On 11/09/15 18:00, Russell King - ARM Linux wrote:
> On Fri, Sep 11, 2015 at 05:25:59PM +0100, Julien Grall wrote:
>> + /*
>> + * Privcmd calls are issued by the userspace. We need to allow the
>> + * kernel to access the userspace memory before issuing the hypercall.
>> + */
>> + uaccess_enable r4
>> +
>> + /* r4 is loaded now as we use it as scratch register before */
>> ldr r4, [sp, #4]
>
> As I mentioned in one of my previous mails, "ip" should be safe to use
> here - it's a caller-corrupted register, just like r0-r3 and lr. So,
> you could do:
>
> ldr r4, [sp, #4]
> + uaccess_enable ip
The register ip (aka r12) is used to store the hypercall number. So we
can't reuse it as scratch register.
The easiest one is r4.
>
> which fractionally tightens the window.
>
> However, there's nothing actually wrong with your version - there's no
> way we could've got this far with sp pointing at userspace.
>
> I'm happy with either version, so:
>
> Acked-by: Russell King <rmk+ker...@arm.linux.org.uk>
>
> How do you want to handle the patch? I already have some other uaccess
> fixes queued up to send to Linus before the merge window closes.
>
>> __HVC(XEN_IMM)
>> +
>> + /*
>> + * Disable userspace access from kernel. This is fine to do it
>> + * unconditionally as no set_fs(KERNEL_DS)/set_fs(get_ds()) is
>> + * called before.
>> + */
>> + uaccess_disable r4
>> +
>> ldm sp!, {r4}
>> ret lr
>> ENDPROC(privcmd_call);
>> --
>> 2.1.4
>>
>
--
Julien Grall
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