Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 15 Sep 2022 11:48:22 -0700 (PDT)
Subject: Re: [PATCH] riscv: fix a nasty sigreturn bug...
In-Reply-To: <YxJEiSq/CGaL6Gm9@ZenIV>
CC:     Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org
From:   Palmer Dabbelt <palmer@dabbelt.com>
To:     viro@zeniv.linux.org.uk, ajones@ventanamicro.com
Message-ID: <mhng-d888fd65-86fc-4c2d-8a0f-801e9da62701@palmer-ri-x1c9>
Mime-Version: 1.0 (MHng)
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk

> Ping?  Does anybody have objections?  AFAICS, the bug is still
> there...

Sorry, something's gone off the rails with email and this thread doesn't 
show up in my inbox (not even any of the replies).  I tried to patch 
together this reply manually so hopefully it works.

This is on fixes, thanks -- trying to debug this one would have been a 
nightmare.

> On Fri, Sep 24, 2021 at 01:55:27AM +0000, Al Viro wrote:
>> riscv has an equivalent of arm bug fixed by 653d48b22166; if signal
>> gets caught by an interrupt that hits when we have the right value
>> in a0 (-513), *and* another signal gets delivered upon sigreturn()
>> (e.g. included into the blocked mask for the first signal and posted
>> while the handler had been running), the syscall restart logics will
>> see regs->cause equal to EXC_SYSCALL (we are in a syscall, after all)
>> and a0 already restored to its original value (-513, which happens to
>> be -ERESTARTNOINTR) and assume that we need to apply the usual
>> syscall restart logics.
>>     
>> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
>> ---
>> diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
>> index c2d5ecbe55264..f8fb85dc94b7a 100644
>> --- a/arch/riscv/kernel/signal.c
>> +++ b/arch/riscv/kernel/signal.c
>> @@ -121,6 +121,8 @@ SYSCALL_DEFINE0(rt_sigreturn)
>>  	if (restore_altstack(&frame->uc.uc_stack))
>>  		goto badframe;
>>  
>> +	regs->cause = -1UL;
>> +
>>  	return regs->a0;
>>  
>>  badframe: