path: root/include/linux/bpf_verifier.h

/* SPDX-License-Identifier: GPL-2.0-only */
/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
 */
#ifndef _LINUX_BPF_VERIFIER_H
#define _LINUX_BPF_VERIFIER_H 1

#include <linux/bpf.h> /* for enum bpf_reg_type */
#include <linux/btf.h> /* for struct btf and btf_id() */
#include <linux/filter.h> /* for MAX_BPF_STACK */
#include <linux/tnum.h>

/* Maximum variable offset umax_value permitted when resolving memory accesses.
 * In practice this is far bigger than any realistic pointer offset; this limit
 * ensures that umax_value + (int)off + (int)size cannot overflow a u64.
 */
#define BPF_MAX_VAR_OFF	(1 << 29)
/* Maximum variable size permitted for ARG_CONST_SIZE[_OR_ZERO].  This ensures
 * that converting umax_value to int cannot overflow.
 */
#define BPF_MAX_VAR_SIZ	(1 << 29)
/* size of tmp_str_buf in bpf_verifier.
 * we need at least 306 bytes to fit full stack mask representation
 * (in the "-8,-16,...,-512" form)
 */
#define TMP_STR_BUF_LEN 320

/* Liveness marks, used for registers and spilled-regs (in stack slots).
 * Read marks propagate upwards until they find a write mark; they record that
 * "one of this state's descendants read this reg" (and therefore the reg is
 * relevant for states_equal() checks).
 * Write marks collect downwards and do not propagate; they record that "the
 * straight-line code that reached this state (from its parent) wrote this reg"
 * (and therefore that reads propagated from this state or its descendants
 * should not propagate to its parent).
 * A state with a write mark can receive read marks; it just won't propagate
 * them to its parent, since the write mark is a property, not of the state,
 * but of the link between it and its parent.  See mark_reg_read() and
 * mark_stack_slot_read() in kernel/bpf/verifier.c.
 */
enum bpf_reg_liveness {
	REG_LIVE_NONE = 0, /* reg hasn't been read or written this branch */
	REG_LIVE_READ32 = 0x1, /* reg was read, so we're sensitive to initial value */
	REG_LIVE_READ64 = 0x2, /* likewise, but full 64-bit content matters */
	REG_LIVE_READ = REG_LIVE_READ32 | REG_LIVE_READ64,
	REG_LIVE_WRITTEN = 0x4, /* reg was written first, screening off later reads */
	REG_LIVE_DONE = 0x8, /* liveness won't be updating this register anymore */
};

/* For every reg representing a map value or allocated object pointer,
 * we consider the tuple of (ptr, id) for them to be unique in verifier
 * context and conside them to not alias each other for the purposes of
 * tracking lock state.
 */
struct bpf_active_lock {
	/* This can either be reg->map_ptr or reg->btf. If ptr is NULL,
	 * there's no active lock held, and other fields have no
	 * meaning. If non-NULL, it indicates that a lock is held and
	 * id member has the reg->id of the register which can be >= 0.
	 */
	void *ptr;
	/* This will be reg->id */
	u32 id;
};

#define ITER_PREFIX "bpf_iter_"

enum bpf_iter_state {
	BPF_ITER_STATE_INVALID, /* for non-first slot */
	BPF_ITER_STATE_ACTIVE,
	BPF_ITER_STATE_DRAINED,
};

struct bpf_reg_state {
	/* Ordering of fields matters.  See states_equal() */
	enum bpf_reg_type type;
	/* Fixed part of pointer offset, pointer types only */
	s32 off;
	union {
		/* valid when type == PTR_TO_PACKET */
		int range;

		/* valid when type == CONST_PTR_TO_MAP | PTR_TO_MAP_VALUE |
		 *   PTR_TO_MAP_VALUE_OR_NULL
		 */
		struct {
			struct bpf_map *map_ptr;
			/* To distinguish map lookups from outer map
			 * the map_uid is non-zero for registers
			 * pointing to inner maps.
			 */
			u32 map_uid;
		};

		/* for PTR_TO_BTF_ID */
		struct {
			struct btf *btf;
			u32 btf_id;
		};

		struct { /* for PTR_TO_MEM | PTR_TO_MEM_OR_NULL */
			u32 mem_size;
			u32 dynptr_id; /* for dynptr slices */
		};

		/* For dynptr stack slots */
		struct {
			enum bpf_dynptr_type type;
			/* A dynptr is 16 bytes so it takes up 2 stack slots.
			 * We need to track which slot is the first slot
			 * to protect against cases where the user may try to
			 * pass in an address starting at the second slot of the
			 * dynptr.
			 */
			bool first_slot;
		} dynptr;

