linux-kernel - [PATCH] LoongArch: Fix access error when read fault on a write-only VMA

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Message-ID: <20240423074257.2480274-1-chenhuacai@loongson.cn>
Date: Tue, 23 Apr 2024 15:42:57 +0800
From: Huacai Chen <chenhuacai@...ngson.cn>
To: Arnd Bergmann <arnd@...db.de>,
	Huacai Chen <chenhuacai@...nel.org>
Cc: loongarch@...ts.linux.dev,
	linux-arch@...r.kernel.org,
	Xuefeng Li <lixuefeng@...ngson.cn>,
	Guo Ren <guoren@...nel.org>,
	Xuerui Wang <kernel@...0n.name>,
	Jiaxun Yang <jiaxun.yang@...goat.com>,
	linux-kernel@...r.kernel.org,
	loongson-kernel@...ts.loongnix.cn,
	Jiantao Shan <shanjiantao@...ngson.cn>,
	Huacai Chen <chenhuacai@...ngson.cn>
Subject: [PATCH] LoongArch: Fix access error when read fault on a write-only VMA

From: Jiantao Shan <shanjiantao@...ngson.cn>

As with most architectures, allow handling of read faults in VMAs that
have VM_WRITE but without VM_READ (WRITE implies READ).

Otherwise, reading before writing a write-only memory will error while
reading after writing everything is fine.

BTW, move the VM_EXEC judgement before VM_READ/VM_WRITE to make logic a
little clearer.

Signed-off-by: Jiantao Shan <shanjiantao@...ngson.cn>
Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
---
 arch/loongarch/mm/fault.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/loongarch/mm/fault.c b/arch/loongarch/mm/fault.c
index 1fc2f6813ea0..97b40defde06 100644
--- a/arch/loongarch/mm/fault.c
+++ b/arch/loongarch/mm/fault.c
@@ -202,10 +202,10 @@ static void __kprobes __do_page_fault(struct pt_regs *regs,
 		if (!(vma->vm_flags & VM_WRITE))
 			goto bad_area;
 	} else {
-		if (!(vma->vm_flags & VM_READ) && address != exception_era(regs))
-			goto bad_area;
 		if (!(vma->vm_flags & VM_EXEC) && address == exception_era(regs))
 			goto bad_area;
+		if (!(vma->vm_flags & (VM_READ | VM_WRITE)) && address != exception_era(regs))
+			goto bad_area;
 	}
 
 	/*
-- 
2.43.0