add_2mod(0x48, src_reg, dst_reg), 0x0F, 0xBF);
+		break;
+	case BPF_W:
+		/* Emit 'movsx rax, dword ptr [rax+0x14]' */
+		EMIT2(add_2mod(0x48, src_reg, dst_reg), 0x63);
+		break;
+	}
+	emit_insn_suffix(&prog, src_reg, dst_reg, off);
+	*pprog = prog;
+}
+
 /* STX: *(u8*)(dst_reg + off) = src_reg */
 static void emit_stx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
 {
@@ -1370,9 +1393,17 @@ st:			if (is_imm8(insn->off))
 		case BPF_LDX | BPF_PROBE_MEM | BPF_W:
 		case BPF_LDX | BPF_MEM | BPF_DW:
 		case BPF_LDX | BPF_PROBE_MEM | BPF_DW:
+			/* LDXS: dst_reg = *(s8*)(src_reg + off) */
+		case BPF_LDX | BPF_MEMSX | BPF_B:
+		case BPF_LDX | BPF_MEMSX | BPF_H:
+		case BPF_LDX | BPF_MEMSX | BPF_W:
+		case BPF_LDX | BPF_PROBE_MEMSX | BPF_B:
+		case BPF_LDX | BPF_PROBE_MEMSX | BPF_H:
+		case BPF_LDX | BPF_PROBE_MEMSX | BPF_W:
 			insn_off = insn->off;
 
-			if (BPF_MODE(insn->code) == BPF_PROBE_MEM) {
+			if (BPF_MODE(insn->code) == BPF_PROBE_MEM ||
+			    BPF_MODE(insn->code) == BPF_PROBE_MEMSX) {
 				/* Conservatively check that src_reg + insn->off is a kernel address:
 				 *   src_reg + insn->off >= TASK_SIZE_MAX + PAGE_SIZE
 				 * src_reg is used as scratch for src_reg += insn->off and restored
@@ -1415,8 +1446,13 @@ st:			if (is_imm8(insn->off))
 				start_of_ldx = prog;
 				end_of_jmp[-1] = start_of_ldx - end_of_jmp;
 			}
+			if (BPF_MODE(insn->code) == BPF_PROBE_MEMSX ||
+			    BPF_MODE(insn->code) == BPF_MEMSX)
+				emit_ldsx(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn_off);
+			else
 				emit_ldx(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn_off);
-			if (BPF_MODE(insn->code) == BPF_PROBE_MEM) {
+			if (BPF_MODE(insn->code) == BPF_PROBE_MEM ||
+			    BPF_MODE(insn->code) == BPF_PROBE_MEMSX) {
 				struct exception_table_entry *ex;
 				u8 *_insn = image + proglen + (start_of_ldx - temp);
 				s64 delta;

include/linux/filter.h

@@ -69,6 +69,9 @@ struct ctl_table_header;
 /* unused opcode to mark special load instruction. Same as BPF_ABS */
 #define BPF_PROBE_MEM	0x20
 
+/* unused opcode to mark special ldsx instruction. Same as BPF_IND */
+#define BPF_PROBE_MEMSX	0x40
+
 /* unused opcode to mark call to interpreter with arguments */
 #define BPF_CALL_ARGS	0xe0
 

include/uapi/linux/bpf.h

@@ -19,6 +19,7 @@
 
 /* ld/ldx fields */
 #define BPF_DW		0x18	/* double word (64-bit) */
+#define BPF_MEMSX	0x80	/* load with sign extension */
 #define BPF_ATOMIC	0xc0	/* atomic memory ops - op type in immediate */
 #define BPF_XADD	0xc0	/* exclusive add - legacy name */
 

kernel/bpf/core.c

@@ -1610,6 +1610,9 @@ EXPORT_SYMBOL_GPL(__bpf_call_base);
 	INSN_3(LDX, MEM, H),			\
 	INSN_3(LDX, MEM, W),			\
 	INSN_3(LDX, MEM, DW),			\
+	INSN_3(LDX, MEMSX, B),			\
+	INSN_3(LDX, MEMSX, H),			\
+	INSN_3(LDX, MEMSX, W),			\
 	/*   Immediate based. */		\
 	INSN_3(LD, IMM, DW)
 
