From: Jisheng Zhang <jszhang@kernel.org>
To: Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>, Guo Ren <guoren@kernel.org>
Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: [PATCH v3] riscv: fix race when vmap stack overflow
Date: Sun, 30 Oct 2022 20:45:17 +0800 [thread overview]
Message-ID: <20221030124517.2370-1-jszhang@kernel.org> (raw)
Currently, when detecting vmap stack overflow, riscv firstly switches
to the so called shadow stack, then use this shadow stack to call the
get_overflow_stack() to get the overflow stack. However, there's
a race here if two or more harts use the same shadow stack at the same
time.
To solve this race, we introduce spin_shadow_stack atomic var, which
will be swap between its own address and 0 in atomic way, when the
var is set, it means the shadow_stack is being used; when the var
is cleared, it means the shadow_stack isn't being used.
Fixes: 31da94c25aea ("riscv: add VMAP_STACK overflow detection")
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Suggested-by: Guo Ren <guoren@kernel.org>
---
Since v2:
- use REG_AMOSWAP
- add comment to the purpose of smp_store_release()
Since v1:
- use smp_store_release directly
- use unsigned int instead of atomic_t
arch/riscv/include/asm/asm.h | 1 +
arch/riscv/kernel/entry.S | 4 ++++
arch/riscv/kernel/traps.c | 9 +++++++++
3 files changed, 14 insertions(+)
diff --git a/arch/riscv/include/asm/asm.h b/arch/riscv/include/asm/asm.h
index 1b471ff73178..acf563072b8b 100644
--- a/arch/riscv/include/asm/asm.h
+++ b/arch/riscv/include/asm/asm.h
@@ -23,6 +23,7 @@
#define REG_L __REG_SEL(ld, lw)
#define REG_S __REG_SEL(sd, sw)
#define REG_SC __REG_SEL(sc.d, sc.w)
+#define REG_AMOSWAP __REG_SEL(amoswap.d, amoswap.w)
#define REG_ASM __REG_SEL(.dword, .word)
#define SZREG __REG_SEL(8, 4)
#define LGREG __REG_SEL(3, 2)
diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index b9eda3fcbd6d..ea6b78dac739 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -404,6 +404,10 @@ handle_syscall_trace_exit:
#ifdef CONFIG_VMAP_STACK
handle_kernel_stack_overflow:
+1: la sp, spin_shadow_stack
+ REG_AMOSWAP sp, sp, (sp)
+ bnez sp, 1b
+
la sp, shadow_stack
addi sp, sp, SHADOW_OVERFLOW_STACK_SIZE
diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index f3e96d60a2ff..dea47f329708 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -221,11 +221,20 @@ asmlinkage unsigned long get_overflow_stack(void)
OVERFLOW_STACK_SIZE;
}
+unsigned long spin_shadow_stack;
+
asmlinkage void handle_bad_stack(struct pt_regs *regs)
{
unsigned long tsk_stk = (unsigned long)current->stack;
unsigned long ovf_stk = (unsigned long)this_cpu_ptr(overflow_stack);
+ /*
+ * to ensure spin flag is set after the sp is used in entry.S:
+ * //load per-cpu overflow stack.
+ * REG_L sp, -8(sp)
+ */
+ smp_store_release(&spin_shadow_stack, 0);
+
console_verbose();
pr_emerg("Insufficient stack space to handle exception!\n");
--
2.37.2
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next reply other threads:[~2022-10-30 12:55 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-30 12:45 Jisheng Zhang [this message]
2022-10-30 13:23 ` [PATCH v3] riscv: fix race when vmap stack overflow Guo Ren
2022-11-23 15:23 ` Jisheng Zhang
2022-11-30 2:29 ` Palmer Dabbelt
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