Re: [PATCH] x86/uaccess: Implement get_kernel()

Ingo Molnar
2015-04-10T18:04:59Z

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Fri, Apr 10, 2015 at 01:14:27PM +0200, Ingo Molnar wrote:
> > +/*
> > + * Simple copy-from-possibly-faulting-kernel-addresses method that
> > + * avoids the STAC/CLAC SMAP overhead.
> > + *
> > + * NOTE: this does not propagate the error code of faulting kernel
> > + * addresses properly. You can recover it via uaccess_catch()
> > + * if you really need to.
> > + */
> > +#define get_kernel(dst, src) \
> > +do { \
> > + typeof(*(src)) __val; \
>
> Should we make that:
>
> typeof(*(src)) __val = (dst);
>
> > + \
> > + switch (sizeof(__val)) { \
> > + case 1: __get_kernel_asm_ex(__val, src, "b", "b", "=q"); break; \
> > + case 2: __get_kernel_asm_ex(__val, src, "w", "w", "=r"); break; \
> > + case 4: __get_kernel_asm_ex(__val, src, "l", "k", "=r"); break; \
> > + case 8: __get_kernel_asm_ex(__val, src, "q", " ", "=r"); break; \
> > + default: __get_kernel_BUILD_ERROR(); \
> > + } \
> > + (dst) = __val; \
> > +} while (0)
>
> Such that when we fault, the value is unmodified? The way it is we'll
> assign whatever was on stack for __val, which seems undesirable, no?

Yes, indeed.

Thanks,

Ingo