linux-kernel - [PATCH v6 01/14] riscv: prevent null-pointer dereference with sbi_remote_fence

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Message-Id: <20220209123800.269774-2-heiko@sntech.de>
Date:   Wed,  9 Feb 2022 13:37:47 +0100
From:   Heiko Stuebner <heiko@...ech.de>
To:     palmer@...belt.com, paul.walmsley@...ive.com, aou@...s.berkeley.edu
Cc:     linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, robh+dt@...nel.org, wefu@...hat.com,
        liush@...winnertech.com, guoren@...nel.org, atishp@...shpatra.org,
        anup@...infault.org, drew@...gleboard.org, hch@....de,
        arnd@...db.de, wens@...e.org, maxime@...no.tech,
        gfavor@...tanamicro.com, andrea.mondelli@...wei.com,
        behrensj@....edu, xinhaoqu@...wei.com, huffman@...ence.com,
        mick@....forth.gr, allen.baum@...erantotech.com,
        jscheid@...tanamicro.com, rtrauben@...il.com, samuel@...lland.org,
        cmuellner@...ux.com, philipp.tomsich@...ll.eu,
        Heiko Stuebner <heiko@...ech.de>
Subject: [PATCH v6 01/14] riscv: prevent null-pointer dereference with sbi_remote_fence_i

The callback used inside sbi_remote_fence_i is set at sbi probe time
to the needed variant. Before that it is a NULL pointer.

Some users like the flush_icache_*() functions suggest a generic
functionality, that doesn't depend on a specific boot-stage but
uses sbi_remote_fence_i as one option to flush other cpu cores.

So they definitly shouldn't run into null-pointer dereference
issues when called "too early" during boot.

So introduce an empty function to be the standard for the __sbi_rfence
function pointer until sbi_init has run.

Users of sbi_remote_fence_i will have separate code for the local
cpu and sbi_init() is called before other cpus are brought up.
So there are no other cpus present at the time when the issue
might happen.

Signed-off-by: Heiko Stuebner <heiko@...ech.de>
---
 arch/riscv/kernel/sbi.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
index f72527fcb347..c839acd668d3 100644
--- a/arch/riscv/kernel/sbi.c
+++ b/arch/riscv/kernel/sbi.c
@@ -15,11 +15,19 @@
 unsigned long sbi_spec_version __ro_after_init = SBI_SPEC_VERSION_DEFAULT;
 EXPORT_SYMBOL(sbi_spec_version);
 
+static int __sbi_rfence_none(int fid, const struct cpumask *cpu_mask,
+			     unsigned long start, unsigned long size,
+			     unsigned long arg4, unsigned long arg5)
+{
+	return -EOPNOTSUPP;
+}
+
 static void (*__sbi_set_timer)(uint64_t stime) __ro_after_init;
 static int (*__sbi_send_ipi)(const struct cpumask *cpu_mask) __ro_after_init;
 static int (*__sbi_rfence)(int fid, const struct cpumask *cpu_mask,
 			   unsigned long start, unsigned long size,
-			   unsigned long arg4, unsigned long arg5) __ro_after_init;
+			   unsigned long arg4, unsigned long arg5)
+			   __ro_after_init = __sbi_rfence_none;
 
 struct sbiret sbi_ecall(int ext, int fid, unsigned long arg0,
 			unsigned long arg1, unsigned long arg2,
-- 
2.30.2