Re: [PATCH] i386 uaccess to fixmap pages

[Andrew Morton]

Roland McGrath <[e-mail]> wrote:
>
> This patch against 2.5.69 makes uaccess (i.e., access_ok and get/put_user)
> to user-accessible fixmap addresses on x86 work.

This doesn't apply against Linus's current tree.

> -#define access_ok(type,addr,size) (__range_ok(addr,size) == 0)
> +#define access_ok(type,addr,size) (__range_ok(addr,size) == 0 || \
> +				   __fixmap_access_ok((unsigned long)(addr), \
> +						      (size), (type)))

Your patch increases the kernel text by nearly 1%.  That's rather a lot for
what is a fairly esoteric feature.

   text    data     bss     dec     hex filename
2805911  592912  732516 4131339  3f0a0b /tmp/vmlinux
2825167  592982  732516 4150665  3f5589 vmlinux

Would it be possible to avoid this by just taking the fault and fixing
things up in the exception handler?

>  #else
>  
> -#define access_ok(type,addr,size) ( (__range_ok(addr,size) == 0) && \
> +#define access_ok(type,addr,size) ((__range_ok(addr,size) == 0) ? \
>  			 ((type) == VERIFY_READ || boot_cpu_data.wp_works_ok || \
> -			  __verify_write((void *)(addr),(size))))
> +			  __verify_write((void *)(addr),(size))) : \
> +			  __fixmap_access_ok((unsigned long)(addr),size,type))

You'll be wanting to parenthesise `size' and `type' here.

For some reason the patch causes gcc-2.95.3 to choke over the

	__put_user(d_off, &lastdirent->d_off);

statement in sys_getdents64().

fs/readdir.c: In function `sys_getdents64':
fs/readdir.c:285: internal error--unrecognizable insn:
(insn 138 212 147 (set (reg:SI 3 %ebx)
        (asm_operands/v ("1:	movl %%eax,0(%2)
2:	movl %%edx,4(%2)
3:
.section .fixup,"ax"
4:	movl %3,%0
	jmp 3b
.previous
.section __ex_table,"a"
	.align 4
	.long 1b,4b
	.long 2b,4b
.previous") ("=r") 0[ 
                (reg:DI 1 %edx)
                (reg:SI 0 %eax)
                (const_int -14 [0xfffffff2])
                (reg:SI 3 %ebx)
            ] 
            [ 
                (asm_input:DI ("A"))
                (asm_input:SI ("r"))
                (asm_input:SI ("i"))
                (asm_input:SI ("0"))
            ]  ("fs/readdir.c") 277)) -1 (insn_list 112 (insn_list 119 (insn_list 137 (nil))))
    (nil))
make[1]: *** [fs/readdir.o] Error 1
make[1]: *** Waiting for unfinished jobs....
make: *** [fs] Error 2