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

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index a170810..f724b75 100644 (file)
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -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);