linux-kernel - [PATCH] riscv: Fix SMP when shadow call stacks are enabled

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Message-ID: <20231121211958.3158576-1-samuel.holland@sifive.com>
Date:   Tue, 21 Nov 2023 13:19:29 -0800
From:   Samuel Holland <samuel.holland@...ive.com>
To:     Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv@...ts.infradead.org
Cc:     Samuel Holland <samuel.holland@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andy Chiu <andy.chiu@...ive.com>,
        Clément Léger <cleger@...osinc.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Greentime Hu <greentime.hu@...ive.com>,
        Guo Ren <guoren@...nel.org>, Heiko Stuebner <heiko@...ech.de>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nam Cao <namcaov@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] riscv: Fix SMP when shadow call stacks are enabled

This fixes two bugs in SCS initialization for secondary CPUs. First,
the SCS was not initialized at all in the spinwait boot path. Second,
the code for the SBI HSM path attempted to initialize the SCS before
enabling the MMU. However, that involves dereferencing the thread
pointer, which requires the MMU to be enabled.

Fix both issues by setting up the SCS in the common secondary entry
path, after enabling the MMU.

Fixes: d1584d791a29 ("riscv: Implement Shadow Call Stack")
Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
---

 arch/riscv/kernel/head.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index b77397432403..76ace1e0b46f 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -154,7 +154,6 @@ secondary_start_sbi:
 	XIP_FIXUP_OFFSET a3
 	add a3, a3, a1
 	REG_L sp, (a3)
-	scs_load_current
 
 .Lsecondary_start_common:
 
@@ -165,6 +164,7 @@ secondary_start_sbi:
 	call relocate_enable_mmu
 #endif
 	call .Lsetup_trap_vector
+	scs_load_current
 	tail smp_callin
 #endif /* CONFIG_SMP */
 
-- 
2.42.0