Re: [RFC PATCH net-next 4/5] bpf/verifier: track signed and unsigned min/max values

Allows us to, sometimes, combine information from a signed check of one
 bound and an unsigned check of the other.
We now track the full range of possible values, rather than restricting
 ourselves to [0, 1<<30) and considering anything beyond that as
 unknown.  While this is probably not necessary, it makes the code more
 straightforward and symmetrical between signed and unsigned bounds.

Signed-off-by: Edward Cree <ecree-s/n/eUQHGBpZroRs9YW3xA@public.gmane.org>
---
 include/linux/bpf_verifier.h |  22 +-
 kernel/bpf/verifier.c        | 661 +++++++++++++++++++++++++------------------
 2 files changed, 395 insertions(+), 288 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index e341469..10a5944 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h

@@ -11,11 +11,15 @@
 #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;

@@ -38,7 +42,7 @@ struct bpf_reg_state {
 	 * PTR_TO_MAP_VALUE_OR_NULL, we have to NULL-check it _first_.
 	 */
 	u32 id;
-	/* These three fields must be last.  See states_equal() */
+	/* 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

@@ -51,8 +55,10 @@ struct bpf_reg_state {
 	 * These refer to the same value as align, not necessarily the actual
 	 * contents of the register.
 	 */
-	s64 min_value; /* minimum possible (s64)value */
-	u64 max_value; /* maximum possible (u64)value */
+	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 */