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[xen stable-4.13] x86/EPT: ept_set_middle_entry() related adjustments
commit 56e117f504f83d1576bf62b53bf70e4a82e2a877
Author: Jan Beulich <jbeulich@suse.com>
AuthorDate: Tue Jul 7 15:01:08 2020 +0200
Commit: Jan Beulich <jbeulich@suse.com>
CommitDate: Tue Jul 7 15:01:08 2020 +0200

x86/EPT: ept_set_middle_entry() related adjustments

ept_split_super_page() wants to further modify the newly allocated
table, so have ept_set_middle_entry() return the mapped pointer rather
than tearing it down and then getting re-established right again.

Similarly ept_next_level() wants to hand back a mapped pointer of
the next level page, so re-use the one established by
ept_set_middle_entry() in case that path was taken.

Pull the setting of suppress_ve ahead of insertion into the higher level
table, and don't have ept_split_super_page() set the field a 2nd time.

This is part of XSA-328.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
master commit: 1104288186ee73a7f9bfa41cbaa5bb7611521028
master date: 2020-07-07 14:36:52 +0200
---
xen/arch/x86/mm/p2m-ept.c | 41 ++++++++++++++++++-----------------------
1 file changed, 18 insertions(+), 23 deletions(-)

diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
index b5517769c9..9abbd9e680 100644
--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -187,8 +187,9 @@ static void ept_p2m_type_to_flags(struct p2m_domain *p2m, ept_entry_t *entry,
#define GUEST_TABLE_SUPER_PAGE 2
#define GUEST_TABLE_POD_PAGE 3

-/* Fill in middle levels of ept table */
-static int ept_set_middle_entry(struct p2m_domain *p2m, ept_entry_t *ept_entry)
+/* Fill in middle level of ept table; return pointer to mapped new table. */
+static ept_entry_t *ept_set_middle_entry(struct p2m_domain *p2m,
+ ept_entry_t *ept_entry)
{
mfn_t mfn;
ept_entry_t *table;
@@ -196,7 +197,12 @@ static int ept_set_middle_entry(struct p2m_domain *p2m, ept_entry_t *ept_entry)

mfn = p2m_alloc_ptp(p2m, 0);
if ( mfn_eq(mfn, INVALID_MFN) )
- return 0;
+ return NULL;
+
+ table = map_domain_page(mfn);
+
+ for ( i = 0; i < EPT_PAGETABLE_ENTRIES; i++ )
+ table[i].suppress_ve = 1;

ept_entry->epte = 0;
ept_entry->mfn = mfn_x(mfn);
@@ -208,14 +214,7 @@ static int ept_set_middle_entry(struct p2m_domain *p2m, ept_entry_t *ept_entry)

ept_entry->suppress_ve = 1;

- table = map_domain_page(mfn);
-
- for ( i = 0; i < EPT_PAGETABLE_ENTRIES; i++ )
- table[i].suppress_ve = 1;
-
- unmap_domain_page(table);
-
- return 1;
+ return table;
}

/* free ept sub tree behind an entry */
@@ -253,10 +252,10 @@ static bool_t ept_split_super_page(struct p2m_domain *p2m,

ASSERT(is_epte_superpage(ept_entry));

- if ( !ept_set_middle_entry(p2m, &new_ept) )
+ table = ept_set_middle_entry(p2m, &new_ept);
+ if ( !table )
return 0;

- table = map_domain_page(_mfn(new_ept.mfn));
trunk = 1UL << ((level - 1) * EPT_TABLE_ORDER);

for ( i = 0; i < EPT_PAGETABLE_ENTRIES; i++ )
@@ -267,7 +266,6 @@ static bool_t ept_split_super_page(struct p2m_domain *p2m,
epte->sp = (level > 1);
epte->mfn += i * trunk;
epte->snp = is_iommu_enabled(p2m->domain) && iommu_snoop;
- epte->suppress_ve = 1;

ept_p2m_type_to_flags(p2m, epte, epte->sa_p2mt, epte->access);

@@ -306,8 +304,7 @@ static int ept_next_level(struct p2m_domain *p2m, bool_t read_only,
ept_entry_t **table, unsigned long *gfn_remainder,
int next_level)
{
- unsigned long mfn;
- ept_entry_t *ept_entry, e;
+ ept_entry_t *ept_entry, *next = NULL, e;
u32 shift, index;

shift = next_level * EPT_TABLE_ORDER;
@@ -332,19 +329,17 @@ static int ept_next_level(struct p2m_domain *p2m, bool_t read_only,
if ( read_only )
return GUEST_TABLE_MAP_FAILED;

- if ( !ept_set_middle_entry(p2m, ept_entry) )
+ next = ept_set_middle_entry(p2m, ept_entry);
+ if ( !next )
return GUEST_TABLE_MAP_FAILED;
- else
- e = atomic_read_ept_entry(ept_entry); /* Refresh */
+ /* e is now stale and hence may not be used anymore below. */
}
-
/* The only time sp would be set here is if we had hit a superpage */
- if ( is_epte_superpage(&e) )
+ else if ( is_epte_superpage(&e) )
return GUEST_TABLE_SUPER_PAGE;

- mfn = e.mfn;
unmap_domain_page(*table);
- *table = map_domain_page(_mfn(mfn));
+ *table = next ?: map_domain_page(_mfn(e.mfn));
*gfn_remainder &= (1UL << shift) - 1;
return GUEST_TABLE_NORMAL_PAGE;
}
--
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