diff mbox series

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

Message ID 20210512075445.18935-5-joro@8bytes.org
State New
Headers show
Series [1/6] x86/sev-es: Don't return NULL from sev_es_get_ghcb() | expand

Commit Message

Joerg Roedel May 12, 2021, 7:54 a.m. UTC 
From: Joerg Roedel <jroedel@suse.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@vger.kernel.org # v5.11
Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
 arch/x86/kernel/sev.c | 12 ------------
 1 file changed, 12 deletions(-)

Comments

Joerg Roedel May 19, 2021, 12:22 p.m. UTC | #1 
On Wed, May 12, 2021 at 05:38:29PM +0000, Sean Christopherson wrote:
> Alternatively, and probably even better, fold this revert into the switch to

> the unchecked version (sounds like those will use kernel-specific flavors?).


I folded this revert into the previous commit. But I kept the
__get_user()/__put_user() calls and just added a comment explaining why
they are used and why it is safe to use them.

After all, even the get_kernel*() functions call __get_user_size() under
the hood.

Regards,

	Joerg
diff mbox series

Patch

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))