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commit 05b47a40c0e1522e9d7f52969c5936e39e163fb6
Author: Roger Pau Monné <roger.pau@citrix.com>
AuthorDate: Tue Feb 13 16:08:52 2024 +0100
Commit: Andrew Cooper <andrew.cooper3@citrix.com>
CommitDate: Tue Mar 12 16:37:45 2024 +0000

rwlock: introduce support for blocking speculation into critical regions

Introduce inline wrappers as required and add direct calls to
block_lock_speculation() in order to prevent speculation into the rwlock
protected critical regions.

Note the rwlock primitives are adjusted to use the non speculation safe variants
of the spinlock handlers, as a speculation barrier is added in the rwlock
calling wrappers.

trylock variants are protected by using lock_evaluate_nospec().

This is part of XSA-453 / CVE-2024-2193

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
(cherry picked from commit a1fb15f61692b1fa9945fc51f55471ace49cdd59)
---
xen/common/rwlock.c | 14 +++++++++++---
xen/include/xen/rwlock.h | 34 ++++++++++++++++++++++++++++------
2 files changed, 39 insertions(+), 9 deletions(-)

diff --git a/xen/common/rwlock.c b/xen/common/rwlock.c
index dadab372b5..2464f74548 100644
--- a/xen/common/rwlock.c
+++ b/xen/common/rwlock.c
@@ -34,8 +34,11 @@ void queue_read_lock_slowpath(rwlock_t *lock)

/*
* Put the reader into the wait queue.
+ *
+ * Use the speculation unsafe helper, as it's the caller responsibility to
+ * issue a speculation barrier if required.
*/
- spin_lock(&lock->lock);
+ _spin_lock(&lock->lock);

/*
* At the head of the wait queue now, wait until the writer state
@@ -64,8 +67,13 @@ void queue_write_lock_slowpath(rwlock_t *lock)
{
u32 cnts;

- /* Put the writer into the wait queue. */
- spin_lock(&lock->lock);
+ /*
+ * Put the writer into the wait queue.
+ *
+ * Use the speculation unsafe helper, as it's the caller responsibility to
+ * issue a speculation barrier if required.
+ */
+ _spin_lock(&lock->lock);

/* Try to acquire the lock directly if no reader is present. */
if ( !atomic_read(&lock->cnts) &&
diff --git a/xen/include/xen/rwlock.h b/xen/include/xen/rwlock.h
index 0cc9167715..fd0458be94 100644
--- a/xen/include/xen/rwlock.h
+++ b/xen/include/xen/rwlock.h
@@ -247,27 +247,49 @@ static inline int _rw_is_write_locked(rwlock_t *lock)
return (atomic_read(&lock->cnts) & _QW_WMASK) == _QW_LOCKED;
}

-#define read_lock(l) _read_lock(l)
-#define read_lock_irq(l) _read_lock_irq(l)
+static always_inline void read_lock(rwlock_t *l)
+{
+ _read_lock(l);
+ block_lock_speculation();
+}
+
+static always_inline void read_lock_irq(rwlock_t *l)
+{
+ _read_lock_irq(l);
+ block_lock_speculation();
+}
+
#define read_lock_irqsave(l, f) \
({ \
BUILD_BUG_ON(sizeof(f) != sizeof(unsigned long)); \
((f) = _read_lock_irqsave(l)); \
+ block_lock_speculation(); \
})

#define read_unlock(l) _read_unlock(l)
#define read_unlock_irq(l) _read_unlock_irq(l)
#define read_unlock_irqrestore(l, f) _read_unlock_irqrestore(l, f)
-#define read_trylock(l) _read_trylock(l)
+#define read_trylock(l) lock_evaluate_nospec(_read_trylock(l))
+
+static always_inline void write_lock(rwlock_t *l)
+{
+ _write_lock(l);
+ block_lock_speculation();
+}
+
+static always_inline void write_lock_irq(rwlock_t *l)
+{
+ _write_lock_irq(l);
+ block_lock_speculation();
+}

-#define write_lock(l) _write_lock(l)
-#define write_lock_irq(l) _write_lock_irq(l)
#define write_lock_irqsave(l, f) \
({ \
BUILD_BUG_ON(sizeof(f) != sizeof(unsigned long)); \
((f) = _write_lock_irqsave(l)); \
+ block_lock_speculation(); \
})
-#define write_trylock(l) _write_trylock(l)
+#define write_trylock(l) lock_evaluate_nospec(_write_trylock(l))

#define write_unlock(l) _write_unlock(l)
#define write_unlock_irq(l) _write_unlock_irq(l)
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.15