Merge branch 'bpf-rewrite-value-tracking-in-verifier'

Edward Cree says:

====================
bpf: rewrite value tracking in verifier

This series simplifies alignment tracking, generalises bounds tracking
and fixes some bounds-tracking bugs in the BPF verifier.  Pointer
arithmetic on packet pointers, stack pointers, map value pointers and
context pointers has been unified, and bounds on these pointers are
only checked when the pointer is dereferenced.

Operations on pointers which destroy all relation to the original
pointer (such as multiplies and shifts) are disallowed if
!env->allow_ptr_leaks, otherwise they convert the pointer to an
unknown scalar and feed it to the normal scalar arithmetic handling.

Pointer types have been unified with the corresponding
adjusted-pointer types where those existed
(e.g. PTR_TO_MAP_VALUE[_ADJ] or FRAME_PTR vs PTR_TO_STACK); similarly,
CONST_IMM and UNKNOWN_VALUE have been unified into SCALAR_VALUE.

Pointer types (except CONST_PTR_TO_MAP, PTR_TO_MAP_VALUE_OR_NULL and
PTR_TO_PACKET_END, which do not allow arithmetic) have a 'fixed
offset' and a 'variable offset'; the former is used when e.g. adding
an immediate or a known-constant register, as long as it does not
overflow.  Otherwise the latter is used, and any operation creating a
new variable offset creates a new 'id' (and, for PTR_TO_PACKET, clears
the 'range').  SCALAR_VALUEs use the 'variable offset' fields to track
the range of possible values; the 'fixed offset' should never be set
on a scalar.
====================
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/netronome/nfp/bpf/verifier.c

@@ -79,28 +79,32 @@ nfp_bpf_check_exit(struct nfp_prog *nfp_prog,
 		   const struct bpf_verifier_env *env)
 {
 	const struct bpf_reg_state *reg0 = &env->cur_state.regs[0];
+	u64 imm;
 
 	if (nfp_prog->act == NN_ACT_XDP)
 		return 0;
 
-	if (reg0->type != CONST_IMM) {
-		pr_info("unsupported exit state: %d, imm: %llx\n",
-			reg0->type, reg0->imm);
+	if (!(reg0->type == SCALAR_VALUE && tnum_is_const(reg0->var_off))) {
+		char tn_buf[48];
+
+		tnum_strn(tn_buf, sizeof(tn_buf), reg0->var_off);
+		pr_info("unsupported exit state: %d, var_off: %s\n",
+			reg0->type, tn_buf);
 		return -EINVAL;
 	}
 
-	if (nfp_prog->act != NN_ACT_DIRECT &&
-	    reg0->imm != 0 && (reg0->imm & ~0U) != ~0U) {
+	imm = reg0->var_off.value;
+	if (nfp_prog->act != NN_ACT_DIRECT && imm != 0 && (imm & ~0U) != ~0U) {
 		pr_info("unsupported exit state: %d, imm: %llx\n",
-			reg0->type, reg0->imm);
+			reg0->type, imm);
 		return -EINVAL;
 	}
 
-	if (nfp_prog->act == NN_ACT_DIRECT && reg0->imm <= TC_ACT_REDIRECT &&
-	    reg0->imm != TC_ACT_SHOT && reg0->imm != TC_ACT_STOLEN &&
-	    reg0->imm != TC_ACT_QUEUED) {
+	if (nfp_prog->act == NN_ACT_DIRECT && imm <= TC_ACT_REDIRECT &&
+	    imm != TC_ACT_SHOT && imm != TC_ACT_STOLEN &&
+	    imm != TC_ACT_QUEUED) {
 		pr_info("unsupported exit state: %d, imm: %llx\n",
-			reg0->type, reg0->imm);
+			reg0->type, imm);
 		return -EINVAL;
 	}
 

include/linux/bpf.h

@@ -117,35 +117,25 @@ enum bpf_access_type {
 };
 
