bpf: replace min/max fields with struct cnum{32,64}

Replace eight independent s64, u64, s32, u32 min/max fields in
bpf_reg_state with two circular number fields:
- cnum64 for a unified signed/unsigned 64-bit range tracking;
- cnum32 for a unified signed/unsigned 32-bit range tracking.
Each cnum represents a range as a single arc on the circular number
line (base + size), from which signed and unsigned bounds are derived
on demand via accessor functions introduced in the preceding commit.

Notable changes:
- Signed<->unsigned deductions in __reg_deduce_bounds() are removed.
- 64<->32 bit deductions are replaced with:
  - reg->r32 = cnum32_intersect(reg->r32, cnum32_from_cnum64(reg->r64));
    this is functionally equivalent to the old code.
  - reg->r64 = cnum64_cnum32_intersect(reg->r64, reg->r32);
    this handles a few additional cases, see commit message for
    "bpf: representation and basic operations on circular numbers".
- regs_refine_cond_op() now computes results in terms of operations on
  sets, e.g. for JNE:

    /* Complement of the range [val, val] as cnum64. */
    lo = (struct cnum64){ val + 1, U64_MAX - 1 };
    reg1->r64 = cnum64_intersect(reg1->r64, lo);

- For add, sub operations on scalars replace explicit bounds
  computations with cnum{32,64}_{add,negate}.
- For add, sub operations on pointers deduplicate with arithmetic
  operations on scalars and use cnum{32,64}_{add,negate}.
- For and, or, xor operations on scalars remove explicit signed bounds
  computations.
- range_bounds_violation() reduces to checking cnum_is_empty().
- const_tnum_range_mismatch() reduces to checking cnum_is_const().

Selftest adjustments: a few existing tests are updated because a
single cnum arc cannot always represent what the old system expressed
as the intersection of independent signed and unsigned ranges.
For example, if the old system tracked u64=[0, U64_MAX-U32_MAX+2] and
s64=[S64_MIN+2, 2] independently, their intersection is a tight
two-point set. A single cnum must pick the shorter arc, losing the
other constraint. These cases are documented with comments in the
adjusted tests.

reg_bounds.c is updated with logic similar to
cnum64_cnum32_intersect(). Instead of using cnums it inspects
intersection between 'b' and first / last / next-after-first /
previous-before-last sub-ranges of 'a'.

reg_bounds.c is also updated to skip test cases that rely
in signed and unsigned ranges intersecting in two intervals,
as such cases are not representable by a single cnum.
The following "crafted" test cases are affected:
- reg_bounds_crafted/(s64)[0xffffffffffff8000; 0x7fff] (u32)<op> [0; 0x1f]
- reg_bounds_crafted/(s64)[0; 0x1f] (u32)<op> [0xffffffffffffff80; 0x7f]
- reg_bounds_crafted/(s64)[0xffffffffffffff80; 0x7f] (u32)<op> [0; 0x1f]
- reg_bounds_crafted/(u64)[0; 1] (s32)<op> [1; 2147483648]
- reg_bounds_crafted/(u64)[1; 2147483648] (s32)<op> [0; 1]
- reg_bounds_crafted/(u64)[0; 0xffffffff00000000] (s64)<op> 0
- reg_bounds_crafted/(u64)0 (s64)<op> [0; 0xffffffff00000000]
- reg_bounds_crafted/(u64)[0; 0xffffffff00000000] (s32)<op> 0
- reg_bounds_crafted/(u64)0 (s32)<op> [0; 0xffffffff00000000]
- reg_bounds_crafted/(s64)[S64_MIN; 0] (u64)<op> S64_MIN
- reg_bounds_crafted/(s64)S64_MIN (u64)<op> [S64_MIN; 0]
- reg_bounds_crafted/(s32)[S32_MIN; 0] (u32)<op> S32_MIN
- reg_bounds_crafted/(s32)S32_MIN (u32)<op> [S32_MIN; 0]
- reg_bounds_crafted/(s64)[0; 0x1f] (u32)<op> [0xffffffff80000000; 0x7fffffff]
- reg_bounds_crafted/(s64)[0xffffffff80000000; 0x7fffffff] (u32)<op> [0; 0x1f]
- reg_bounds_crafted/(s64)[0; 0x1f] (u32)<op> [0xffffffffffff8000; 0x7fff]

