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entry: Respect changes to system call number by trace_sys_enter()

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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 b6ec413461 ("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: b6ec413461 ("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
This commit is contained in:
André Rösti 2024-03-11 21:17:04 +00:00 committed by Thomas Gleixner
parent e8f897f4af
commit fb13b11d53
1 changed files with 7 additions and 1 deletions
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8
kernel/entry/common.c
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@ -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);