entry: Respect changes to system call number by trace_sys_enter()
When a probe is registered at the trace_sys_enter() tracepoint, and that
probe changes the system call number, the old system call still gets
executed. This worked correctly until commit b6ec41346103 ("core/entry:
Report syscall correctly for trace and audit"), which removed the
re-evaluation of the syscall number after the trace point.
Restore the original semantics by re-evaluating the system call number
after trace_sys_enter().
The performance impact of this re-evaluation is minimal because it only
takes place when a trace point is active, and compared to the actual trace
point overhead the read from a cache hot variable is negligible.
Fixes: b6ec41346103 ("core/entry: Report syscall correctly for trace and audit")
Signed-off-by: André Rösti <an.roesti@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240311211704.7262-1-an.roesti@gmail.com
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 88cb3c8..90843cc3 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -57,8 +57,14 @@
/* Either of the above might have changed the syscall number */
syscall = syscall_get_nr(current, regs);
- if (unlikely(work & SYSCALL_WORK_SYSCALL_TRACEPOINT))
+ if (unlikely(work & SYSCALL_WORK_SYSCALL_TRACEPOINT)) {
trace_sys_enter(regs, syscall);
+ /*
+ * Probes or BPF hooks in the tracepoint may have changed the
+ * system call number as well.
+ */
+ syscall = syscall_get_nr(current, regs);
+ }
syscall_enter_audit(regs, syscall);
