As Kees haved accepted the v2 patch at a381b70a1 which just
replaced rmb() with smp_rmb(), this patch will base on that and just adjust
the smp_rmb() to the correct position.
As the original comment shown (and indeed it should be):
/*
* Make sure that any changes to mode from another thread have
* been seen after SYSCALL_WORK_SECCOMP was seen.
*/
the smp_rmb() should be put between reading SYSCALL_WORK_SECCOMP and reading
seccomp.mode to make sure that any changes to mode from another thread have
been seen after SYSCALL_WORK_SECCOMP was seen, for TSYNC situation. However,
it is misplaced between reading seccomp.mode and seccomp->filter. This issue
seems to be misintroduced at 13aa72f0fd0a9f98a41cefb662487269e2f1ad65 which
aims to refactor the filter callback and the API. So let's just adjust the
smp_rmb() to the correct position.
A next optimization patch will be provided if this ajustment is appropriate.
v2 -> v3:
- move the smp_rmb() to the correct position
v1 -> v2:
- only replace rmb() with smp_rmb()
- provide the performance test number
RFC -> v1:
- replace rmb() with smp_rmb()
- move the smp_rmb() logic to the middle between TIF_SECCOMP and mode
Signed-off-by: wanghongzhe <wanghongzhe@xxxxxxxxxx>
---
kernel/seccomp.c | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 1d60fc2c9987..64b236cb8a7f 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -1160,12 +1160,6 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
int data;
struct seccomp_data sd_local;
- /*
- * Make sure that any changes to mode from another thread have
- * been seen after SYSCALL_WORK_SECCOMP was seen.
- */
- smp_rmb();
-
if (!sd) {
populate_seccomp_data(&sd_local);
sd = &sd_local;
@@ -1291,7 +1285,6 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
int __secure_computing(const struct seccomp_data *sd)
{
- int mode = current->seccomp.mode;
int this_syscall;
if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) &&
@@ -1301,7 +1294,13 @@ int __secure_computing(const struct seccomp_data *sd)
this_syscall = sd ? sd->nr :
syscall_get_nr(current, current_pt_regs());
- switch (mode) {
+ /*
+ * Make sure that any changes to mode from another thread have
+ * been seen after SYSCALL_WORK_SECCOMP was seen.
+ */
+ smp_rmb();
+
+ switch (current->seccomp.mode) {
case SECCOMP_MODE_STRICT:
__secure_computing_strict(this_syscall); /* may call do_exit */
return 0;
--
2.19.1
