Re: [Xen-devel] Weird overflowing user_desc assignment

[Chris Wright <chrisw@xxxxxxxxxxxx>]

* Stephen C. Tweedie (sct@xxxxxxxxxx) wrote:
> static inline void set_32bit_tls(struct task_struct *t, int tls, u32
> addr)
> {
>       struct user_desc ud = { 
>               .base_addr = addr,
>               .limit = 0xfffff,
>               .contents = (3 << 3), /* user */
>               .seg_32bit = 1,
>               .limit_in_pages = 1,
>               .useable = 1,
>       };
>       struct n_desc_struct *desc = (void *)t->thread.tls_array;
>       desc += tls;
>       desc->a = LDT_entry_a(&ud); 
>       desc->b = LDT_entry_b(&ud); 
> }
> 
> where we get an overflow assigning "3 << 3" to ud.contents, which is a
> 2-bit bitfield defined in include/asm-x86_64/ldt.h:
> 
> struct user_desc {
> ...
>       unsigned int  contents:2;
> ...
> };
> 
> Any idea what the intention was here?

And why this was never picked up?

http://lists.xensource.com/archives/html/xen-devel/2006-02/msg00640.html

thanks,
-chris

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