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

[tip-bot2 for Joerg Roedel]

The following commit has been merged into the x86/sev branch of tip:

Commit-ID:     07570cef5e5c3fcec40f82a9075abb4c1da63319
Gitweb:        https://git.kernel.org/tip/07570cef5e5c3fcec40f82a9075abb4c1da63319
Author:        Joerg Roedel <jroedel@xxxxxxx>
AuthorDate:    Mon, 14 Jun 2021 15:53:27 +02:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Tue, 15 Jun 2021 11:55:26 +02:00

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@xxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lkml.kernel.org/r/20210614135327.9921-7-joro@xxxxxxxxxx
---
 arch/x86/kernel/sev.c |  9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index a1eeaa7..8178db0 100644
--- 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))