linux-kernel - Re: [PATCH 3/3] riscv: fix __user annotation for __copy

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Message-ID: <20180607165131.5qx43o6f2siwyivj@ltop.local>
Date:   Thu, 7 Jun 2018 18:51:33 +0200
From:   Luc Van Oostenryck <luc.vanoostenryck@...il.com>
To:     Palmer Dabbelt <palmer@...ive.com>
Cc:     atish.patra@....com, linux-riscv@...ts.infradead.org,
        albert@...ive.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] riscv: fix __user annotation for __copy_user()

On Thu, Jun 07, 2018 at 09:30:19AM -0700, Palmer Dabbelt wrote:
> 
> I haven't compiled this, but I think it should work.  It's on the
> fix-sparse branch of kernel.org/palmer/linux.git .

It's essentially what I was thinking but I have some small remarks.
 
> diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
> index 14b0b22fb578..0dbbbab05dac 100644
> --- a/arch/riscv/include/asm/uaccess.h
> +++ b/arch/riscv/include/asm/uaccess.h
> @@ -392,19 +392,21 @@ do {								\
> })
> 
> 
> -extern unsigned long __must_check __copy_user(void __user *to,
> +extern unsigned long __must_check __asm_copy_from_user_user(void *to,
> 	const void __user *from, unsigned long n);
> +extern unsigned long __must_check __asm_copy_to_user_user(void __user *to,
> +	const void *from, unsigned long n);
> 
> static inline unsigned long
> raw_copy_from_user(void *to, const void __user *from, unsigned long n)
> {
> -	return __copy_user(to, from, n);
> +	return __asm_copy_from_user(to, from, n);
> }
> 
> static inline unsigned long
> raw_copy_to_user(void __user *to, const void *from, unsigned long n)
> {
> -	return __copy_user(to, from, n);
> +	return __asm_copy_to_user(to, from, n);
> }

The asm function could have directly be named raw_copy_{to,from}_user()
because the inline functions are just no-ops but it's very clear like so.

> extern long strncpy_from_user(char *dest, const char __user *src, long count);
> diff --git a/arch/riscv/lib/uaccess.S b/arch/riscv/lib/uaccess.S
> index 58fb2877c865..bd51e47ebd44 100644
> --- a/arch/riscv/lib/uaccess.S
> +++ b/arch/riscv/lib/uaccess.S
> @@ -13,7 +13,15 @@ _epc:
> 	.previous
> 	.endm
> 
> -ENTRY(__copy_user)
> +/* __asm_copy_to_user and __asm_copy_from_user are actually the same function,
> + * they're just provided as two different symbols to C code so sparse doesn't
> + * yell about casting between two different address spaces. */
> +.global __asm_copy_to_user
> +.set __asm_copy_to_user,__asm_copy_tofrom_user
> +.global __asm_copy_from_user
> +.set __asm_copy_from_user,__asm_copy_tofrom_user
> +
> +ENTRY(__asm_copy_tofrom_user)

I don't think that the size (as reported by objdump, for example) will
be correct or even present for __asm_copy_to_user & __asm_copy_to_user.

What can be done is:
	ENTRY(__asm_copy_to_user)
	ENTRY(__asm_copy_from_user)

	<function definition>

	ENDPROC(__asm_copy_to_user)
	ENDPROC(__asm_copy_from_user)


Finally, the symbol table need also something like:
diff --git a/arch/riscv/kernel/riscv_ksyms.c b/arch/riscv/kernel/riscv_ksyms.c
index 551734248..1e8f8fa54 100644
--- a/arch/riscv/kernel/riscv_ksyms.c
+++ b/arch/riscv/kernel/riscv_ksyms.c
@@ -13,6 +13,7 @@
  * Assembly functions that may be used (directly or indirectly) by modules
  */
 EXPORT_SYMBOL(__clear_user);
-EXPORT_SYMBOL(__copy_user);
+EXPORT_SYMBOL(__asm_copy_to_user);
+EXPORT_SYMBOL(__asm_copy_from_user);
 EXPORT_SYMBOL(memset);
 EXPORT_SYMBOL(memcpy);


Best regards,
-- Luc