File xsa299-2.patch of Package xen.21123

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File xsa299-2.patch of Package xen.21123

From fcfb3fc77052d328273a98e4f360354af660affe Mon Sep 17 00:00:00 2001
From: George Dunlap <george.dunlap@citrix.com>
Date: Thu, 10 Oct 2019 17:57:49 +0100
Subject: [PATCH 02/12] x86/mm: L1TF checks don't leave a partial entry

On detection of a potential L1TF issue, most validation code returns
-ERESTART to allow the switch to shadow mode to happen and cause the
original operation to be restarted.

However, in the validation code, the return value -ERESTART has been
repurposed to indicate 1) the function has partially completed
something which needs to be undone, and 2) calling put_page_type()
should cleanly undo it.  This causes problems in several places.

For L1 tables, on receiving an -ERESTART return from alloc_l1_table(),
alloc_page_type() will set PGT_partial on the page.  If for some
reason the original operation never restarts, then on domain
destruction, relinquish_memory() will call free_page_type() on the
page.

Unfortunately, alloc_ and free_l1_table() aren't set up to deal with
PGT_partial.  When returning a failure, alloc_l1_table() always
de-validates whatever it's validated so far, and free_l1_table()
always devalidates the whole page.  This means that if
relinquish_memory() calls free_page_type() on an L1 that didn't
complete due to an L1TF, it will call put_page_from_l1e() on "page
entries" that have never been validated.

For L2+ tables, setting rc to ERESTART causes the rest of the
alloc_lN_table() function to *think* that the entry in question will
have PGT_partial set.  This will cause it to set partial_pte = 1.  If
relinqush_memory() then calls free_page_type() on one of those pages,
then free_lN_table() will call put_page_from_lNe() on the entry when
it shouldn't.

Rather than indicating -ERESTART, indicate -EINTR.  This is the code
to indicate that nothing has changed from when you started the call
(which is effectively how alloc_l1_table() handles errors).

mod_lN_entry() shouldn't have any of these types of problems, so leave
potential changes there for a clean-up patch later.

This is part of XSA-299.

Reported-by: George Dunlap <george.dunlap@citrix.com>
Signed-off-by: George Dunlap <george.dunlap@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
 xen/arch/x86/mm.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -1235,7 +1235,7 @@ get_page_from_l2e(
     int rc;
 
     if ( !(l2e_get_flags(l2e) & _PAGE_PRESENT) )
-        return pv_l1tf_check_l2e(d, l2e) ? -ERESTART : 1;
+        return pv_l1tf_check_l2e(d, l2e) ? -EINTR : 1;
 
     if ( unlikely((l2e_get_flags(l2e) & L2_DISALLOW_MASK)) )
     {
@@ -1277,7 +1277,7 @@ get_page_from_l3e(
     int rc;
 
     if ( !(l3e_get_flags(l3e) & _PAGE_PRESENT) )
-        return pv_l1tf_check_l3e(d, l3e) ? -ERESTART : 1;
+        return pv_l1tf_check_l3e(d, l3e) ? -EINTR : 1;
 
     if ( unlikely((l3e_get_flags(l3e) & l3_disallow_mask(d))) )
     {
@@ -1303,7 +1303,7 @@ get_page_from_l4e(
     int rc;
 
     if ( !(l4e_get_flags(l4e) & _PAGE_PRESENT) )
-        return pv_l1tf_check_l4e(d, l4e) ? -ERESTART : 1;
+        return pv_l1tf_check_l4e(d, l4e) ? -EINTR : 1;
 
     if ( unlikely((l4e_get_flags(l4e) & L4_DISALLOW_MASK)) )
     {
@@ -1568,7 +1568,7 @@ static int alloc_l1_table(struct page_in
         {
             if ( !(l1e_get_flags(pl1e[i]) & _PAGE_PRESENT) )
             {
-                ret = pv_l1tf_check_l1e(d, pl1e[i]) ? -ERESTART : 0;
+                ret = pv_l1tf_check_l1e(d, pl1e[i]) ? -EINTR : 0;
                 if ( ret )
                     goto out;
             }

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File xsa299-2.patch of Package xen.21123

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