linux-kernel - Re: [PATCH] riscv: fix __user annotation in traps_misaligned.c

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Message-ID: <7232f08e-dfe3-43d6-a4f7-abf8360bbfc1@rivosinc.com>
Date:   Fri, 24 Nov 2023 11:28:08 +0100
From:   Clément Léger <cleger@...osinc.com>
To:     Christoph Hellwig <hch@...radead.org>,
        Ben Dooks <ben.dooks@...ethink.co.uk>
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu
Subject: Re: [PATCH] riscv: fix __user annotation in traps_misaligned.c

On 24/11/2023 07:05, Christoph Hellwig wrote:
> On Thu, Nov 23, 2023 at 02:16:17PM +0000, Ben Dooks wrote:
>> @@ -319,7 +319,7 @@ static inline int get_insn(struct pt_regs *regs, ulong mepc, ulong *r_insn)
>>  static inline int load_u8(struct pt_regs *regs, const u8 *addr, u8 *r_val)
>>  {
>>  	if (user_mode(regs)) {
>> -		return __get_user(*r_val, addr);
>> +		return __get_user(*r_val, (u8 __user *)addr);
>>  	} else {
>>  		*r_val = *addr;
>>  		return 0;
> 
> This is the wrong way to approach it.  Pass the untype unsigned long
> from the caller instead and do a single round of casts from that
> depending on the address_space.

I sent a similar patch two days ago with the same modification. I'm not
sure to get it. Why is it better to pass the "unsigned long" type from
the caller ? I mean, the resulting code would look like this right ?

static inline int store_u8(struct pt_regs *regs, unsigned long addr, u8 val)
{
	if (user_mode(regs)) {
		return __put_user(val, (u8 __user *)addr);
	} else {
		*addr = (u8 *)val;
		return 0;
	}
}

Is this better from a "semantic" point of view and be sure the casts are
done in a single place ?

> 
> And please also remove this horrible else after return entipattern
> while you're at it.

Acked,

Thanks,

> 
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

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