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x86/sev-es: Handle MMIO String Instructions 

Add handling for emulation of the MOVS instruction on MMIO regions, as
done by the memcpy_toio() and memcpy_fromio() functions.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-51-joro@8bytes.org
This commit is contained in:
Joerg Roedel 2020-09-07 15:15:51 +02:00 committed by Borislav Petkov
parent 51ee7d6e3d
commit 0118b604c2
1 changed files with 77 additions and 0 deletions
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77
arch/x86/kernel/sev-es.c
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@ -594,6 +594,73 @@ static enum es_result vc_handle_mmio_twobyte_ops(struct ghcb *ghcb,
return ret;
}
/*
* The MOVS instruction has two memory operands, which raises the
* problem that it is not known whether the access to the source or the
* destination caused the #VC exception (and hence whether an MMIO read
* or write operation needs to be emulated).
*
* Instead of playing games with walking page-tables and trying to guess
* whether the source or destination is an MMIO range, split the move
* into two operations, a read and a write with only one memory operand.
* This will cause a nested #VC exception on the MMIO address which can
* then be handled.
*
* This implementation has the benefit that it also supports MOVS where
* source _and_ destination are MMIO regions.
*
* It will slow MOVS on MMIO down a lot, but in SEV-ES guests it is a
* rare operation. If it turns out to be a performance problem the split
* operations can be moved to memcpy_fromio() and memcpy_toio().
*/
static enum es_result vc_handle_mmio_movs(struct es_em_ctxt *ctxt,
unsigned int bytes)
{
unsigned long ds_base, es_base;
unsigned char *src, *dst;
unsigned char buffer[8];
enum es_result ret;
bool rep;
int off;
ds_base = insn_get_seg_base(ctxt->regs, INAT_SEG_REG_DS);
es_base = insn_get_seg_base(ctxt->regs, INAT_SEG_REG_ES);
if (ds_base == -1L || es_base == -1L) {
ctxt->fi.vector = X86_TRAP_GP;
ctxt->fi.error_code = 0;
return ES_EXCEPTION;
}
src = ds_base + (unsigned char *)ctxt->regs->si;
dst = es_base + (unsigned char *)ctxt->regs->di;
ret = vc_read_mem(ctxt, src, buffer, bytes);
if (ret != ES_OK)
return ret;
ret = vc_write_mem(ctxt, dst, buffer, bytes);
if (ret != ES_OK)
return ret;
if (ctxt->regs->flags & X86_EFLAGS_DF)
off = -bytes;
else
off = bytes;
ctxt->regs->si += off;
ctxt->regs->di += off;
rep = insn_has_rep_prefix(&ctxt->insn);
if (rep)
ctxt->regs->cx -= 1;
if (!rep || ctxt->regs->cx == 0)
return ES_OK;
else
return ES_RETRY;
}
static enum es_result vc_handle_mmio(struct ghcb *ghcb,
struct es_em_ctxt *ctxt)
{
@ -655,6 +722,16 @@ static enum es_result vc_handle_mmio(struct ghcb *ghcb,
memcpy(reg_data, ghcb->shared_buffer, bytes);
break;
/* MOVS instruction */
case 0xa4:
bytes = 1;
fallthrough;
case 0xa5:
if (!bytes)
bytes = insn->opnd_bytes;
ret = vc_handle_mmio_movs(ctxt, bytes);
break;
/* Two-Byte Opcodes */
case 0x0f:
ret = vc_handle_mmio_twobyte_ops(ghcb, ctxt);