		/* For bpf_iter stack slots */
		struct {
			/* BTF container and BTF type ID describing
			 * struct bpf_iter_<type> of an iterator state
			 */
			struct btf *btf;
			u32 btf_id;
			/* packing following two fields to fit iter state into 16 bytes */
			enum bpf_iter_state state:2;
			int depth:30;
		} iter;

		/* Max size from any of the above. */
		struct {
			unsigned long raw1;
			unsigned long raw2;
		} raw;

		u32 subprogno; /* for PTR_TO_FUNC */
	};
	/* For scalar types (SCALAR_VALUE), this represents our knowledge of
	 * the actual value.
	 * For pointer types, this represents the variable part of the offset
	 * from the pointed-to object, and is shared with all bpf_reg_states
	 * with the same id as us.
	 */
	struct tnum var_off;
	/* Used to determine if any memory access using this register will
	 * result in a bad access.
	 * These refer to the same value as var_off, not necessarily the actual
	 * contents of the register.
	 */
	s64 smin_value; /* minimum possible (s64)value */
	s64 smax_value; /* maximum possible (s64)value */
	u64 umin_value; /* minimum possible (u64)value */
	u64 umax_value; /* maximum possible (u64)value */
	s32 s32_min_value; /* minimum possible (s32)value */
	s32 s32_max_value; /* maximum possible (s32)value */
	u32 u32_min_value; /* minimum possible (u32)value */
	u32 u32_max_value; /* maximum possible (u32)value */
	/* For PTR_TO_PACKET, used to find other pointers with the same variable
	 * offset, so they can share range knowledge.
	 * For PTR_TO_MAP_VALUE_OR_NULL this is used to share which map value we
	 * came from, when one is tested for != NULL.
	 * For PTR_TO_MEM_OR_NULL this is used to identify memory allocation
	 * for the purpose of tracking that it's freed.
	 * For PTR_TO_SOCKET this is used to share which pointers retain the
	 * same reference to the socket, to determine proper reference freeing.
	 * For stack slots that are dynptrs, this is used to track references to
	 * the dynptr to determine proper reference freeing.
	 * Similarly to dynptrs, we use ID to track "belonging" of a reference
	 * to a specific instance of bpf_iter.
	 */
	u32 id;
	/* PTR_TO_SOCKET and PTR_TO_TCP_SOCK could be a ptr returned
	 * from a pointer-cast helper, bpf_sk_fullsock() and
	 * bpf_tcp_sock().
	 *
	 * Consider the following where "sk" is a reference counted
	 * pointer returned from "sk = bpf_sk_lookup_tcp();":
	 *
	 * 1: sk = bpf_sk_lookup_tcp();
	 * 2: if (!sk) { return 0; }
	 * 3: fullsock = bpf_sk_fullsock(sk);
	 * 4: if (!fullsock) { bpf_sk_release(sk); return 0; }
	 * 5: tp = bpf_tcp_sock(fullsock);
	 * 6: if (!tp) { bpf_sk_release(sk); return 0; }
	 * 7: bpf_sk_release(sk);
	 * 8: snd_cwnd = tp->snd_cwnd;  // verifier will complain
	 *
	 * After bpf_sk_release(sk) at line 7, both "fullsock" ptr and
	 * "tp" ptr should be invalidated also.  In order to do that,
	 * the reg holding "fullsock" and "sk" need to remember
	 * the original refcounted ptr id (i.e. sk_reg->id) in ref_obj_id
	 * such that the verifier can reset all regs which have
	 * ref_obj_id matching the sk_reg->id.
	 *
	 * sk_reg->ref_obj_id is set to sk_reg->id at line 1.
	 * sk_reg->id will stay as NULL-marking purpose only.
	 * After NULL-marking is done, sk_reg->id can be reset to 0.
	 *
	 * After "fullsock = bpf_sk_fullsock(sk);" at line 3,
	 * fullsock_reg->ref_obj_id is set to sk_reg->ref_obj_id.
	 *
	 * After "tp = bpf_tcp_sock(fullsock);" at line 5,
	 * tp_reg->ref_obj_id is set to fullsock_reg->ref_obj_id
	 * which is the same as sk_reg->ref_obj_id.
	 *
	 * From the verifier perspective, if sk, fullsock and tp
	 * are not NULL, they are the same ptr with different
	 * reg->type.  In particular, bpf_sk_release(tp) is also
	 * allowed and has the same effect as bpf_sk_release(sk).
	 */
	u32 ref_obj_id;
	/* parentage chain for liveness checking */
	struct bpf_reg_state *parent;
	/* Inside the callee two registers can be both PTR_TO_STACK like
	 * R1=fp-8 and R2=fp-8, but one of them points to this function stack
	 * while another to the caller's stack. To differentiate them 'frameno'
	 * is used which is an index in bpf_verifier_state->frame[] array
	 * pointing to bpf_func_state.
	 */
	u32 frameno;
	/* Tracks subreg definition. The stored value is the insn_idx of the
	 * writing insn. This is safe because subreg_def is used before any insn
	 * patching which only happens after main verification finished.
	 */
	s32 subreg_def;
	enum bpf_reg_liveness live;
	/* if (!precise && SCALAR_VALUE) min/max/tnum don't affect safety */
	bool precise;
};