 /* types of values stored in eBPF registers */
+/* Pointer types represent:
+ * pointer
+ * pointer + imm
+ * pointer + (u16) var
+ * pointer + (u16) var + imm
+ * if (range > 0) then [ptr, ptr + range - off) is safe to access
+ * if (id > 0) means that some 'var' was added
+ * if (off > 0) means that 'imm' was added
+ */
 enum bpf_reg_type {
 	NOT_INIT = 0,		 /* nothing was written into register */
-	UNKNOWN_VALUE,		 /* reg doesn't contain a valid pointer */
+	SCALAR_VALUE,		 /* reg doesn't contain a valid pointer */
 	PTR_TO_CTX,		 /* reg points to bpf_context */
 	CONST_PTR_TO_MAP,	 /* reg points to struct bpf_map */
 	PTR_TO_MAP_VALUE,	 /* reg points to map element value */
 	PTR_TO_MAP_VALUE_OR_NULL,/* points to map elem value or NULL */
-	FRAME_PTR,		 /* reg == frame_pointer */
-	PTR_TO_STACK,		 /* reg == frame_pointer + imm */
-	CONST_IMM,		 /* constant integer value */
-
-	/* PTR_TO_PACKET represents:
-	 * skb->data
-	 * skb->data + imm
-	 * skb->data + (u16) var
-	 * skb->data + (u16) var + imm
-	 * if (range > 0) then [ptr, ptr + range - off) is safe to access
-	 * if (id > 0) means that some 'var' was added
-	 * if (off > 0) menas that 'imm' was added
-	 */
-	PTR_TO_PACKET,
+	PTR_TO_STACK,		 /* reg == frame_pointer + offset */
+	PTR_TO_PACKET,		 /* reg points to skb->data */
 	PTR_TO_PACKET_END,	 /* skb->data + headlen */
-
-	/* PTR_TO_MAP_VALUE_ADJ is used for doing pointer math inside of a map
-	 * elem value.  We only allow this if we can statically verify that
-	 * access from this register are going to fall within the size of the
-	 * map element.
-	 */
-	PTR_TO_MAP_VALUE_ADJ,
 };
 
 struct bpf_prog;

include/linux/bpf_verifier.h

@@ -9,41 +9,54 @@
 
 #include <linux/bpf.h> /* for enum bpf_reg_type */
 #include <linux/filter.h> /* for MAX_BPF_STACK */
+#include <linux/tnum.h>
 
- /* Just some arbitrary values so we can safely do math without overflowing and
-  * are obviously wrong for any sort of memory access.
-  */
-#define BPF_REGISTER_MAX_RANGE (1024 * 1024 * 1024)
-#define BPF_REGISTER_MIN_RANGE -1
+/* 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	(1ULL << 31)
+/* 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	INT_MAX
 
 struct bpf_reg_state {
 	enum bpf_reg_type type;
 	union {
-		/* valid when type == CONST_IMM | PTR_TO_STACK | UNKNOWN_VALUE */
-		s64 imm;
-
-		/* valid when type == PTR_TO_PACKET* */
-		struct {
-			u16 off;
-			u16 range;
-		};
+		/* valid when type == PTR_TO_PACKET */
+		u16 range;
 
 		/* valid when type == CONST_PTR_TO_MAP | PTR_TO_MAP_VALUE |
 		 *   PTR_TO_MAP_VALUE_OR_NULL
 		 */
 		struct bpf_map *map_ptr;
 	};
+	/* Fixed part of pointer offset, pointer types only */
+	s32 off;
+	/* 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.
+	 */
 	u32 id;
+	/* These five fields must be last.  See states_equal() */
+	/* 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 two fields must be last.
-	 * See states_equal()
+	 * result in a bad access.
+	 * These refer to the same value as var_off, not necessarily the actual
+	 * contents of the register.
 	 */
-	s64 min_value;
-	u64 max_value;
-	u32 min_align;
-	u32 aux_off;
-	u32 aux_off_align;
-	bool value_from_signed;
+	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 */
 };
 
