From 836b2fe544a5e9b5ce116622cb36fba33838c6fd Mon Sep 17 00:00:00 2001
From: Eduard Zingerman <eddyz87@gmail.com>
Date: Fri, 4 Sep 2026 01:33:23 -0700
Subject: selftests/bpf: Check that JMP32 pointer vs zero jumps are not
 predicted

Add jmp32_ptr_vs_zero_jne: the fall-through of the 32-bit compare, which
the verifier used to skip, contains an out of bounds map value access,
hence w/o the previous patch the program is accepted. See previous patch
for detailed description.

Reported-by: Nicholas Carlini <npc@anthropic.com>
Suggested-by: Nicholas Carlini <npc@anthropic.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20260904083325.2083493-6-eddyz87@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 rust/syn/bigint.rs | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)
 create mode 100644 rust/syn/bigint.rs

(limited to 'rust/syn/bigint.rs')

diff --git a/rust/syn/bigint.rs b/rust/syn/bigint.rs
new file mode 100644
index 000000000..d706f9f51
--- /dev/null
+++ b/rust/syn/bigint.rs
@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+use std::ops::{AddAssign, MulAssign};
+
+// For implementing base10_digits() accessor on LitInt.
+pub(crate) struct BigInt {
+    digits: Vec<u8>,
+}
+
+impl BigInt {
+    pub(crate) fn new() -> Self {
+        BigInt { digits: Vec::new() }
+    }
+
+    pub(crate) fn to_string(&self) -> String {
+        let mut repr = String::with_capacity(self.digits.len());
+
+        let mut has_nonzero = false;
+        for digit in self.digits.iter().rev() {
+            has_nonzero |= *digit != 0;
+            if has_nonzero {
+                repr.push((*digit + b'0') as char);
+            }
+        }
+
+        if repr.is_empty() {
+            repr.push('0');
+        }
+
+        repr
+    }
+
+    fn reserve_two_digits(&mut self) {
+        let len = self.digits.len();
+        let desired =
+            len + !self.digits.ends_with(&[0, 0]) as usize + !self.digits.ends_with(&[0]) as usize;
+        self.digits.resize(desired, 0);
+    }
+}
+
+impl AddAssign<u8> for BigInt {
+    // Assumes increment <16.
+    fn add_assign(&mut self, mut increment: u8) {
+        self.reserve_two_digits();
+
+        let mut i = 0;
+        while increment > 0 {
+            let sum = self.digits[i] + increment;
+            self.digits[i] = sum % 10;
+            increment = sum / 10;
+            i += 1;
+        }
+    }
+}
+
+impl MulAssign<u8> for BigInt {
+    // Assumes base <=16.
+    fn mul_assign(&mut self, base: u8) {
+        self.reserve_two_digits();
+
+        let mut carry = 0;
+        for digit in &mut self.digits {
+            let prod = *digit * base + carry;
+            *digit = prod % 10;
+            carry = prod / 10;
+        }
+    }
+}
-- 
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