linux-kernel - [patch V3 20/37] rseq: Replace the original debug implementation

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Message-ID: <20250904185720.403484967@linutronix.de>
Date: Fri,  5 Sep 2025 00:21:11 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Michael Jeanson <mjeanson@...icios.com>,
 Jens Axboe <axboe@...nel.dk>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Peter Zijlstra <peterz@...radead.org>,
 "Paul E. McKenney" <paulmck@...nel.org>,
 Boqun Feng <boqun.feng@...il.com>,
 Paolo Bonzini <pbonzini@...hat.com>,
 Sean Christopherson <seanjc@...gle.com>,
 Wei Liu <wei.liu@...nel.org>,
 Dexuan Cui <decui@...rosoft.com>,
 x86@...nel.org,
 Arnd Bergmann <arnd@...db.de>,
 Heiko Carstens <hca@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>,
 Huacai Chen <chenhuacai@...nel.org>,
 Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>
Subject: [patch V3 20/37] rseq: Replace the original debug implementation

Just utilize the new infrastructure and put the original one to rest.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

---
 kernel/rseq.c |   80 ++++++++--------------------------------------------------
 1 file changed, 12 insertions(+), 68 deletions(-)

--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -472,83 +472,27 @@ void __rseq_handle_notify_resume(struct
 
 #ifdef CONFIG_DEBUG_RSEQ
 /*
- * Unsigned comparison will be true when ip >= start_ip, and when
- * ip < start_ip + post_commit_offset.
- */
-static bool in_rseq_cs(unsigned long ip, struct rseq_cs *rseq_cs)
-{
-	return ip - rseq_cs->start_ip < rseq_cs->post_commit_offset;
-}
-
-/*
- * If the rseq_cs field of 'struct rseq' contains a valid pointer to
- * user-space, copy 'struct rseq_cs' from user-space and validate its fields.
- */
-static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)
-{
-	struct rseq_cs __user *urseq_cs;
-	u64 ptr;
-	u32 __user *usig;
-	u32 sig;
-	int ret;
-
-	if (get_user_masked_u64(&ptr, &t->rseq->rseq_cs))
-		return -EFAULT;
-
-	/* If the rseq_cs pointer is NULL, return a cleared struct rseq_cs. */
-	if (!ptr) {
-		memset(rseq_cs, 0, sizeof(*rseq_cs));
-		return 0;
-	}
-	/* Check that the pointer value fits in the user-space process space. */
-	if (ptr >= TASK_SIZE)
-		return -EINVAL;
-	urseq_cs = (struct rseq_cs __user *)(unsigned long)ptr;
-	if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs)))
-		return -EFAULT;
-
-	if (rseq_cs->start_ip >= TASK_SIZE ||
-	    rseq_cs->start_ip + rseq_cs->post_commit_offset >= TASK_SIZE ||
-	    rseq_cs->abort_ip >= TASK_SIZE ||
-	    rseq_cs->version > 0)
-		return -EINVAL;
-	/* Check for overflow. */
-	if (rseq_cs->start_ip + rseq_cs->post_commit_offset < rseq_cs->start_ip)
-		return -EINVAL;
-	/* Ensure that abort_ip is not in the critical section. */
-	if (rseq_cs->abort_ip - rseq_cs->start_ip < rseq_cs->post_commit_offset)
-		return -EINVAL;
-
-	usig = (u32 __user *)(unsigned long)(rseq_cs->abort_ip - sizeof(u32));
-	ret = get_user(sig, usig);
-	if (ret)
-		return ret;
-
-	if (current->rseq_sig != sig) {
-		printk_ratelimited(KERN_WARNING
-			"Possible attack attempt. Unexpected rseq signature 0x%x, expecting 0x%x (pid=%d, addr=%p).\n",
-			sig, current->rseq_sig, current->pid, usig);
-		return -EINVAL;
-	}
-	return 0;
-}
-
-/*
  * Terminate the process if a syscall is issued within a restartable
  * sequence.
  */
 void rseq_syscall(struct pt_regs *regs)
 {
-	unsigned long ip = instruction_pointer(regs);
 	struct task_struct *t = current;
-	struct rseq_cs rseq_cs;
+	u64 csaddr;
 
-	if (!t->rseq)
+	if (!t->rseq_event.has_rseq)
+		return;
+	if (get_user_masked_u64(&csaddr, &t->rseq->rseq_cs))
+		goto fail;
+	if (likely(!csaddr))
 		return;
-	if (rseq_get_rseq_cs(t, &rseq_cs) || in_rseq_cs(ip, &rseq_cs))
-		force_sig(SIGSEGV);
+	if (unlikely(csaddr >= TASK_SIZE))
+		goto fail;
+	if (rseq_debug_update_user_cs(t, regs, csaddr))
+		return;
+fail:
+	force_sig(SIGSEGV);
 }
-
 #endif
 
 /*