@@ -1666,6 +1669,9 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
 		[BPF_LDX | BPF_PROBE_MEM | BPF_H] = &&LDX_PROBE_MEM_H,
 		[BPF_LDX | BPF_PROBE_MEM | BPF_W] = &&LDX_PROBE_MEM_W,
 		[BPF_LDX | BPF_PROBE_MEM | BPF_DW] = &&LDX_PROBE_MEM_DW,
+		[BPF_LDX | BPF_PROBE_MEMSX | BPF_B] = &&LDX_PROBE_MEMSX_B,
+		[BPF_LDX | BPF_PROBE_MEMSX | BPF_H] = &&LDX_PROBE_MEMSX_H,
+		[BPF_LDX | BPF_PROBE_MEMSX | BPF_W] = &&LDX_PROBE_MEMSX_W,
 	};
 #undef BPF_INSN_3_LBL
 #undef BPF_INSN_2_LBL
@@ -1942,6 +1948,21 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
 	LDST(DW, u64)
 #undef LDST
 
+#define LDSX(SIZEOP, SIZE)						\
+	LDX_MEMSX_##SIZEOP:						\
+		DST = *(SIZE *)(unsigned long) (SRC + insn->off);	\
+		CONT;							\
+	LDX_PROBE_MEMSX_##SIZEOP:					\
+		bpf_probe_read_kernel(&DST, sizeof(SIZE),		\
+				      (const void *)(long) (SRC + insn->off));	\
+		DST = *((SIZE *)&DST);					\
+		CONT;
+
+	LDSX(B,   s8)
+	LDSX(H,  s16)
+	LDSX(W,  s32)
+#undef LDSX
+
 #define ATOMIC_ALU_OP(BOP, KOP)						\
 		case BOP:						\
 			if (BPF_SIZE(insn->code) == BPF_W)		\

kernel/bpf/verifier.c

@@ -5827,6 +5827,84 @@ static void coerce_reg_to_size(struct bpf_reg_state *reg, int size)
 	__reg_combine_64_into_32(reg);
 }
 
