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From:   Christophe Leroy <christophe.leroy@c-s.fr>
Subject: [RFC PATCH 5/8] powerpc/irq: move stack overflow verification
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Date:   Mon, 23 Dec 2019 15:26:15 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

As we are going to switch to IRQ stack immediately in the exception
handler, it won't be possible anymore to check stack overflow by
reading stack pointer.

Do the verification on regs->gpr[1] which contains the stack pointer
at the time the IRQ happended, and move it to __do_irq() so that the
verification is also done when calling __do_irq() directly once the
exception entry does the stack switch.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 arch/powerpc/kernel/irq.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 28414c6665cc..4df49f6e9987 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -596,15 +596,16 @@ u64 arch_irq_stat_cpu(unsigned int cpu)
 	return sum;
 }
 
-static inline void check_stack_overflow(void)
+static inline void check_stack_overflow(struct pt_regs *regs)
 {
 #ifdef CONFIG_DEBUG_STACKOVERFLOW
+	bool is_user = user_mode(regs);
 	long sp;
 
-	sp = current_stack_pointer() & (THREAD_SIZE-1);
+	sp = regs->gpr[1] & (THREAD_SIZE - 1);
 
 	/* check for stack overflow: is there less than 2KB free? */
-	if (unlikely(sp < 2048)) {
+	if (unlikely(!is_user && sp < 2048)) {
 		pr_err("do_IRQ: stack overflow: %ld\n", sp);
 		dump_stack();
 	}
@@ -654,6 +655,8 @@ void __do_irq(struct pt_regs *regs)
 
 	trace_irq_entry(regs);
 
+	check_stack_overflow(regs);
+
 	/*
 	 * Query the platform PIC for the interrupt & ack it.
 	 *
@@ -685,8 +688,6 @@ void do_IRQ(struct pt_regs *regs)
 	irqsp = hardirq_ctx[raw_smp_processor_id()];
 	sirqsp = softirq_ctx[raw_smp_processor_id()];
 
-	check_stack_overflow();
-
 	/* Already there ? Otherwise switch stack and call */
 	if (unlikely(cursp == irqsp || cursp == sirqsp))
 		__do_irq(regs);
-- 
2.13.3