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