Commit fb13b11d authored by André Rösti's avatar André Rösti Committed by Thomas Gleixner
Browse files

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 b6ec4134 ("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: b6ec4134 ("core/entry: Report syscall correctly for trace and audit")
Signed-off-by: default avatarAndré Rösti <an.roesti@gmail.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240311211704.7262-1-an.roesti@gmail.com
parent e8f897f4

kernel/entry/common.c

+7 −1
Original line number Diff line number Diff line
@@ -57,8 +57,14 @@ long syscall_trace_enter(struct pt_regs *regs, long syscall, 
	/* 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);