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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen staging] x86: protect conditional lock taking from speculative execution
commit 03cf7ca23e0e876075954c558485b267b7d02406
Author: Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Mon Mar 4 16:24:21 2024 +0100
Commit: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Mar 12 15:50:04 2024 +0000
x86: protect conditional lock taking from speculative execution
Conditionally taken locks that use the pattern:
if ( lock )
spin_lock(...);
Need an else branch in order to issue an speculation barrier in the else
case,
just like it's done in case the lock needs to be acquired.
eval_nospec() could be used on the condition itself, but that would result
in a
double barrier on the branch where the lock is taken.
Introduce a new pair of helpers, {gfn,spin}_lock_if() that can be used to
conditionally take a lock in a speculation safe way.
This is part of XSA-453 / CVE-2024-2193
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
xen/arch/x86/mm.c | 35 +++++++++++++----------------------
xen/arch/x86/mm/mm-locks.h | 9 +++++++++
xen/arch/x86/mm/p2m.c | 5 ++---
xen/include/xen/spinlock.h | 8 ++++++++
4 files changed, 32 insertions(+), 25 deletions(-)
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 2ba4c26401..62f5b811bb 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -5018,8 +5018,7 @@ static l3_pgentry_t *virt_to_xen_l3e(unsigned long v)
if ( !l3t )
return NULL;
UNMAP_DOMAIN_PAGE(l3t);
- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);
if ( !(l4e_get_flags(*pl4e) & _PAGE_PRESENT) )
{
l4_pgentry_t l4e = l4e_from_mfn(l3mfn, __PAGE_HYPERVISOR);
@@ -5056,8 +5055,7 @@ static l2_pgentry_t *virt_to_xen_l2e(unsigned long v)
return NULL;
}
UNMAP_DOMAIN_PAGE(l2t);
- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);
if ( !(l3e_get_flags(*pl3e) & _PAGE_PRESENT) )
{
l3e_write(pl3e, l3e_from_mfn(l2mfn, __PAGE_HYPERVISOR));
@@ -5095,8 +5093,7 @@ l1_pgentry_t *virt_to_xen_l1e(unsigned long v)
return NULL;
}
UNMAP_DOMAIN_PAGE(l1t);
- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);
if ( !(l2e_get_flags(*pl2e) & _PAGE_PRESENT) )
{
l2e_write(pl2e, l2e_from_mfn(l1mfn, __PAGE_HYPERVISOR));
@@ -5127,6 +5124,8 @@ l1_pgentry_t *virt_to_xen_l1e(unsigned long v)
do { \
if ( locking ) \
l3t_lock(page); \
+ else \
+ block_lock_speculation(); \
} while ( false )
#define L3T_UNLOCK(page) \
@@ -5342,8 +5341,7 @@ int map_pages_to_xen(
if ( l3e_get_flags(ol3e) & _PAGE_GLOBAL )
flush_flags |= FLUSH_TLB_GLOBAL;
- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);
if ( (l3e_get_flags(*pl3e) & _PAGE_PRESENT) &&
(l3e_get_flags(*pl3e) & _PAGE_PSE) )
{
@@ -5447,8 +5445,7 @@ int map_pages_to_xen(
if ( l2e_get_flags(*pl2e) & _PAGE_GLOBAL )
flush_flags |= FLUSH_TLB_GLOBAL;
- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);
if ( (l2e_get_flags(*pl2e) & _PAGE_PRESENT) &&
(l2e_get_flags(*pl2e) & _PAGE_PSE) )
{
@@ -5489,8 +5486,7 @@ int map_pages_to_xen(
unsigned long base_mfn;
const l1_pgentry_t *l1t;
- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);
ol2e = *pl2e;
/*
@@ -5544,8 +5540,7 @@ int map_pages_to_xen(
unsigned long base_mfn;
const l2_pgentry_t *l2t;
- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);
ol3e = *pl3e;
/*
@@ -5689,8 +5684,7 @@ int modify_xen_mappings(unsigned long s, unsigned long e,
unsigned int nf)
l3e_get_flags(*pl3e)));
UNMAP_DOMAIN_PAGE(l2t);
- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);
if ( (l3e_get_flags(*pl3e) & _PAGE_PRESENT) &&
(l3e_get_flags(*pl3e) & _PAGE_PSE) )
{
@@ -5749,8 +5743,7 @@ int modify_xen_mappings(unsigned long s, unsigned long e,
unsigned int nf)
l2e_get_flags(*pl2e) & ~_PAGE_PSE));
UNMAP_DOMAIN_PAGE(l1t);
- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);
if ( (l2e_get_flags(*pl2e) & _PAGE_PRESENT) &&
(l2e_get_flags(*pl2e) & _PAGE_PSE) )
{
@@ -5794,8 +5787,7 @@ int modify_xen_mappings(unsigned long s, unsigned long e,
unsigned int nf)
*/
if ( (nf & _PAGE_PRESENT) || ((v != e) && (l1_table_offset(v) !=
0)) )
continue;
- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);
/*
* L2E may be already cleared, or set to a superpage, by
@@ -5842,8 +5834,7 @@ int modify_xen_mappings(unsigned long s, unsigned long e,
unsigned int nf)
if ( (nf & _PAGE_PRESENT) ||
((v != e) && (l2_table_offset(v) + l1_table_offset(v) != 0)) )
continue;
- if ( locking )
- spin_lock(&map_pgdir_lock);
+ spin_lock_if(locking, &map_pgdir_lock);
/*
* L3E may be already cleared, or set to a superpage, by
diff --git a/xen/arch/x86/mm/mm-locks.h b/xen/arch/x86/mm/mm-locks.h
index 273fff86ba..2eae73ac68 100644
--- a/xen/arch/x86/mm/mm-locks.h
+++ b/xen/arch/x86/mm/mm-locks.h
@@ -335,6 +335,15 @@ static inline void p2m_unlock(struct p2m_domain *p)
#define p2m_locked_by_me(p) mm_write_locked_by_me(&(p)->lock)
#define gfn_locked_by_me(p,g) p2m_locked_by_me(p)
+static always_inline void gfn_lock_if(bool condition, struct p2m_domain *p2m,
+ gfn_t gfn, unsigned int order)
+{
+ if ( condition )
+ gfn_lock(p2m, gfn, order);
+ else
+ block_lock_speculation();
+}
+
/* PoD lock (per-p2m-table)
*
* Protects private PoD data structs: entry and cache
diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 4dd41193f5..ca24cd4a67 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -281,9 +281,8 @@ mfn_t p2m_get_gfn_type_access(struct p2m_domain *p2m, gfn_t
gfn,
if ( q & P2M_UNSHARE )
q |= P2M_ALLOC;
- if ( locked )
- /* Grab the lock here, don't release until put_gfn */
- gfn_lock(p2m, gfn, 0);
+ /* Grab the lock here, don't release until put_gfn */
+ gfn_lock_if(locked, p2m, gfn, 0);
mfn = p2m->get_entry(p2m, gfn, t, a, q, page_order, NULL);
diff --git a/xen/include/xen/spinlock.h b/xen/include/xen/spinlock.h
index 8430a888a8..e351fc9995 100644
--- a/xen/include/xen/spinlock.h
+++ b/xen/include/xen/spinlock.h
@@ -229,6 +229,14 @@ static always_inline void spin_lock_irq(spinlock_t *l)
block_lock_speculation(); \
})
+/* Conditionally take a spinlock in a speculation safe way. */
+static always_inline void spin_lock_if(bool condition, spinlock_t *l)
+{
+ if ( condition )
+ _spin_lock(l);
+ block_lock_speculation();
+}
+
#define spin_unlock(l) _spin_unlock(l)
#define spin_unlock_irq(l) _spin_unlock_irq(l)
#define spin_unlock_irqrestore(l, f) _spin_unlock_irqrestore(l, f)
--
generated by git-patchbot for /home/xen/git/xen.git#staging
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