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bpf/verifier: rework value tracking

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Unifies adjusted and unadjusted register value types (e.g. FRAME_POINTER is
 now just a PTR_TO_STACK with zero offset).
Tracks value alignment by means of tracking known & unknown bits.  This
 also replaces the 'reg->imm' (leading zero bits) calculations for (what
 were) UNKNOWN_VALUEs.
If pointer leaks are allowed, and adjust_ptr_min_max_vals returns -EACCES,
 treat the pointer as an unknown scalar and try again, because we might be
 able to conclude something about the result (e.g. pointer & 0x40 is either
 0 or 0x40).
Verifier hooks in the netronome/nfp driver were changed to match the new
 data structures.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Edward Cree
2017-08-07 15:26:19 +01:00
committed by David S. Miller
parent e1cb90f2b8
commit f1174f77b5
7 changed files with 1277 additions and 864 deletions
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34
include/linux/bpf.h
View File

@@ -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;

34
include/linux/bpf_verifier.h
View File

@@ -9,6 +9,7 @@
#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.
@@ -19,30 +20,37 @@
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 three 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;
};

79
include/linux/tnum.h Normal file
View File

@@ -0,0 +1,79 @@
/* 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;
/* 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);