Re: [PATCH 3/3] riscv: fix __user annotation for __copy_user()

[Palmer Dabbelt]

On Thu, 07 Jun 2018 09:51:33 PDT (-0700), luc.vanoostenr...@gmail.com wrote:

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);

Thanks.  Do you mind checking to make sure this works and submitting a patch?