+static void set_sext64_default_val(struct bpf_reg_state *reg, int size)
+{
+	if (size == 1) {
+		reg->smin_value = reg->s32_min_value = S8_MIN;
+		reg->smax_value = reg->s32_max_value = S8_MAX;
+	} else if (size == 2) {
+		reg->smin_value = reg->s32_min_value = S16_MIN;
+		reg->smax_value = reg->s32_max_value = S16_MAX;
+	} else {
+		/* size == 4 */
+		reg->smin_value = reg->s32_min_value = S32_MIN;
+		reg->smax_value = reg->s32_max_value = S32_MAX;
+	}
+	reg->umin_value = reg->u32_min_value = 0;
+	reg->umax_value = U64_MAX;
+	reg->u32_max_value = U32_MAX;
+	reg->var_off = tnum_unknown;
+}
+
+static void coerce_reg_to_size_sx(struct bpf_reg_state *reg, int size)
+{
+	s64 init_s64_max, init_s64_min, s64_max, s64_min, u64_cval;
+	u64 top_smax_value, top_smin_value;
+	u64 num_bits = size * 8;
+
+	if (tnum_is_const(reg->var_off)) {
+		u64_cval = reg->var_off.value;
+		if (size == 1)
+			reg->var_off = tnum_const((s8)u64_cval);
+		else if (size == 2)
+			reg->var_off = tnum_const((s16)u64_cval);
+		else
+			/* size == 4 */
+			reg->var_off = tnum_const((s32)u64_cval);
+
+		u64_cval = reg->var_off.value;
+		reg->smax_value = reg->smin_value = u64_cval;
+		reg->umax_value = reg->umin_value = u64_cval;
+		reg->s32_max_value = reg->s32_min_value = u64_cval;
+		reg->u32_max_value = reg->u32_min_value = u64_cval;
+		return;
+	}
+
+	top_smax_value = ((u64)reg->smax_value >> num_bits) << num_bits;
+	top_smin_value = ((u64)reg->smin_value >> num_bits) << num_bits;
+
+	if (top_smax_value != top_smin_value)
+		goto out;
+
+	/* find the s64_min and s64_min after sign extension */
+	if (size == 1) {
+		init_s64_max = (s8)reg->smax_value;
+		init_s64_min = (s8)reg->smin_value;
+	} else if (size == 2) {
+		init_s64_max = (s16)reg->smax_value;
+		init_s64_min = (s16)reg->smin_value;
+	} else {
+		init_s64_max = (s32)reg->smax_value;
+		init_s64_min = (s32)reg->smin_value;
+	}
+
+	s64_max = max(init_s64_max, init_s64_min);
+	s64_min = min(init_s64_max, init_s64_min);
+
+	/* both of s64_max/s64_min positive or negative */
+	if (s64_max >= 0 == s64_min >= 0) {
+		reg->smin_value = reg->s32_min_value = s64_min;
+		reg->smax_value = reg->s32_max_value = s64_max;
+		reg->umin_value = reg->u32_min_value = s64_min;
+		reg->umax_value = reg->u32_max_value = s64_max;
+		reg->var_off = tnum_range(s64_min, s64_max);
+		return;
+	}
+
+out:
+	set_sext64_default_val(reg, size);
+}
+
 static bool bpf_map_is_rdonly(const struct bpf_map *map)
 {
 	/* A map is considered read-only if the following condition are true:
@@ -5847,7 +5925,8 @@ static bool bpf_map_is_rdonly(const struct bpf_map *map)
 	       !bpf_map_write_active(map);
 }
 
-static int bpf_map_direct_read(struct bpf_map *map, int off, int size, u64 *val)
+static int bpf_map_direct_read(struct bpf_map *map, int off, int size, u64 *val,
+			       bool is_ldsx)
 {
 	void *ptr;
 	u64 addr;
@@ -5860,13 +5939,13 @@ static int bpf_map_direct_read(struct bpf_map *map, int off, int size, u64 *val)
 
 	switch (size) {
 	case sizeof(u8):
-		*val = (u64)*(u8 *)ptr;
+		*val = is_ldsx ? (s64)*(s8 *)ptr : (u64)*(u8 *)ptr;
 		break;
 	case sizeof(u16):
-		*val = (u64)*(u16 *)ptr;
+		*val = is_ldsx ? (s64)*(s16 *)ptr : (u64)*(u16 *)ptr;
 		break;
 	case sizeof(u32):
-		*val = (u64)*(u32 *)ptr;
+		*val = is_ldsx ? (s64)*(s32 *)ptr : (u64)*(u32 *)ptr;
 		break;
 	case sizeof(u64):
 		*val = *(u64 *)ptr;
@@ -6285,7 +6364,7 @@ static int check_stack_access_within_bounds(
  */
 static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regno,
 			    int off, int bpf_size, enum bpf_access_type t,
-			    int value_regno, bool strict_alignment_once)
+			    int value_regno, bool strict_alignment_once, bool is_ldsx)
 {
 	struct bpf_reg_state *regs = cur_regs(env);
 	struct bpf_reg_state *reg = regs + regno;
@@ -6346,7 +6425,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
 				u64 val = 0;
 
 				err = bpf_map_direct_read(map, map_off, size,
-							  &val);
+							  &val, is_ldsx);
 				if (err)
 					return err;
 