 enum bpf_stack_slot_type {

include/linux/tnum.h

+/* tnum: tracked (or tristate) numbers
+ *
+ * A tnum tracks knowledge about the bits of a value.  Each bit can be either
+ * known (0 or 1), or unknown (x).  Arithmetic operations on tnums will
+ * propagate the unknown bits such that the tnum result represents all the
+ * possible results for possible values of the operands.
+ */
+#include <linux/types.h>
+
+struct tnum {
+	u64 value;
+	u64 mask;
+};
+
+/* Constructors */
+/* Represent a known constant as a tnum. */
+struct tnum tnum_const(u64 value);
+/* A completely unknown value */
+extern const struct tnum tnum_unknown;
+/* A value that's unknown except that @min <= value <= @max */
+struct tnum tnum_range(u64 min, u64 max);
+
+/* Arithmetic and logical ops */
+/* Shift a tnum left (by a fixed shift) */
+struct tnum tnum_lshift(struct tnum a, u8 shift);
+/* Shift a tnum right (by a fixed shift) */
+struct tnum tnum_rshift(struct tnum a, u8 shift);
+/* Add two tnums, return @a + @b */
+struct tnum tnum_add(struct tnum a, struct tnum b);
+/* Subtract two tnums, return @a - @b */
+struct tnum tnum_sub(struct tnum a, struct tnum b);
+/* Bitwise-AND, return @a & @b */
+struct tnum tnum_and(struct tnum a, struct tnum b);
+/* Bitwise-OR, return @a | @b */
+struct tnum tnum_or(struct tnum a, struct tnum b);
+/* Bitwise-XOR, return @a ^ @b */
+struct tnum tnum_xor(struct tnum a, struct tnum b);
+/* Multiply two tnums, return @a * @b */
+struct tnum tnum_mul(struct tnum a, struct tnum b);
+
+/* Return a tnum representing numbers satisfying both @a and @b */
+struct tnum tnum_intersect(struct tnum a, struct tnum b);
+
+/* Return @a with all but the lowest @size bytes cleared */
+struct tnum tnum_cast(struct tnum a, u8 size);
+
+/* Returns true if @a is a known constant */
+static inline bool tnum_is_const(struct tnum a)
+{
+	return !a.mask;
+}
+
+/* Returns true if @a == tnum_const(@b) */
+static inline bool tnum_equals_const(struct tnum a, u64 b)
+{
+	return tnum_is_const(a) && a.value == b;
+}
+
+/* Returns true if @a is completely unknown */
+static inline bool tnum_is_unknown(struct tnum a)
+{
+	return !~a.mask;
+}
+
+/* Returns true if @a is known to be a multiple of @size.
+ * @size must be a power of two.
+ */
+bool tnum_is_aligned(struct tnum a, u64 size);
+
+/* Returns true if @b represents a subset of @a. */
+bool tnum_in(struct tnum a, struct tnum b);
+
+/* Formatting functions.  These have snprintf-like semantics: they will write
+ * up to @size bytes (including the terminating NUL byte), and return the number
+ * of bytes (excluding the terminating NUL) which would have been written had
+ * sufficient space been available.  (Thus tnum_sbin always returns 64.)
+ */
+/* Format a tnum as a pair of hex numbers (value; mask) */
+int tnum_strn(char *str, size_t size, struct tnum a);
+/* Format a tnum as tristate binary expansion */
+int tnum_sbin(char *str, size_t size, struct tnum a);

kernel/bpf/Makefile

 obj-y := core.o
 
-obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o
+obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o
 obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o
 ifeq ($(CONFIG_NET),y)
 obj-$(CONFIG_BPF_SYSCALL) += devmap.o

