[PATCH v4 6/6] x86/sev-es: Propagate #GP if getting linear instruction address failed

From: Joerg Roedel <joro@8bytes.org>
To: x86@kernel.org
Cc: Joerg Roedel <joro@8bytes.org>, Joerg Roedel <jroedel@suse.de>,
	hpa@zytor.com, Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Jiri Slaby <jslaby@suse.cz>,
	Dan Williams <dan.j.williams@intel.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Juergen Gross <jgross@suse.com>,
	Kees Cook <keescook@chromium.org>,
	David Rientjes <rientjes@google.com>,
	Cfir Cohen <cfir@google.com>, Erdem Aktas <erdemaktas@google.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Mike Stunes <mstunes@vmware.com>,
	Sean Christopherson <seanjc@google.com>,
	Martin Radev <martin.b.radev@gmail.com>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, virtualization@lists.linux-foundation.org
Subject: [PATCH v4 6/6] x86/sev-es: Propagate #GP if getting linear instruction address failed
Date: Thu, 10 Jun 2021 11:11:41 +0200	[thread overview]
Message-ID: <20210610091141.30322-7-joro@8bytes.org> (raw)
In-Reply-To: <20210610091141.30322-1-joro@8bytes.org>

From: Joerg Roedel <jroedel@suse.de>

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 an 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>
---
 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 a7045a5a94ca..80c0d8385def 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -270,11 +270,18 @@ 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))
-- 
2.31.1

