Received-SPF: pass (google.com: domain of linux-kernel+bounces-100260-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45d1:ec00::1 as permitted sender) client-ip=2604:1380:45d1:ec00::1;
Date: Tue, 12 Mar 2024 12:31:33 -0000
From:
 tip-bot2 for =?utf-8?q?Andr=C3=A9_R=C3=B6sti?= <tip-bot2@linutronix.de>
Sender: tip-bot2@linutronix.de
Reply-to: linux-kernel@vger.kernel.org
To: linux-tip-commits@vger.kernel.org
Subject: [tip: core/entry] entry: Respect changes to system call number by
 trace_sys_enter()
Cc: an.roesti@gmail.com, Thomas Gleixner <tglx@linutronix.de>, x86@kernel.org,
 linux-kernel@vger.kernel.org
In-Reply-To: <20240311211704.7262-1-an.roesti@gmail.com>
References: <20240311211704.7262-1-an.roesti@gmail.com>
Precedence: bulk
MIME-Version: 1.0
Message-ID: <171024669388.398.6202671416393382328.tip-bot2@tip-bot2>
Robot-ID: <tip-bot2@linutronix.de>
Robot-Unsubscribe:
 Contact <mailto:tglx@linutronix.de> to get blacklisted from these emails
Precedence: bulk
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: quoted-printable

The following commit has been merged into the core/entry branch of tip:

Commit-ID:     fb13b11d53875e28e7fbf0c26b288e4ea676aa9f
Gitweb:        https://git.kernel.org/tip/fb13b11d53875e28e7fbf0c26b288e4ea67=
6aa9f
Author:        Andr=C3=A9 R=C3=B6sti <an.roesti@gmail.com>
AuthorDate:    Mon, 11 Mar 2024 21:17:04=20
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Tue, 12 Mar 2024 13:23:32 +01:00

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().=20

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 audi=
t")
Signed-off-by: Andr=C3=A9 R=C3=B6sti <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
---
 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 88cb3c8..90843cc 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -57,8 +57,14 @@ long syscall_trace_enter(struct pt_regs *regs, long syscal=
l,
 	/* Either of the above might have changed the syscall number */
 	syscall =3D syscall_get_nr(current, regs);
=20
-	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 =3D syscall_get_nr(current, regs);
+	}
=20
 	syscall_enter_audit(regs, syscall);
=20