As well as some reg_bounds_roand_{consts,ranges}_A_B, where A and B
differ in sign domain.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260424-cnums-everywhere-rfc-v1-v3-3-ca434b39a486@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 15 insertions, 24 deletions

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index bf3ffa56bbe5..101ca6cc5424 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -8,6 +8,7 @@
 #include <linux/btf.h> /* for struct btf and btf_id() */
 #include <linux/filter.h> /* for MAX_BPF_STACK */
 #include <linux/tnum.h>
+#include <linux/cnum.h>
 
 /* Maximum variable offset umax_value permitted when resolving memory accesses.
  * In practice this is far bigger than any realistic pointer offset; this limit
@@ -120,14 +121,8 @@ struct bpf_reg_state {
 	 * 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 */
+	struct cnum64 r64; /* 64-bit range as circular number */
+	struct cnum32 r32; /* 32-bit range as circular number */
 	/* 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
@@ -211,66 +206,62 @@ struct bpf_reg_state {
 
 static inline s64 reg_smin(const struct bpf_reg_state *reg)
 {
-	return reg->smin_value;
+	return cnum64_smin(reg->r64);
 }
 
 static inline s64 reg_smax(const struct bpf_reg_state *reg)
 {
-	return reg->smax_value;
+	return cnum64_smax(reg->r64);
 }
 
 static inline u64 reg_umin(const struct bpf_reg_state *reg)
 {
-	return reg->umin_value;
+	return cnum64_umin(reg->r64);
 }
 
 static inline u64 reg_umax(const struct bpf_reg_state *reg)
 {
-	return reg->umax_value;
+	return cnum64_umax(reg->r64);
 }
 
 static inline s32 reg_s32_min(const struct bpf_reg_state *reg)
 {
-	return reg->s32_min_value;
+	return cnum32_smin(reg->r32);
 }
 
 static inline s32 reg_s32_max(const struct bpf_reg_state *reg)
 {
-	return reg->s32_max_value;
+	return cnum32_smax(reg->r32);
 }
 
 static inline u32 reg_u32_min(const struct bpf_reg_state *reg)
 {
-	return reg->u32_min_value;
+	return cnum32_umin(reg->r32);
 }
 
 static inline u32 reg_u32_max(const struct bpf_reg_state *reg)
 {
-	return reg->u32_max_value;
+	return cnum32_umax(reg->r32);
 }
 
 static inline void reg_set_srange32(struct bpf_reg_state *reg, s32 smin, s32 smax)
 {
-	reg->s32_min_value = smin;
-	reg->s32_max_value = smax;
+	reg->r32 = cnum32_from_srange(smin, smax);
 }
 
 static inline void reg_set_urange32(struct bpf_reg_state *reg, u32 umin, u32 umax)
 {
-	reg->u32_min_value = umin;
-	reg->u32_max_value = umax;
+	reg->r32 = cnum32_from_urange(umin, umax);
 }
 
 static inline void reg_set_srange64(struct bpf_reg_state *reg, s64 smin, s64 smax)
 {
-	reg->smin_value = smin;
-	reg->smax_value = smax;
+	reg->r64 = cnum64_from_srange(smin, smax);
 }
 
 static inline void reg_set_urange64(struct bpf_reg_state *reg, u64 umin, u64 umax)
 {
-	reg->umin_value = umin;
-	reg->umax_value = umax;
+	reg->r64 = cnum64_from_urange(umin, umax);
 }
 
 enum bpf_stack_slot_type {