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Subject[tip: x86/urgent] x86/sev-es: Handle string port IO to kernel memory properly
The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: 7024f60d655272bd2ca1d3a4c9e0a63319b1eea1
Gitweb: https://git.kernel.org/tip/7024f60d655272bd2ca1d3a4c9e0a63319b1eea1
Author: Hyunwook (Wooky) Baek <baekhw@google.com>
AuthorDate: Sat, 09 Jan 2021 23:11:02 -08:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Mon, 11 Jan 2021 20:01:52 +01:00

x86/sev-es: Handle string port IO to kernel memory properly

Don't assume dest/source buffers are userspace addresses when manually
copying data for string I/O or MOVS MMIO, as {get,put}_user() will fail
if handed a kernel address and ultimately lead to a kernel panic.

When invoking INSB/OUTSB instructions in kernel space in a
SEV-ES-enabled VM, the kernel crashes with the following message:

"SEV-ES: Unsupported exception in #VC instruction emulation - can't continue"

Handle that case properly.

[ bp: Massage commit message. ]

Fixes: f980f9c31a92 ("x86/sev-es: Compile early handler code into kernel image")
Signed-off-by: Hyunwook (Wooky) Baek <baekhw@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: David Rientjes <rientjes@google.com>
Link: https://lkml.kernel.org/r/20210110071102.2576186-1-baekhw@google.com
---
arch/x86/kernel/sev-es.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 0bd1a0f..ab31c34 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -286,6 +286,12 @@ 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);
@@ -335,6 +341,12 @@ 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))
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