From: Miguel Ojeda <ojeda@xxxxxxxxxx>
commit 6618d69aa129a8fc613e64775d5019524c6f231b upstream.
At the moment it is possible to perform unsafe operations in
the arguments of `pr_*` macros since they are evaluated inside
an `unsafe` block:
let x = &10u32 as *const u32;
pr_info!("{}", *x);
In other words, this is a soundness issue.
Fix it so that it requires an explicit `unsafe` block.
Reported-by: Wedson Almeida Filho <wedsonaf@xxxxxxxxx>
Reported-by: Domen Puncer Kugler <domen.puncerkugler@xxxxxxxxxxxx>
Link: https://github.com/Rust-for-Linux/linux/issues/479
Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
Reviewed-by: Boqun Feng <boqun.feng@xxxxxxxxx>
Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>
Reviewed-by: Björn Roy Baron <bjorn3_gh@xxxxxxxxxxxxxx>
Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
rust/kernel/print.rs | 29 ++++++++++++++++++-----------
1 file changed, 18 insertions(+), 11 deletions(-)
--- a/rust/kernel/print.rs
+++ b/rust/kernel/print.rs
@@ -115,17 +115,24 @@ pub unsafe fn call_printk(
macro_rules! print_macro (
// The non-continuation cases (most of them, e.g. `INFO`).
($format_string:path, $($arg:tt)+) => (
- // SAFETY: This hidden macro should only be called by the documented
- // printing macros which ensure the format string is one of the fixed
- // ones. All `__LOG_PREFIX`s are null-terminated as they are generated
- // by the `module!` proc macro or fixed values defined in a kernel
- // crate.
- unsafe {
- $crate::print::call_printk(
- &$format_string,
- crate::__LOG_PREFIX,
- format_args!($($arg)+),
- );
+ // To remain sound, `arg`s must be expanded outside the `unsafe` block.
+ // Typically one would use a `let` binding for that; however, `format_args!`
+ // takes borrows on the arguments, but does not extend the scope of temporaries.
+ // Therefore, a `match` expression is used to keep them around, since
+ // the scrutinee is kept until the end of the `match`.
+ match format_args!($($arg)+) {
+ // SAFETY: This hidden macro should only be called by the documented
+ // printing macros which ensure the format string is one of the fixed
+ // ones. All `__LOG_PREFIX`s are null-terminated as they are generated
+ // by the `module!` proc macro or fixed values defined in a kernel
+ // crate.
+ args => unsafe {
+ $crate::print::call_printk(
+ &$format_string,
+ crate::__LOG_PREFIX,
+ args,
+ );
+ }
}
);
);
