linux-kernel - Re: [PATCH v2 5/5] powerpc/signal: Use unsafe_copy_siginfo_to

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Message-ID: <08117c1e-7805-534f-42ca-54a885f272cd@csgroup.eu>
Date:   Fri, 3 Sep 2021 10:53:49 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 5/5] powerpc/signal: Use unsafe_copy_siginfo_to_user()



Le 02/09/2021 à 20:38, Eric W. Biederman a écrit :
> Christophe Leroy <christophe.leroy@...roup.eu> writes:
> 
>> Use unsafe_copy_siginfo_to_user() in order to do the copy
>> within the user access block.
>>
>> On an mpc 8321 (book3s/32) the improvment is about 5% on a process
>> sending a signal to itself.
> 
> Nacked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> 
> copy_siginfo_to_user is not the same as copy_siginfo_to_user32.
> 
> As in this patch breaks 32bit userspace on powerpc.

I don't understand your comment. As you can see below, copy_siginfo_to_user32() is used in the 
compat case (ie 32 bit userspace on PPC64) and unsafe_copy_siginfo_to_user() is used on the 
non-compat case (ie 32 bit userspace on PPC32).

So what's the issue really ?

> 
> 
>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
>> ---
>>   arch/powerpc/kernel/signal_32.c | 13 ++++++-------
>>   arch/powerpc/kernel/signal_64.c |  5 +----
>>   2 files changed, 7 insertions(+), 11 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
>> index ff101e2b3bab..f9e16d108bc8 100644
>> --- a/arch/powerpc/kernel/signal_32.c
>> +++ b/arch/powerpc/kernel/signal_32.c
>> @@ -710,12 +710,6 @@ static long restore_tm_user_regs(struct pt_regs *regs, struct mcontext __user *s
>>   }
>>   #endif
>>   
>> -#ifdef CONFIG_PPC64
>> -
>> -#define copy_siginfo_to_user	copy_siginfo_to_user32
>> -
>> -#endif /* CONFIG_PPC64 */
>> -
>>   /*
>>    * Set up a signal frame for a "real-time" signal handler
>>    * (one which gets siginfo).
>> @@ -779,14 +773,19 @@ int handle_rt_signal32(struct ksignal *ksig, sigset_t *oldset,
>>   		asm("dcbst %y0; sync; icbi %y0; sync" :: "Z" (mctx->mc_pad[0]));
>>   	}
>>   	unsafe_put_sigset_t(&frame->uc.uc_sigmask, oldset, failed);
>> +#ifndef CONFIG_COMPAT
>> +	unsafe_copy_siginfo_to_user(&frame->info, &ksig->info, failed);
>> +#endif
>>   
>>   	/* create a stack frame for the caller of the handler */
>>   	unsafe_put_user(regs->gpr[1], newsp, failed);
>>   
>>   	user_access_end();
>>   
>> -	if (copy_siginfo_to_user(&frame->info, &ksig->info))
>> +#ifdef CONFIG_COMPAT
>> +	if (copy_siginfo_to_user32(&frame->info, &ksig->info))
>>   		goto badframe;
>> +#endif
>>   
>>   	regs->link = tramp;
>>   
>> diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
>> index 2cca6c8febe1..82b73fbd937d 100644
>> --- a/arch/powerpc/kernel/signal_64.c
>> +++ b/arch/powerpc/kernel/signal_64.c
>> @@ -901,15 +901,12 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
>>   	}
>>   
>>   	unsafe_copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set), badframe_block);
>> +	unsafe_copy_siginfo_to_user(&frame->info, &ksig->info, badframe_block);
>>   	/* Allocate a dummy caller frame for the signal handler. */
>>   	unsafe_put_user(regs->gpr[1], newsp, badframe_block);
>>   
>>   	user_write_access_end();
>>   
>> -	/* Save the siginfo outside of the unsafe block. */
>> -	if (copy_siginfo_to_user(&frame->info, &ksig->info))
>> -		goto badframe;
>> -
>>   	/* Make sure signal handler doesn't get spurious FP exceptions */
>>   	tsk->thread.fp_state.fpscr = 0;