@@ -6516,8 +6595,11 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
 
 	if (!err && size < BPF_REG_SIZE && value_regno >= 0 && t == BPF_READ &&
 	    regs[value_regno].type == SCALAR_VALUE) {
+		if (!is_ldsx)
 			/* b/h/w load zero-extends, mark upper bits as known 0 */
 			coerce_reg_to_size(&regs[value_regno], size);
+		else
+			coerce_reg_to_size_sx(&regs[value_regno], size);
 	}
 	return err;
 }
@@ -6609,17 +6691,17 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
 	 * case to simulate the register fill.
 	 */
 	err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
-			       BPF_SIZE(insn->code), BPF_READ, -1, true);
+			       BPF_SIZE(insn->code), BPF_READ, -1, true, false);
 	if (!err && load_reg >= 0)
 		err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
 				       BPF_SIZE(insn->code), BPF_READ, load_reg,
-				       true);
+				       true, false);
 	if (err)
 		return err;
 
 	/* Check whether we can write into the same memory. */
 	err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
-			       BPF_SIZE(insn->code), BPF_WRITE, -1, true);
+			       BPF_SIZE(insn->code), BPF_WRITE, -1, true, false);
 	if (err)
 		return err;
 
@@ -6865,7 +6947,7 @@ static int check_helper_mem_access(struct bpf_verifier_env *env, int regno,
 				return zero_size_allowed ? 0 : -EACCES;
 
 			return check_mem_access(env, env->insn_idx, regno, offset, BPF_B,
-						atype, -1, false);
+						atype, -1, false, false);
 		}
 
 		fallthrough;
@@ -7237,7 +7319,7 @@ static int process_dynptr_func(struct bpf_verifier_env *env, int regno, int insn
 		/* we write BPF_DW bits (8 bytes) at a time */
 		for (i = 0; i < BPF_DYNPTR_SIZE; i += 8) {
 			err = check_mem_access(env, insn_idx, regno,
-					       i, BPF_DW, BPF_WRITE, -1, false);
+					       i, BPF_DW, BPF_WRITE, -1, false, false);
 			if (err)
 				return err;
 		}
@@ -7330,7 +7412,7 @@ static int process_iter_arg(struct bpf_verifier_env *env, int regno, int insn_id
 
 		for (i = 0; i < nr_slots * 8; i += BPF_REG_SIZE) {
 			err = check_mem_access(env, insn_idx, regno,
-					       i, BPF_DW, BPF_WRITE, -1, false);
+					       i, BPF_DW, BPF_WRITE, -1, false, false);
 			if (err)
 				return err;
 		}
@@ -9474,7 +9556,7 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
 	 */
 	for (i = 0; i < meta.access_size; i++) {
 		err = check_mem_access(env, insn_idx, meta.regno, i, BPF_B,
-				       BPF_WRITE, -1, false);
+				       BPF_WRITE, -1, false, false);
 		if (err)
 			return err;
 	}
@@ -16202,7 +16284,7 @@ static int save_aux_ptr_type(struct bpf_verifier_env *env, enum bpf_reg_type typ
 			 * Have to support a use case when one path through
 			 * the program yields TRUSTED pointer while another
 			 * is UNTRUSTED. Fallback to UNTRUSTED to generate
-			 * BPF_PROBE_MEM.
+			 * BPF_PROBE_MEM/BPF_PROBE_MEMSX.
 			 */
 			*prev_type = PTR_TO_BTF_ID | PTR_UNTRUSTED;
 		} else {
@@ -16343,7 +16425,8 @@ static int do_check(struct bpf_verifier_env *env)
 			 */
 			err = check_mem_access(env, env->insn_idx, insn->src_reg,
 					       insn->off, BPF_SIZE(insn->code),
-					       BPF_READ, insn->dst_reg, false);
+					       BPF_READ, insn->dst_reg, false,
+					       BPF_MODE(insn->code) == BPF_MEMSX);
 			if (err)
 				return err;
 
