[PATCH 5.15 140/690] entry: Respect changes to system call number by trace_sys_enter()

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5.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: André Rösti <an.roesti@xxxxxxxxx>

[ Upstream commit fb13b11d53875e28e7fbf0c26b288e4ea676aa9f ]

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@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240311211704.7262-1-an.roesti@xxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 e002bea6b4be3..d11d4047a0ca8 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -73,8 +73,14 @@ static 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);
 
-- 
2.43.0







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