From fb13b11d53875e28e7fbf0c26b288e4ea676aa9f Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Andr=C3=A9=20R=C3=B6sti?= Date: Mon, 11 Mar 2024 21:17:04 +0000 Subject: [PATCH] entry: Respect changes to system call number by trace_sys_enter() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20240311211704.7262-1-an.roesti@gmail.com --- kernel/entry/common.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/entry/common.c b/kernel/entry/common.c index 88cb3c88aaa5..90843cc38588 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -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);