Re: [Xen-devel] [PATCH] arm/xen: Enable user access to the kernel before issuing a privcmd call

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2015-09-11 at 15:45 +0100, Julien Grall wrote:
> On 11/09/15 15:29, Ian Campbell wrote:
> > On Fri, 2015-09-11 at 15:16 +0100, Julien Grall wrote:
> > > When Xen is copyin data to/from the guest it will check if the kernel
> > 
> > "copying"
> > 
> > > has the right to do the access. If not, the hypercall will return an
> > > error.
> > > 
> > > After the commit a5e090acbf545c0a3b04080f8a488b17ec41fe02 "ARM:
> > > software-based priviledged-no-access support", the kernel can't
> > > access
> > 
> > "privileged"
> > 
> > > anymore the user space by default. This will result to fail on every
> > 
> > "any more" (or "any longer")
> > 
> > > hypercall made by the userspace (i.e via privcmd).
> > > 
> > > We have to enable the userspace access and then restore the correct
> > > permission everytime the privmcd is used to made an hypercall.
> > 
> > "every time" and "privcmd"
> > 
> > >  HYPERCALL1(tmem_op);
> > >  HYPERCALL2(multicall);
> > >  
> > > -ENTRY(privcmd_call)
> > > +ENTRY(__privcmd_call)
> > 
> > arch/arm/include/asm/assembler.h seems to contain uaccess_* macros
> > which
> > could be used right here directly I think? That would be preferable to
> > wrapping I think.
> 
> Looking to the uaccess_save macro:

I was thinking more about uaccess_enable/disable.

Ian.

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