linux-kernel - Re: [PATCH v2 0/3] Handle delay slot for extable lookup

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Date: Sat, 3 Feb 2024 13:56:43 +0000
From: Jiaxun Yang <jiaxun.yang@...goat.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>,
 Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Ben Hutchings <ben@...adent.org.uk>, linux-arch@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
 linux-mm@...ck.org, Xi Ruoyao <xry111@...111.site>
Subject: Re: [PATCH v2 0/3] Handle delay slot for extable lookup



在 2024/2/2 18:39, Linus Torvalds 写道:
> On Fri, 2 Feb 2024 at 04:30, Jiaxun Yang <jiaxun.yang@...goat.com> wrote:
>>        ptrace: Introduce exception_ip arch hook
>>        MIPS: Clear Cause.BD in instruction_pointer_set
>>        mm/memory: Use exception ip to search exception tables
> Just to clarify: does that second patch fix the problem that
> __isa_exception_epc() does a __get_user()?
>
> Because that mm/memory.c use of "exception_ip()" most definitely
> cannot take a page fault.

I reconsidered this issue today and I believe that exception_ip() usage 
here won't trigger
page_fault anyway.

Given that exception_ip is guarded by !user_mode(regs), EPC must points 
to a kernel
text address. There is no way accessing kernel text will generate such 
exception..

Thanks
>
> So if MIPS cannot do that whole exception IP thing without potentially
> touching user space, I do worry that we might just have to add a
>
>     #ifndef __MIPS__
>
> around this all.
>
> Possibly somehow limited to just the microMIPS/MIPS16e case in Kconfig instead?
>
>              Linus

-- 
---
Jiaxun Yang