LoongArch: Fix access error when read fault on a write-only VMA

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

Posted by Huacai Chen 1 week, 4 days ago

From: Jiantao Shan <shanjiantao@loongson.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@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.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

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

Posted by Markus Elfring 1 week, 4 days ago

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

Will the tag “Fixes” become relevant here?

Regards,
Markus

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

Posted by Huacai Chen 1 week, 3 days ago

Hi, Markus,

On Tue, Apr 23, 2024 at 5:45 PM Markus Elfring <Markus.Elfring@web.de> wrote:
>
> > As with most architectures, allow handling of read faults in VMAs that
> > have VM_WRITE but without VM_READ (WRITE implies READ).
> …
>
> Will the tag “Fixes” become relevant here?
Yes, you are right, thank you.

Huacai
>
> Regards,
> Markus