Re: [PATCH v3 52/75] x86/sev-es: Handle MMIO String Instructions
From: Borislav Petkov <bp@alien8.de>
Date: 2020-05-25 09:48:04
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On Tue, Apr 28, 2020 at 05:17:02PM +0200, Joerg Roedel wrote:
quoted hunk ↗ jump to hunk
From: Joerg Roedel <redacted> Add handling for emulation the MOVS instruction on MMIO regions, as done by the memcpy_toio() and memcpy_fromio() functions. Signed-off-by: Joerg Roedel <redacted> --- arch/x86/kernel/sev-es.c | 78 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 78 insertions(+)diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c index e3662723ed76..84958a82f8e0 100644 --- a/arch/x86/kernel/sev-es.c +++ b/arch/x86/kernel/sev-es.c@@ -552,6 +552,74 @@ 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, this code splits
s/this code splits/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);
+^ Superfluous newline.
quoted hunk ↗ jump to hunk
+ 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) {@@ -606,6 +674,16 @@ 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 */
WARNING: Prefer 'fallthrough;' over fallthrough comment
#120: FILE: arch/x86/kernel/sev-es.c:680:
+ /* Fallthrough */
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette