Re: [PATCH 18/62] x86/boot/compressed/64: Setup GHCB Based VC Exception handler

[Joerg Roedel]

On Tue, Feb 11, 2020 at 02:25:49PM -0800, Andy Lutomirski wrote:
> On Tue, Feb 11, 2020 at 5:53 AM Joerg Roedel <joro@xxxxxxxxxx> wrote:
> >
> > From: Joerg Roedel <jroedel@xxxxxxx>
> >
> > Install an exception handler for #VC exception that uses a GHCB. Also
> > add the infrastructure for handling different exit-codes by decoding
> > the instruction that caused the exception and error handling.
> >
> 
> > diff --git a/arch/x86/boot/compressed/sev-es.c b/arch/x86/boot/compressed/sev-es.c
> > index 8d13121a8cf2..02fb6f57128b 100644
> > --- a/arch/x86/boot/compressed/sev-es.c
> > +++ b/arch/x86/boot/compressed/sev-es.c
> > @@ -8,12 +8,16 @@
> >  #include <linux/kernel.h>
> >
> >  #include <asm/sev-es.h>
> > +#include <asm/trap_defs.h>
> >  #include <asm/msr-index.h>
> >  #include <asm/ptrace.h>
> >  #include <asm/svm.h>
> >
> >  #include "misc.h"
> >
> > +struct ghcb boot_ghcb_page __aligned(PAGE_SIZE);
> > +struct ghcb *boot_ghcb;
> > +
> >  static inline u64 read_ghcb_msr(void)
> >  {
> >         unsigned long low, high;
> > @@ -35,8 +39,95 @@ static inline void write_ghcb_msr(u64 val)
> >                         "a"(low), "d" (high) : "memory");
> >  }
> >
> > +static enum es_result es_fetch_insn_byte(struct es_em_ctxt *ctxt,
> > +                                        unsigned int offset,
> > +                                        char *buffer)
> > +{
> > +       char *rip = (char *)ctxt->regs->ip;
> > +
> > +       buffer[offset] = rip[offset];
> > +
> > +       return ES_OK;
> > +}
> > +
> > +static enum es_result es_write_mem(struct es_em_ctxt *ctxt,
> > +                                  void *dst, char *buf, size_t size)
> > +{
> > +       memcpy(dst, buf, size);
> > +
> > +       return ES_OK;
> > +}
> > +
> > +static enum es_result es_read_mem(struct es_em_ctxt *ctxt,
> > +                                 void *src, char *buf, size_t size)
> > +{
> > +       memcpy(buf, src, size);
> > +
> > +       return ES_OK;
> > +}
> 
> 
> What are all these abstractions for?

They are needed for the code in arch/x86/kernel/sev-es-shared.c. This
file is used in the pre-decompression boot code and in the running
kernels SEV-ES support.

The running kernel needs these abstraction because it will get #VC
exceptions from user-space and MMIO exits touching user-space addresses.
These functions will implement the necessary security checks.

Regards,

	Joerg