9cbe1f5a32
When helpers like bpf_get_stack returns an int value
and later on used for arithmetic computation, the LSH and ARSH
operations are often required to get proper sign extension into
64-bit. For example, without this patch:
54: R0=inv(id=0,umax_value=800)
54: (bf) r8 = r0
55: R0=inv(id=0,umax_value=800) R8_w=inv(id=0,umax_value=800)
55: (67) r8 <<= 32
56: R8_w=inv(id=0,umax_value=3435973836800,var_off=(0x0; 0x3ff00000000))
56: (c7) r8 s>>= 32
57: R8=inv(id=0)
With this patch:
54: R0=inv(id=0,umax_value=800)
54: (bf) r8 = r0
55: R0=inv(id=0,umax_value=800) R8_w=inv(id=0,umax_value=800)
55: (67) r8 <<= 32
56: R8_w=inv(id=0,umax_value=3435973836800,var_off=(0x0; 0x3ff00000000))
56: (c7) r8 s>>= 32
57: R8=inv(id=0, umax_value=800,var_off=(0x0; 0x3ff))
With better range of "R8", later on when "R8" is added to other register,
e.g., a map pointer or scalar-value register, the better register
range can be derived and verifier failure may be avoided.
In our later example,
......
usize = bpf_get_stack(ctx, raw_data, max_len, BPF_F_USER_STACK);
if (usize < 0)
return 0;
ksize = bpf_get_stack(ctx, raw_data + usize, max_len - usize, 0);
......
Without improving ARSH value range tracking, the register representing
"max_len - usize" will have smin_value equal to S64_MIN and will be
rejected by verifier.
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
83 lines
2.9 KiB
C
83 lines
2.9 KiB
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/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 (rsh) a tnum right (by a fixed shift) */
|
|
struct tnum tnum_rshift(struct tnum a, u8 shift);
|
|
/* Shift (arsh) a tnum right (by a fixed min_shift) */
|
|
struct tnum tnum_arshift(struct tnum a, u8 min_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);
|