enum bpf_stack_slot_type {
	STACK_INVALID,    /* nothing was stored in this stack slot */
	STACK_SPILL,      /* register spilled into stack */
	STACK_MISC,	  /* BPF program wrote some data into this slot */
	STACK_ZERO,	  /* BPF program wrote constant zero */
	/* A dynptr is stored in this stack slot. The type of dynptr
	 * is stored in bpf_stack_state->spilled_ptr.dynptr.type
	 */
	STACK_DYNPTR,
	STACK_ITER,
};

#define BPF_REG_SIZE 8	/* size of eBPF register in bytes */

#define BPF_REGMASK_ARGS ((1 << BPF_REG_1) | (1 << BPF_REG_2) | \
			  (1 << BPF_REG_3) | (1 << BPF_REG_4) | \
			  (1 << BPF_REG_5))

#define BPF_DYNPTR_SIZE		sizeof(struct bpf_dynptr_kern)
#define BPF_DYNPTR_NR_SLOTS		(BPF_DYNPTR_SIZE / BPF_REG_SIZE)

struct bpf_stack_state {
	struct bpf_reg_state spilled_ptr;
	u8 slot_type[BPF_REG_SIZE];
};

struct bpf_reference_state {
	/* Track each reference created with a unique id, even if the same
	 * instruction creates the reference multiple times (eg, via CALL).
	 */
	int id;
	/* Instruction where the allocation of this reference occurred. This
	 * is used purely to inform the user of a reference leak.
	 */
	int insn_idx;
	/* There can be a case like:
	 * main (frame 0)
	 *  cb (frame 1)
	 *   func (frame 3)
	 *    cb (frame 4)
	 * Hence for frame 4, if callback_ref just stored boolean, it would be
	 * impossible to distinguish nested callback refs. Hence store the
	 * frameno and compare that to callback_ref in check_reference_leak when
	 * exiting a callback function.
	 */
	int callback_ref;
};

struct bpf_retval_range {
	s32 minval;
	s32 maxval;
};

/* state of the program:
 * type of all registers and stack info
 */
struct bpf_func_state {
	struct bpf_reg_state regs[MAX_BPF_REG];
	/* index of call instruction that called into this func */
	int callsite;
	/* stack frame number of this function state from pov of
	 * enclosing bpf_verifier_state.
	 * 0 = main function, 1 = first callee.
	 */
	u32 frameno;
	/* subprog number == index within subprog_info
	 * zero == main subprog
	 */
	u32 subprogno;
	/* Every bpf_timer_start will increment async_entry_cnt.
	 * It's used to distinguish:
	 * void foo(void) { for(;;); }
	 * void foo(void) { bpf_timer_set_callback(,foo); }
	 */
	u32 async_entry_cnt;
	struct bpf_retval_range callback_ret_range;
	bool in_callback_fn;
	bool in_async_callback_fn;
	bool in_exception_callback_fn;
	/* For callback calling functions that limit number of possible
	 * callback executions (e.g. bpf_loop) keeps track of current
	 * simulated iteration number.
	 * Value in frame N refers to number of times callback with frame
	 * N+1 was simulated, e.g. for the following call:
	 *
	 *   bpf_loop(..., fn, ...); | suppose current frame is N
	 *                           | fn would be simulated in frame N+1
	 *                           | number of simulations is tracked in frame N
	 */
	u32 callback_depth;

	/* The following fields should be last. See copy_func_state() */
	int acquired_refs;
	struct bpf_reference_state *refs;
	/* The state of the stack. Each element of the array describes BPF_REG_SIZE
	 * (i.e. 8) bytes worth of stack memory.
	 * stack[0] represents bytes [*(r10-8)..*(r10-1)]
	 * stack[1] represents bytes [*(r10-16)..*(r10-9)]
	 * ...