linux-kernel - [PATCH 4/6] Revert "x86/sev-es: Handle string port IO to kernel memory properly"

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Date:   Wed, 12 May 2021 09:54:43 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     x86@...nel.org, Hyunwook Baek <baekhw@...gle.com>
Cc:     Joerg Roedel <joro@...tes.org>, Joerg Roedel <jroedel@...e.de>,
        stable@...r.kernel.org, hpa@...or.com,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Martin Radev <martin.b.radev@...il.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: [PATCH 4/6] Revert "x86/sev-es: Handle string port IO to kernel memory properly"

From: Joerg Roedel <jroedel@...e.de>

This reverts commit 7024f60d655272bd2ca1d3a4c9e0a63319b1eea1.

The commit reverted here introduces a short-cut into the #VC handlers
memory access code which only works reliably in task context. But the
kernels #VC handler can be invoked from any context, making the
access_ok() call trigger a warning with CONFIG_DEBUG_ATOMIC_SLEEP
enabled.

Also the memcpy() used in the reverted patch is wrong, as it has no
page-fault handling. Access to kernel memory can also fault due to
kernel bugs, and those should not be reported as faults from the #VC
handler but as bugs of their real call-site, which is correctly later
done from vc_forward_exception().

Fixes: 7024f60d6552 ("x86/sev-es: Handle string port IO to kernel memory properly")
Cc: stable@...r.kernel.org # v5.11
Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/kernel/sev.c | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 110b39345b40..f4f319004713 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -333,12 +333,6 @@ static enum es_result vc_write_mem(struct es_em_ctxt *ctxt,
 	u16 d2;
 	u8  d1;
 
-	/* If instruction ran in kernel mode and the I/O buffer is in kernel space */
-	if (!user_mode(ctxt->regs) && !access_ok(target, size)) {
-		memcpy(dst, buf, size);
-		return ES_OK;
-	}
-
 	switch (size) {
 	case 1:
 		memcpy(&d1, buf, 1);
@@ -388,12 +382,6 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt,
 	u16 d2;
 	u8  d1;
 
-	/* If instruction ran in kernel mode and the I/O buffer is in kernel space */
-	if (!user_mode(ctxt->regs) && !access_ok(s, size)) {
-		memcpy(buf, src, size);
-		return ES_OK;
-	}
-
 	switch (size) {
 	case 1:
 		if (__get_user(d1, s))
-- 
2.31.1