x86/sev: Propagate #GP if getting linear instruction address failed

When an instruction is fetched from user-space, segmentation needs to
be taken into account. This means that getting the linear address of an
instruction can fail. Hardware would raise a #GP exception in that case,
but the #VC exception handler would emulate it as a page-fault.

The insn_fetch_from_user*() functions now provide the relevant
information in case of a failure. Use that and propagate a #GP when the
linear address of an instruction to fetch could not be calculated.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210614135327.9921-7-joro@8bytes.org

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index a1eeaa79bf2bfb5c4a770d0d6118eb985b40799f..8178db07a06a656f48a82a567d0d81d8e9a49cc8 100644 (file)
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -261,11 +261,18 @@ static enum es_result __vc_decode_user_insn(struct es_em_ctxt *ctxt)
        int insn_bytes;
 
        insn_bytes = insn_fetch_from_user_inatomic(ctxt->regs, buffer);
-       if (insn_bytes <= 0) {
+       if (insn_bytes == 0) {
+               /* Nothing could be copied */
                ctxt->fi.vector     = X86_TRAP_PF;
                ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER;
                ctxt->fi.cr2        = ctxt->regs->ip;
                return ES_EXCEPTION;
+       } else if (insn_bytes == -EINVAL) {
+               /* Effective RIP could not be calculated */
+               ctxt->fi.vector     = X86_TRAP_GP;
+               ctxt->fi.error_code = 0;
+               ctxt->fi.cr2        = 0;
+               return ES_EXCEPTION;
        }
 
        if (!insn_decode_from_regs(&ctxt->insn, ctxt->regs, buffer, insn_bytes))