@@ -16380,7 +16463,7 @@ static int do_check(struct bpf_verifier_env *env)
 			/* check that memory (dst_reg + off) is writeable */
 			err = check_mem_access(env, env->insn_idx, insn->dst_reg,
 					       insn->off, BPF_SIZE(insn->code),
-					       BPF_WRITE, insn->src_reg, false);
+					       BPF_WRITE, insn->src_reg, false, false);
 			if (err)
 				return err;
 
@@ -16405,7 +16488,7 @@ static int do_check(struct bpf_verifier_env *env)
 			/* check that memory (dst_reg + off) is writeable */
 			err = check_mem_access(env, env->insn_idx, insn->dst_reg,
 					       insn->off, BPF_SIZE(insn->code),
-					       BPF_WRITE, -1, false);
+					       BPF_WRITE, -1, false, false);
 			if (err)
 				return err;
 
@@ -16833,7 +16916,8 @@ static int resolve_pseudo_ldimm64(struct bpf_verifier_env *env)
 
 	for (i = 0; i < insn_cnt; i++, insn++) {
 		if (BPF_CLASS(insn->code) == BPF_LDX &&
-		    (BPF_MODE(insn->code) != BPF_MEM || insn->imm != 0)) {
+		    ((BPF_MODE(insn->code) != BPF_MEM && BPF_MODE(insn->code) != BPF_MEMSX) ||
+		    insn->imm != 0)) {
 			verbose(env, "BPF_LDX uses reserved fields\n");
 			return -EINVAL;
 		}
@@ -17531,7 +17615,10 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 		if (insn->code == (BPF_LDX | BPF_MEM | BPF_B) ||
 		    insn->code == (BPF_LDX | BPF_MEM | BPF_H) ||
 		    insn->code == (BPF_LDX | BPF_MEM | BPF_W) ||
-		    insn->code == (BPF_LDX | BPF_MEM | BPF_DW)) {
+		    insn->code == (BPF_LDX | BPF_MEM | BPF_DW) ||
+		    insn->code == (BPF_LDX | BPF_MEMSX | BPF_B) ||
+		    insn->code == (BPF_LDX | BPF_MEMSX | BPF_H) ||
+		    insn->code == (BPF_LDX | BPF_MEMSX | BPF_W)) {
 			type = BPF_READ;
 		} else if (insn->code == (BPF_STX | BPF_MEM | BPF_B) ||
 			   insn->code == (BPF_STX | BPF_MEM | BPF_H) ||
@@ -17590,8 +17677,12 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 		 */
 		case PTR_TO_BTF_ID | MEM_ALLOC | PTR_UNTRUSTED:
 			if (type == BPF_READ) {
+				if (BPF_MODE(insn->code) == BPF_MEM)
 					insn->code = BPF_LDX | BPF_PROBE_MEM |
 						     BPF_SIZE((insn)->code);
+				else
+					insn->code = BPF_LDX | BPF_PROBE_MEMSX |
+						     BPF_SIZE((insn)->code);
 				env->prog->aux->num_exentries++;
 			}
 			continue;
@@ -17779,7 +17870,8 @@ static int jit_subprogs(struct bpf_verifier_env *env)
 		insn = func[i]->insnsi;
 		for (j = 0; j < func[i]->len; j++, insn++) {
 			if (BPF_CLASS(insn->code) == BPF_LDX &&
-			    BPF_MODE(insn->code) == BPF_PROBE_MEM)
+			    (BPF_MODE(insn->code) == BPF_PROBE_MEM ||
+			     BPF_MODE(insn->code) == BPF_PROBE_MEMSX))
 				num_exentries++;
 		}
 		func[i]->aux->num_exentries = num_exentries;

tools/include/uapi/linux/bpf.h

@@ -19,6 +19,7 @@
 
 /* ld/ldx fields */
 #define BPF_DW		0x18	/* double word (64-bit) */
+#define BPF_MEMSX	0x80	/* load with sign extension */
 #define BPF_ATOMIC	0xc0	/* atomic memory ops - op type in immediate */
 #define BPF_XADD	0xc0	/* exclusive add - legacy name */