From 33a154a96e71a34a1bcca9f40da343dbbf7b38b4 Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Thu, 1 Oct 2026 14:52:55 +0000 Subject: selftests/bpf: Test packet range of pointers sharing an id Add tests where two packet pointers share an id and tightening one pointer's umax from its var_off would put it less than their constant distance from the other's umax: with an index & 0x38 capped at 50, the base pointer keeps umax 50, so the pointer 8 bytes further on must keep umax 58, even though its known bits allow at most 56. These refused a valid program or accepted an out-of-bounds access before the fix: - check the advanced copy, load through the base: valid, was refused; - check the base, load the byte at base + 1 through a copy advanced by 8: was accepted; - check base + 4, load 4 bytes at base + 2 through base + 8: reads two bytes past the checked range, was accepted; - the same as the second with data_meta pointers checked against data: was accepted. These pass with and without the fix and cover nearby paths: - subtract an unknown scalar from a checked pointer and load below it (the range is kept across a new id); - reach a load through two paths whose checks cover 8 and 7 bytes after the loaded pointer; the second path must not be pruned by the first; - spill a copy of a pointer, check the pointer, fill the copy and load one byte past the checked range: the load is refused, and the copy has the range of the check. Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/bpf/20261001145255.855630-2-alexei.starovoitov@gmail.com Signed-off-by: Kumar Kartikeya Dwivedi --- rust/syn/thread.rs | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 62 insertions(+) create mode 100644 rust/syn/thread.rs (limited to 'rust/syn/thread.rs') diff --git a/rust/syn/thread.rs b/rust/syn/thread.rs new file mode 100644 index 000000000..4165a173d --- /dev/null +++ b/rust/syn/thread.rs @@ -0,0 +1,62 @@ +// SPDX-License-Identifier: Apache-2.0 OR MIT + +use std::fmt::{self, Debug}; +use std::thread::{self, ThreadId}; + +/// ThreadBound is a Sync-maker and Send-maker that allows accessing a value +/// of type T only from the original thread on which the ThreadBound was +/// constructed. +pub(crate) struct ThreadBound { + value: T, + thread_id: ThreadId, +} + +unsafe impl Sync for ThreadBound {} + +// Send bound requires Copy, as otherwise Drop could run in the wrong place. +// +// Today Copy and Drop are mutually exclusive so `T: Copy` implies `T: !Drop`. +// This impl needs to be revisited if that restriction is relaxed in the future. +unsafe impl Send for ThreadBound {} + +impl ThreadBound { + pub(crate) fn new(value: T) -> Self { + ThreadBound { + value, + thread_id: thread::current().id(), + } + } + + pub(crate) fn get(&self) -> Option<&T> { + if thread::current().id() == self.thread_id { + Some(&self.value) + } else { + None + } + } +} + +impl Debug for ThreadBound { + fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { + match self.get() { + Some(value) => Debug::fmt(value, formatter), + None => formatter.write_str("unknown"), + } + } +} + +// Copy the bytes of T, even if the currently running thread is the "wrong" +// thread. This is fine as long as the original thread is not simultaneously +// mutating this value via interior mutability, which would be a data race. +// +// Currently `T: Copy` is sufficient to guarantee that T contains no interior +// mutability, because _all_ interior mutability in Rust is built on +// std::cell::UnsafeCell, which has no Copy impl. This impl needs to be +// revisited if that restriction is relaxed in the future. +impl Copy for ThreadBound {} + +impl Clone for ThreadBound { + fn clone(&self) -> Self { + *self + } +} -- cgit v1.3.1