Mailing List Archive

commit 4ff3635be2766d3019e4d2aa830792dd503cef88
Author: Roger Pau Monné <roger.pau@citrix.com>
AuthorDate: Tue Feb 13 17:57:38 2024 +0100
Commit: Andrew Cooper <andrew.cooper3@citrix.com>
CommitDate: Tue Mar 12 16:37:45 2024 +0000

percpu-rwlock: introduce support for blocking speculation into critical regions

Add direct calls to block_lock_speculation() where required in order to prevent
speculation into the lock protected critical regions. Also convert
_percpu_read_lock() from inline to always_inline.

Note that _percpu_write_lock() has been modified the use the non speculation
safe of the locking primites, as a speculation is added unconditionally by the
calling wrapper.

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 f218daf6d3a3b847736d37c6a6b76031a0d08441)
---
xen/common/rwlock.c | 6 +++++-
xen/include/xen/rwlock.h | 14 ++++++++++----
2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/xen/common/rwlock.c b/xen/common/rwlock.c
index 2464f74548..703276f4aa 100644
--- a/xen/common/rwlock.c
+++ b/xen/common/rwlock.c
@@ -125,8 +125,12 @@ void _percpu_write_lock(percpu_rwlock_t **per_cpudata,
/*
* First take the write lock to protect against other writers or slow
* path readers.
+ *
+ * Note we use the speculation unsafe variant of write_lock(), as the
+ * calling wrapper already adds a speculation barrier after the lock has
+ * been taken.
*/
- write_lock(&percpu_rwlock->rwlock);
+ _write_lock(&percpu_rwlock->rwlock);

/* Now set the global variable so that readers start using read_lock. */
percpu_rwlock->writer_activating = 1;
diff --git a/xen/include/xen/rwlock.h b/xen/include/xen/rwlock.h
index fd0458be94..abe0804bf7 100644
--- a/xen/include/xen/rwlock.h
+++ b/xen/include/xen/rwlock.h
@@ -326,8 +326,8 @@ static inline void _percpu_rwlock_owner_check(percpu_rwlock_t **per_cpudata,
#define percpu_rwlock_resource_init(l, owner) \
(*(l) = (percpu_rwlock_t)PERCPU_RW_LOCK_UNLOCKED(&get_per_cpu_var(owner)))

-static inline void _percpu_read_lock(percpu_rwlock_t **per_cpudata,
- percpu_rwlock_t *percpu_rwlock)
+static always_inline void _percpu_read_lock(percpu_rwlock_t **per_cpudata,
+ percpu_rwlock_t *percpu_rwlock)
{
/* Validate the correct per_cpudata variable has been provided. */
_percpu_rwlock_owner_check(per_cpudata, percpu_rwlock);
@@ -362,6 +362,8 @@ static inline void _percpu_read_lock(percpu_rwlock_t **per_cpudata,
}
else
{
+ /* Other branch already has a speculation barrier in read_lock(). */
+ block_lock_speculation();
/* All other paths have implicit check_lock() calls via read_lock(). */
check_lock(&percpu_rwlock->rwlock.lock.debug, false);
}
@@ -410,8 +412,12 @@ static inline void _percpu_write_unlock(percpu_rwlock_t **per_cpudata,
_percpu_read_lock(&get_per_cpu_var(percpu), lock)
#define percpu_read_unlock(percpu, lock) \
_percpu_read_unlock(&get_per_cpu_var(percpu), lock)
-#define percpu_write_lock(percpu, lock) \
- _percpu_write_lock(&get_per_cpu_var(percpu), lock)
+
+#define percpu_write_lock(percpu, lock) \
+({ \
+ _percpu_write_lock(&get_per_cpu_var(percpu), lock); \
+ block_lock_speculation(); \
+})
#define percpu_write_unlock(percpu, lock) \
_percpu_write_unlock(&get_per_cpu_var(percpu), lock)

--
generated by git-patchbot for /home/xen/git/xen.git#staging-4.15