kernel/bpf/tnum.c

+/* tnum: tracked (or tristate) numbers
+ *
+ * A tnum tracks knowledge about the bits of a value.  Each bit can be either
+ * known (0 or 1), or unknown (x).  Arithmetic operations on tnums will
+ * propagate the unknown bits such that the tnum result represents all the
+ * possible results for possible values of the operands.
+ */
+#include <linux/kernel.h>
+#include <linux/tnum.h>
+
+#define TNUM(_v, _m)	(struct tnum){.value = _v, .mask = _m}
+/* A completely unknown value */
+const struct tnum tnum_unknown = { .value = 0, .mask = -1 };
+
+struct tnum tnum_const(u64 value)
+{
+	return TNUM(value, 0);
+}
+
+struct tnum tnum_range(u64 min, u64 max)
+{
+	u64 chi = min ^ max, delta;
+	u8 bits = fls64(chi);
+
+	/* special case, needed because 1ULL << 64 is undefined */
+	if (bits > 63)
+		return tnum_unknown;
+	/* e.g. if chi = 4, bits = 3, delta = (1<<3) - 1 = 7.
+	 * if chi = 0, bits = 0, delta = (1<<0) - 1 = 0, so we return
+	 *  constant min (since min == max).
+	 */
+	delta = (1ULL << bits) - 1;
+	return TNUM(min & ~delta, delta);
+}
+
+struct tnum tnum_lshift(struct tnum a, u8 shift)
+{
+	return TNUM(a.value << shift, a.mask << shift);
+}
+
+struct tnum tnum_rshift(struct tnum a, u8 shift)
+{
+	return TNUM(a.value >> shift, a.mask >> shift);
+}
+
+struct tnum tnum_add(struct tnum a, struct tnum b)
+{
+	u64 sm, sv, sigma, chi, mu;
+
+	sm = a.mask + b.mask;
+	sv = a.value + b.value;
+	sigma = sm + sv;
+	chi = sigma ^ sv;
+	mu = chi | a.mask | b.mask;
+	return TNUM(sv & ~mu, mu);
+}
+
+struct tnum tnum_sub(struct tnum a, struct tnum b)
+{
+	u64 dv, alpha, beta, chi, mu;
+
+	dv = a.value - b.value;
+	alpha = dv + a.mask;
+	beta = dv - b.mask;
+	chi = alpha ^ beta;
+	mu = chi | a.mask | b.mask;
+	return TNUM(dv & ~mu, mu);
+}
+
+struct tnum tnum_and(struct tnum a, struct tnum b)
+{
+	u64 alpha, beta, v;
+
+	alpha = a.value | a.mask;
+	beta = b.value | b.mask;
+	v = a.value & b.value;
+	return TNUM(v, alpha & beta & ~v);
+}
+
+struct tnum tnum_or(struct tnum a, struct tnum b)
+{
+	u64 v, mu;
+
+	v = a.value | b.value;
+	mu = a.mask | b.mask;
+	return TNUM(v, mu & ~v);
+}
+
+struct tnum tnum_xor(struct tnum a, struct tnum b)
+{
+	u64 v, mu;
+
+	v = a.value ^ b.value;
+	mu = a.mask | b.mask;
+	return TNUM(v & ~mu, mu);
+}
+
+/* half-multiply add: acc += (unknown * mask * value).
+ * An intermediate step in the multiply algorithm.
+ */
+static struct tnum hma(struct tnum acc, u64 value, u64 mask)
+{
+	while (mask) {
+		if (mask & 1)
+			acc = tnum_add(acc, TNUM(0, value));
+		mask >>= 1;
+		value <<= 1;
+	}
+	return acc;
+}
+
+struct tnum tnum_mul(struct tnum a, struct tnum b)
+{
+	struct tnum acc;
+	u64 pi;
+
+	pi = a.value * b.value;
+	acc = hma(TNUM(pi, 0), a.mask, b.mask | b.value);
+	return hma(acc, b.mask, a.value);
+}
+
+/* Note that if a and b disagree - i.e. one has a 'known 1' where the other has
+ * a 'known 0' - this will return a 'known 1' for that bit.
+ */
+struct tnum tnum_intersect(struct tnum a, struct tnum b)
+{
+	u64 v, mu;
+
+	v = a.value | b.value;
+	mu = a.mask & b.mask;
+	return TNUM(v & ~mu, mu);
+}
+
+struct tnum tnum_cast(struct tnum a, u8 size)
+{
+	a.value &= (1ULL << (size * 8)) - 1;
+	a.mask &= (1ULL << (size * 8)) - 1;
+	return a;
+}
+
+bool tnum_is_aligned(struct tnum a, u64 size)
+{
+	if (!size)
+		return true;
+	return !((a.value | a.mask) & (size - 1));
+}
+
+bool tnum_in(struct tnum a, struct tnum b)
+{
+	if (b.mask & ~a.mask)
+		return false;
+	b.value &= ~a.mask;
+	return a.value == b.value;
+}
+
+int tnum_strn(char *str, size_t size, struct tnum a)
+{
+	return snprintf(str, size, "(%#llx; %#llx)", a.value, a.mask);
+}
+EXPORT_SYMBOL_GPL(tnum_strn);
+
+int tnum_sbin(char *str, size_t size, struct tnum a)
+{
+	size_t n;
+
+	for (n = 64; n; n--) {
+		if (n < size) {
+			if (a.mask & 1)
+				str[n - 1] = 'x';
+			else if (a.value & 1)
+				str[n - 1] = '1';
+			else
+				str[n - 1] = '0';
+		}
+		a.mask >>= 1;
+		a.value >>= 1;
+	}
+	str[min(size - 1, (size_t)64)] = 0;
+	return 64;
+}